Cobalt pyrite (CoS2) is considered to be a promising catalyst for the hydrogen evolution reaction (HER) due to its intrinsic metallicity and high catalytic activity. However, the catalytically inert S-sites and sluggish reaction kinetics severely impede its commercial application. Herein, combining systematic theoretical and experimental approaches, a highly active and stable Cu doped CoS2 catalyst for the HER is demonstrated. Cu dopants are proven to not only reduce the hydrogen adsorption free energy (ΔGH*) of the Co sites from 0.41 eV to −0.13 eV, but also arouse the inert S sites with the low ΔGH* of −0.11 eV. A large cathode current density (10 mA cm−2 at 52 mV), low Tafel slope (42 mV dec−1), large exchange current density (0.68 mA cm−2), and good stability were observed in the Co0.93Cu0.07S2 catalyst, which are better than those found for the previously reported CoS2-based catalysts. The success of improving the electrochemical performance via the introduction of Cu dopants offers new opportunities in the development of high performance CoS2-based electrodes for other energy-related applications.

It should be a promising paradigm for graphene application in semiconductor industry by incorporating graphene into silicon to improve the behavior of silicon-based devices or develop high-performance devices with a new physical mechanism. Here we report on a large positive magnetoresistance (MR) over 80% at a magnetic field of 2.2 T and a temperature of 80 K in graphene/Si Schottky junctions by stacking chemical vapor deposition derived monolayer graphene on silicon. The produced MR is anisotropic and dependent on the angle between the direction of the magnetic field and the configuration plane, and can be modulated by the electrical bias across the configuration due to the built-in electric field. The MR effect should be ascribed to the charge carriers scattering and the released silicon magnetic moments in the graphene/Si interface that is suggested by first principles calculations. The study here should be helpful to understand the interface between the graphene and silicon, develop high-performance silicon based devices, complement the extraordinary properties of graphene and open one possible way to exploit their application for magneto-electronics.Download high-res image (272KB)Download full-size image

Palladium–cobalt alloy nanoparticles were synthesized and dispersed on carbon black support, aiming to have a less expensive catalyst. Catalytic behaviors of PdCo/C catalyst for the oxidation of hydroquinone (HQ) with H2O2 in aqueous solution were evaluated using high-performance liquid chromatography (HPLC). The results revealed that PdCo/C catalyst had better catalytic activity than an equal amount of commercial Pd/C and Co/C catalysts because of the d-band hybridization between Pd and Co. The effects of pH value, solvent, and various interferents including inorganic and organic compounds on the efficiency of HQ oxidation were further investigated. Furthermore, on the basis of mixed potential theory, comprehensive electrochemical measurements such as the open-circuit potential-time (OCP-t) technique and Tafel plot were efficient to assess the catalytic activity of the catalyst, and the results obtained were consistent with those of HPLC measurements. The efficient HQ oxidation was closely associated with the catalytic activity of PdCo nanoparticles because they accelerated the electron-transfer process and facilitated the generation of OH radicals.Keywords: free radicals; interferences; mixed potential measurement; oxidation of hydroquinone; PdCo alloy nanoparticles

Two-dimensional ferromagnetic metal-free materials possessing only an s/p electronic configuration with weak spin–orbit coupling and a large spin relaxation time play a crucial role in constructing future spintronic devices. Here, we demonstrate a novel two-dimensional material, fluorinated graphitic carbon nitride (g-C3N4) nanosheets, with intrinsic ferromagnetism; its Curie temperature can reach as high as 700 K. More surprising is that such unusual ferromagnetism can be further tuned by changing the concentration of fluorine. The tuneable electronic spin polarization, as well as the ferromagnetism observed in the fluorinated g-C3N4 nanosheets is quite promising for future device applications in spintronics.

Two-dimensional ferromagnetic ultrathin nanosheets hold great promise for next generation electronics and spintronics. Here, intrinsic ferromagnetism was achieved through a new effective strategy by fluorine adsorption on MoS2 nanosheets, where the fluorinated MoS2 nanosheets exhibit stable ferromagnetic hysteresis at room temperature with saturation magnetization of 0.06 emu g−1 and magnetoresistance of 4.1%. The observed ferromagnetism can be tuned by changing the concentration of the adatom. On the basis of first-principle calculations, it is shown that not only fluorine absorbed MoS2 monolayer favours spontaneous spin polarization and local moment formation, but also that the spin moments can exhibit long range magnetic ordering. This work paves a new pathway to engineer the magnetic properties of the two-dimensional nano-materials.

We report non-volatile electric-field control of magnetism modulation in Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) heterostructure by fabricating an epitaxial Fe layer on a PMN-PT substrate using a molecular beam epitaxy technique. The remnant magnetization with a different electric field shows a non-symmetric loop-like shape, which demonstrates a change of interfacial chemistry and a large magnetoelectric coupling in Fe/PMN-PT at room temperature to realize low loss multistate memory under an electric field. Fitting with the angular-dependence of the in-plane magnetization reveals that the magnetoelectric effect is dominated by the direct electric-field effect rather than the strain effect at the interface. The magnetoelectric effect and the induced surface anisotropy are found to be dependent on the Fe film thickness and are linear with respect to the applied electric field.

High Curie temperature ferromagnetism has been realized in atomically thin MoS2 and WS2 nanosheets. The ultrathin nanosheet samples were prepared via a novel, simple and efficient chemical vapor deposition method; different kinds of transition metal disulfides (MoS2 and WS2) could be obtained by sulphuring the corresponding cation sources (MoO3 and WCl6). Through related morphological and structural characterization, we confirm that large-area, uniform, few-layer MoS2 and WS2 nanosheets were successfully synthesized by this method. Both nanosheet samples exhibit distinct ferromagnetic behavior. By careful measurement and fitting of the magnetization of MoS2 and WS2 samples at different temperatures, we deconstruct the magnetization into its diamagnetic, paramagnetic and ferromagnetic contributions. The ferromagnetic contributions persist until 865 K for MoS2 and 820 K for WS2. We attribute the observed ferromagnetic properties to the defects and dislocations produced during the growth process, as well as the presence of edge spins at the edge of the nanosheets.

We report the new functionality of room temperature ferromagnetism in CuO–ZnO heterostructures. Magnetic measurement results indicate the CuO–ZnO heterostructures show enhanced ferromagnetism contrary to the pure CuO (ZnO) and the observed ferromagnetism is proportional to the interface counts for the film-heterostructures, providing proof of interface related ferromagnetism. Our study suggests that magnetically functional interfaces could be an entirely new and novel design of magnetic materials for emergent devices.

The Cu2O/Cu nanoparticle composites have been fabricated by heating a mixture of copper nitrate and different amounts of glycine. Magnetic measurement results indicate that the Cu2O/Cu composites show clear ferromagnetism, while the pure Cu2O and Cu show diamagnetism only. Through analyzing the photoluminescence X-ray photoelectron spectroscopy results, we proposed that the observed tunable ferromagnetism for the samples is attributed to Cu vacancies, where the interface of Cu2O/Cu composites plays an important role in modulating the concentration of Cu vacancies.

Layered transition metal dichalcogenides (TMDs) are now playing important roles in both fundamental studies and technological applications due to their special structures and rich physical properties. Here, hierarchical ultrathin TMD nanosheets based on molybdenum sulphoselenides [Mo(SxSe1−x)2] with tunable ferromagnetism were synthesized by a one step hydrothermal method. In addition, the hierarchical ultrathin Mo(SxSe1−x)2 nanosheets exhibit excellent composition-dependent electrocatalytic properties for the hydrogen evolution reaction (HER). It is considered that the intrinsic ferromagnetism and the efficient HER activity are related to the defect sites in the samples. This finding opens up a way to alter the ferromagnetism and electroactivity of layered chalcogenides by fine tuning of the composition.

Epitaxial CaTiO3 films, with smooth and dense surface, were fabricated by the promising hydrothermal synthesis on the Nb:SrTiO3(001) substrate. The resulting coated substrates was used to prepare Pt/CaTiO3/Nb:SrTiO3 heterostructure devices. The devices present a bipolar resistive switching behavior. Both high and low resistance states have not obvious degradation within ∼3 h and 1000 cycles measurements, which demonstrates the devices possess excellent retention and endurance characteristics. The resistive switching behavior of the devices can be explained by the trap-controlled space charge limited current conduction mechanism. Moreover, the modulation of the Pt/CaTiO3 Schottky-like barrier under an applied electric field is also responsible for the switching behavior, in the carrier injection-trapped/detrapped process.

•BFO films are epitaxially grown on NSTO (001) substrate by hydrothermal method.•The Pt/BFO/NSTO devices exhibit multilevel bipolar resistive switching behavior.•The Pt/BFO/NSTO devices possess excellent retention and endurance characteristics.A crystalline BiFeO3 (BFO) heteroepitaxial film was produced by mild hydrothermal epitaxy on a Nb–SrTiO3(100) (NSTO) substrate. The resulting coated substrate was used to fabricate a Pt/BFO/NSTO heterostructure device. The device exhibits reversible bipolar resistive switching behavior. The resistance states can be reversibly switched among multiple levels, by changing the magnitude of the reset pulse voltage. This illustrates the devices potential in multilevel nonvolatile memory devices. The resistive switching behavior of the device is attributed to trap-controlled space-charge-limited current conduction, which is controlled by oxygen vacancies in the film. The modulation of the Pt/BFO Schottky-like junction depletion under an applied electric field is thought to be responsible for the resistance switching behavior of the device, in the carrier injection-trapped/detrapped process.An epitaxial BiFeO3 (BFO) film, with crack-free and compact surface, is hydrothermally grown on a single-crystal Nb-doped SrTiO3 (NSTO) (001) substrate. The stable tri-state bipolar switching behavior of a ReRAM device containing the Pt/BFO/NSTO structure is achieved by changing the reset voltage (−2 V and −3 V) at room temperature.

In order to systematically investigate the influence of the interface on the magnetic properties, polycrystalline NiZn ferrite thin films were irradiated with 60 keV proton in the dose range from 5 × 1012 to 5 × 1016 ions/cm2. A non-destructive approach by proton irradiation was found to finely adjust the magnetic properties of polycrystalline NiZn ferrite thin films such as coercivity, perpendicular magnetic anisotropy as well as the effective g value. The coercivity is about 725 Oe for high proton dose ferrite, which is twice larger than the unirradiated one. The ferromagnetic resonance measurements indicated that perpendicular magnetic anisotropy and the effective g value increase with the irradiation dose. Our finding indicates that all modifications of these magnetic properties were associated with the change of interface due to the diffusion and the stress induced by proton irradiation. The change of the effective g value is a result of lattice expansion and the decrease of the magnetic dipole interaction between the columnar grains. This work provides a feasible way to tailor the magnetic properties of thin films by ion irradiation and promotes investigations for the stability of magnetic thin film devices in space or unclear radiation environments.

We report a pronounced angular dependence of the magnetoresistance (MR) effect in a silicon based p–n junction device at room temperature by manipulating the space charge region of the p–n junction under a magnetic field. For the p–n junction device with various space charge region configurations, we find that all the angular dependence of the MR effect is proportional to sin2(θ), where the θ is the angle between the magnetic field and the driving current. With increasing the magnetic field and driving current, the anisotropic MR effect is obviously improved. At room temperature, under a magnetic field 2 T and driving current 20 mA, the MR ratio is about 50%, almost one order of amplitude larger than that in the magnetic material permalloy. Our results reveal an interpretation of the MR effect in the non-magnetic p–n junction in terms of the Lorentz force and give a new way for the development of future magnetic sensors with non-magnetic p–n junctions.

Ultrathin metal-free g-C3N4 nanosheets with intrinsic room temperature ferromagnetism were synthesized by heating urea in an airtight container at different temperatures. Results indicate that the samples' saturation magnetization increases with the carbon defect concentration, revealing its carbon defect related ferromagnetism. Moreover, we further confirmed the defect induced ferromagnetic nature by ab initio calculations. It is believed that this finding highlights a new promising material toward realistic metal-free spintronic application.

•Pt flowerlike nanocrystals on PDA/RGO are prepared via chemical reduction.•Heating and PDA modification are necessary to synthesize Pt flowerlike crystals.•Pt(F)-PDA/RGO exhibits excellent catalytic activity for methanol electro-oxidation.•Pt(F)-PDA/RGO is easily activated and keeps good catalytic stability.A simple and effective approach was demonstrated to synthesize flowerlike Pt nanocrystals on polydopamine (PDA) functionalized reduced oxide graphene (RGO). Inspired by mussels, the PDA/RGO composites were obtained via the reduction of GO nanosheets by dopamine, followed by simultaneous capping by PDA. Then, the synthesis of Pt flowerlike nanocrystals assembled with small elongated nanoparticles on PDA/RGO (Pt(F)-PDA/RGO) was carried out by mixing H2PtCl6 with PDA/RGO in the presence of ascorbic acid under boiling. PDA as a surface-adherent and multifunctional biopolymer played a dual role: dispersing stable RGO into aqueous solution and providing functional groups to bind metal ions and metal nanoparticles. The as-prepared Pt(F)-PDA/RGO catalyst showed considerably improved catalytic activity and stability toward methanol electrooxidation, compared with Pt nanoclusters on PDA/RGO (Pt(C)-PDA/RGO) and Pt nanoparticles on pristine graphene sheets (Pt/RGO). The kinetic characterization of Pt(F)-PDA/RGO was further discussed by cyclic voltammetry. This simple and green approach could be applicable to other metallic nanocrystals as a novel platform in catalysis, fuel cells and biosensors.Figure optionsDownload full-size imageDownload as PowerPoint slide

Two-dimensional nanomaterials usually have abnormal physical properties due to surface effects and large edge states. In this communication, it is demonstrated that porous hexagonal disulfide nanosheets exhibit clear room temperature ferromagnetism, where the observed ferromagnetism can be tuned by changing the porosity of the nanosheets. The disordered grain boundary, or defects in the nanosheets, is considered to be responsible for the long-range magnetic order. This finding suggests a route to facilitate the design of nanoelectronic devices.

The possibility of inducing long-range ferromagnetic order with non-transition metal ions has become a very exciting challenge in recent years. In order to elucidate the room temperature ferromagnetism of SnO2 powders, the magnetic properties of SnO2 powders that have been mechanically milled and subsequently annealed have been investigated. The results indicate that saturation magnetization of the samples increases with milling time, where a high saturation magnetization of 0.0012 emu g−1 can be obtained for the sample milled for 20 h, and saturation magnetization for the sample decreases gradually after annealing in air. Electron spin resonance results show large numbers of singly-charged oxygen vacancies on the surfaces of the SnO2 powders. Combined with X-ray photoelectron spectroscopy and room temperature photoluminescence results, this suggests that the observed ferromagnetism is related to the singly-charged oxygen vacancies.

Antiferromagnetic nanoparticles as ultimate low-dimensional materials potentially give novel magnetic properties that differ from their bulk form due to strong quantum and surface effects. Herein, we propose that the observed anomalous ferromagnetic behavior of NiO nanoparticles is due to the formation of a ferromagnetic particle shell that is oxygen-vacancy related. A novel self-consistent estimation of the saturation magnetization further confirmed our proposal. The samples, synthesized by a thermal decomposition method, exhibit diversely anomalous ferromagnetic behavior, such as hysteresis curves, large coercivities, exchange bias and spin-glass behavior. A large saturation magnetization of 0.536 emu g−1 exists in the 6 nm NiO sample and it is found to decrease with increasing crystal size. Neither impurity element nor change of valence state has been found in the samples, through X-ray photoelectron, X-ray diffraction or selected-area electron diffraction measurements. Remarkably, a large amount of oxygen vacancies exists, which was verified by X-ray photoelectron spectrum fitting results and Raman spectroscopy. A post-hydrogen-annealing process strongly elevates ferromagnetic ordering, as a result of surface defect enhancement. Moreover, our estimation of the saturation magnetization based on first principle calculation results is in agreement with the experimental conclusion, which reveals the significance of surface states in mediating anomalous magnetic properties in low-dimensional antiferromagnetic materials.

The unexpected room temperature ferromagnetism in pure sodium chloride (NaCl) particles with different crystal size synthesized by breaking at different times is attributed to surface defects, which provides a novel opportunity to further understand the origin of ferromagnetism in the traditional “nonmagnetic” inorganic non-metallic materials. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy suggest that breaking progress does not change the samples' body, but drastically reduces the size of the samples, what's more, it is found to enhance the strength of the ferromagnetic component with decreasing the samples' size through magnetism measure; the first-principle calculation results confirm the experimental conclusion. Ferromagnetism originates from surface effect, probably the long range ferromagnetic interactions between the surface Cl vacancies.

Two-dimensional nanosheet crystals have potential applications in nano-electronic devices. Prompted by the recently observed ferromagnetism in pristine VX2 (X = S and Se) monolayers by first-principle calculations, we provide the experimental evidence for room temperature ferromagnetism in ultrathin VS2 nanosheets by observing their clear hysteresis and ferromagnetic resonance. The first-principle calculation results indicate that unusual hybridization of the V 3d and S 3p orbitals occurs in the monolayer VS2, and the relative transfer of electrons between the V and S atoms plays an important role in the transition of the spin moments. According to the previous work, the stable ferromagnetism in ultrathin VS2 nanosheets is considered as a competitive effect between through-bond and through-space interactions, where the through-bond interactions dominate. This finding opens a new path to explore the spintronics in pristine two-dimensional nanostructures.

Hierarchical Co3O4 mesoporous nanostructures have been synthesized by a hydrothermal method combined with subsequent calcination. These hierarchical nanostructures were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. According to varying the reaction time, three typical kinds of Co3O4 hierarchical nanostructures, i.e., free-standing nanowalls, nanowires-nanowalls, and, nanosheets-nanowires-nanowalls were obtained. The formation of mesoporous Co3O4 nanostructures may be due to the thermal decomposition of the corresponding precursor. Magnetic measurement indicates that the vacuum-annealed Co3O4 samples show room temperature ferromagnetism, while the as-prepared samples are paramagnetic.

In this paper, we present a facile approach to fabricate open-cell Ni foams by annealing the colloid of Ni(NO3)2 and 2-methoxyethanol (C3H8O2) in air. X-Ray diffraction and selected area electron diffraction results show that the products are single crystal Ni in the face-centered cubic (fcc) phase. This result was confirmed by the peak corresponding to zero valence of Ni in X-ray photoelectron spectroscopy. Scanning electron microscopy results reveal the 3-dimensional geometry open-cell foam structure of the products. The average aperture size of the Ni foam is about 300 nm and the wall stent is about 250 nm with an Ni2+ concentration of 0.35 M in the colloid. The porosity of the products decreases gradually with increasing Ni2+ concentration in C3H8O2. Owing to its uniform 3-D structure with high porosity and high specific surface area, the open cell Ni foams may have some potential applications, such as magnetic flux conductors or an ideal electrode material for high energy MH/Ni and Cd/Ni batteries, etc.

Nanoparticles of superconducting YBa2Cu3O7−δ were synthesized via a citrate pyrolysis technique. Room temperature ferromagnetism was revealed in the samples by a vibrating sample magnetometer. Electron spin resonance spectra at selected temperatures indicated that there is a transition from the normal to the superconducting state at temperatures below 100 K. The M–T curves with various applied magnetic fields showed that the superconducting transition temperatures are 92 K and 55 K for the air-annealed and the post-annealed samples, respectively. Compared to the air-annealed sample, the saturation magnetization of the sample by reheating the air-annealed one in argon atmosphere is enhanced but its superconductivity is weakened, which implies that the ferromagnetism maybe originates from the surface oxygen defects. By superconducting quantum interference device measurements, we further confirmed the ferromagnetic behavior at high temperatures and interesting upturns in field cooling magnetization curves within the superconducting region are found. We attributed the upturn phenomena to the coexistence of ferromagnetism and superconductivity at low temperatures. Room temperature ferromagnetism of superconducting YBa2Cu3O7−δ nanoparticles has been observed in some previous related studies, but the issue of the coexistence of ferromagnetism and superconductivity within the superconducting region is still unclear. In the present work, it will be addressed in detail. The cooperation phenomena found in the spin-singlet superconductors will help us to understand the nature of superconductivity and ferromagnetism in more depth.

[NiFe/FeMn]n exchange-coupled multilayer films have been fabricated on the silicon substrate by magnetron sputtering deposition. The static and dynamic magnetic properties of multilayer films have been investigated with varying numbers of layers. The results show that the linewidth and permeability of imaginary resonance peak are increased with increasing numbers of layers. For the NiFe/FeMn/NiFe sample, the resonance frequency shows a different shift with applying external magnetic field along the direction of easy and hard magnetization axis of the sample, respectively, indicating a different magnetic reversal process in two ferromagnetic layers. It proved that the increase of linewidth was originated from the different interface exchange coupling.

A correlation between oxygen vacancies and the magnetization for pure zinc peroxide nanoparticles (∼7 nm) synthesized by the hydrothermal method is demonstrated. Occurrence of room temperature ferromagnetism for zinc peroxide nanoparticles is established by the observed hysteresis loops and the ferromagnetic resonance signal. X-ray photoelectron spectroscopy and photoluminescence results reveal the oxygen insufficiency in the samples. The variation of oxygen vacancies concentration is consistent with the changes of the saturation magnetization for the samples. Combining with the results of electron spin resonance, it is suggested that the singly occupied oxygen vacancies forming the F+ centers play the key role in the exchange mechanism.

Co100−xSnx alloy nanowires were fabricated by electrodeposition of Co2+ and Sn2+ into anodic aluminum oxide (AAO) templates. X-ray diffraction results indicate that the crystal structures of the nanowires changed from polycrystal to amorphism, and then to polycrystal again with the increase of Sn content in the nanowires. Transmission electron microscopy result shows that the nanowires are about 50 nm in diameter and the aspect ratio is approximately 75. The magnetic response of the arrays was measured using vibrating sample magnetometry at room temperature. The results show that the coercivity and squareness with the magnetic field along the nanowire arrays decrease with the increase of the Sn content. Nanowires exhibit obviously uniaxial magnetic anisotropy, and the easy magnetizing axis is parallel to the nanowires owing to the large shape anisotropy.

Flowerlike CuO nanostructures were prepared by the coprecipitation method with postannealing in air at different temperatures. The results of X-ray diffraction and Raman and X-ray photoelectron spectroscopies show that the samples annealed at 400, 600, and 800 °C have a typical monoclinic structure and are absent of impurity phases. Magnetic measurements indicate that all of the CuO nanostructures show room-temperature ferromagnetism, whereas CuO bulk presents paramagnetism. The saturation magnetization of the samples was found to increase with increasing annealing temperature. The fitting results of the O 1s XPS spectra for the three samples indicate that oxygen vacancies exist in the samples and that the variation of the oxygen vacancy concentration is in complete agreement with the variation of the saturation magnetization. When the samples were annealed in oxygen atmosphere, the ferromagnetism of the samples decreased enormously. These results confirm that the observed room-temperature ferromagnetism in flowerlike CuO nanostructures might originate from oxygen vacancies.

Single-crystalline CoO nanospheres with the size distribution between 40 and 250 nm were prepared by a solvothermal method. Magnetic measurements indicate that the vacuum-annealed samples show room temperature ferromagnetism except for the CoO nanospheres of 250 nm, which still exhibit paramagnetism after being postannealed in vacuum atmosphere (10−3 Pa) at 250 °C as others. The saturation magnetization of all postannealed samples monotonically increases with the decrease of nanosphere diameter. No other impurity phases are observed for the postannealed samples, indicating that the revealed ferromagnetism is an intrinsic property. The fitted XPS results of O 1s spectra indicate that the variations of oxygen vacancies concentration are consistent with the variations of saturation magnetization for the vacuum-annealed samples, suggesting that the formed oxygen vacancies at the surface of the CoO nanospheres during the vacuum-annealing process account for the observed ferromagnetism.

The intrinsic nature of ferromagnetism in CaO nanopowders has been established with the experimental observation of magnetic hysteresis loop at room temperature. On the basis of the results of X-ray diffraction, magnetic properties, positron annihilation lifetime spectra, and first-principles calculations, it is found that there are correlations among the lattice constant, the defect concentration, and the magnetization of CaO nanopowders, which suggests that Ca defects are the main reason for the magnetic order and the defect concentration is related with the ferromagnetism. Such a ferromagnet without the presence of any transition metal could be a very good option for a class of spintronics.

The room-temperature ferromagnetism of Zn1−xAlxO nanoparticles synthesized by a sol−gel method is reported in this paper. X-ray diffraction and selected area electron diffraction results show that the Al atoms have successfully substituted for some of the Zn atoms in the ZnO lattice without forming other new phases. The results also show that the samples possess a typical wurtzite structure. Declaration of ferromagnetism at room temperature has been established with the observed hysteresis and the coercive field in hysteresis loops. Magnetic measurements indicate that the saturation magnetization of the samples is sensitive to the content of Al dopants and that, for Zn0.97Al0.03O, the saturation magnetization reaches the maximum of 0.012 emu/g. Combining with the results of Raman, photoluminescence, and X-ray photoelectron spectroscopies, it is suggested that the observed ferromagnetic ordering of the Zn1−xAlxO nanoparticles is related to the doping-induced oxygen vacancies.

Preferred oriented ZnFe2O4 nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe2 nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe2O4 nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe2O4 nanowire arrays give out 370–520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively.

Room temperature ferromagnetism (RTF) is observed in pure copper oxide (CuO) nanoparticles which were prepared by precipitation method with the post-annealing in air without any ferromagnetic dopant. X-ray photoelectron spectroscopy (XPS) result indicates that the mixture valence states of Cu1+ and Cu2+ ions exist at the surface of the particles. Vacuum annealing enhances the ferromagnetism (FM) of CuO nanoparticles, while oxygen atmosphere annealing reduces it. The origin of FM is suggested to the oxygen vacancies at the surface/or interface of the particles. Such a ferromagnet without the presence of any transition metal could be a very good option for a class of spintronics.

CoFe2O4 nanowire arrays were fabricated by electrodeposition of Fe2+ and Co2+ into anodic aluminum oxide (AAO) templates and further oxidization. The phase structure of the nanowires is cubic spinel-type, and the XRD result exhibits perfect preferred crystallite orientation along the nanowire axes. Compared with CoFe2O4 nanowire arrays synthesized by other methods, the magnetic hysteresis loops demonstrate that the arrays of nanowires exhibit uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axes owing to the large shape anisotropy. This approach provides a facile technology to fabricate oxide nanowires with uniaxial magnetic anisotropy.

Arrays of Cu-doped ZnO nanowires were successfully fabricated by electrodeposition of Zn2+ and Cu2+ into anodic aluminum oxide template and post-oxidation annealing in air atmosphere. The transmission electron microscopy result shows that the nanowires are uniform, about 100 nm in diameter and with the aspect ratio of up to 40. Selected area electron diffraction and X-ray diffraction results indicate that the nanowires are in hexagonal wurtzite structure. Magnetization measurements show that the Zn1−xCuxO (x = 0.07 and 0.11) nanowires exhibit room-temperature ferromagnetism and the enhancement of the ferromagnetism is revealed for the Zn0.93Cu0.07O nanowires annealed in vacuum.

The coaxial nanocables of Fe/Fe−dimethylsulfoxide (DMSO) were electrodepositied at 40 °C in the solution of DMSO with 17 g/L FeCl3. It is the first report about the preparation of nanocables by electrodeposition in a simple one-step process. The Fe−DMSO sheaths are predicted as coordination compounds of [Fe(DMSO)4Cl2] and [Fe(DMSO)3Cl3] that are amorphous in structure and paramagnetic at room temperature. The Fe cores are bcc structure with a preferred orientation of (110). The morphology of resulting nanostructures can be precisely controlled by varying the concentration of FeCl3 in DMSO solution and the elelctrodeposited temperature. The walls of Fe−DMSO sheaths are very thin; therefore, the outer diameters of nanocables are nearly the same as the central Fe cores about 40 nm, with an aspect ratio of 100. The arrays exhibit an obvious anisotropy with the easy magnetizing axis along the length of nanocables, which are useful magnetic storage materials.

This paper reports the synthesis and characterization of multiferroic BiFeO3 nanotubes. Perovskite BiFeO3 nanotubes with outer diameters 150–190 nm were synthesized by a facile sol–gel template method. The photoabsorption of BiFeO3 nanotubes was characterized by UV–visible diffuse reflectance spectrometry. The BiFeO3 nanotubes show weak ferromagnetism at room temperature, unlike the antiferromagnetic order in bulk BiFeO3, reflecting the grain size-confinement effect on the magnetic ordering of BiFeO3.

Bi1−xSrxMn0.2Fe0.8O3 ceramics have been prepared by sol–gel process, and their physical properties have been studied. These samples exhibit enhanced ferromagnetization without disturbing their ferroelectric properties. The X-ray photoelectron spectroscopy (XPS) results reveal the origin of spontaneous magnetization in these samples. Adding Sr2+ ions to BiMn0.2Fe0.8O3 system requires charge compensation, which can be achieved by formation of Mn4+. The statistical distribution of Mn3+ and Mn4+ ions in the octahedral leads to net magnetization and ferromagnetism.

Self-organized and ordered CoFe2O4 nanotube arrays were prepared in porous anodic aluminum oxide template using an improved sol–gel approach. The attraction between the negatively charged sol particles and the positively charged pore wall of AAO is the causation of tube formation process. The morphology was studied by transmission electron and high-resolution field emission scanning electron microscope. A polycrystalline phase of the nanotube was found by X-ray and select area electron diffraction. Magnetic measurements showed that the magnetic orientation was weak in the arrays of nanotube, and the reason has been discussed.

Arrays of Fe61Co27P12 nanowire with an aspect ratio about 70 were prepared in anodic aluminum oxide templates by electrodeposition. The influences of annealing temperature on structure and magnetic properties of Fe61Co27P12 nanowires were studied. When the specimens were annealed below 400 °C, there are no obvious changes in structure except relaxation. With the annealing temperature increasing from 400 to 600 °C, the Fe–Co phase is detected by X-ray diffraction and Mössbauer spectra. The crystalline fraction and hyperfine field can be derived from Mössbauer spectra. The room temperature magnetic hysteresis loops show that the coercivity and squareness of the nanowire arrays in parallel to the wire axis increase with the increasing of annealing temperature, which mainly attributes to the strengthening of anisotropy.

Fe antidot arrays have been fabricated by ion beam sputtering method onto the porous alumina templates. Conversion electron Mössbauer spectroscopy was used to describe the magnetic moment distribution of the Fe antidot arrays. A component of the magnetic moment was found in the perpendicular direction of the film plane. The experimental results of magnetic moment distribution can be well explained by a simple model.

Co100−xSnx alloy nanowires were fabricated by electrodeposition of Co2+ and Sn2+ into anodic aluminum oxide (AAO) templates. X-ray diffraction results indicate that the crystal structures of the nanowires changed from polycrystal to amorphism, and then to polycrystal again with the increase of Sn content in the nanowires. Transmission electron microscopy result shows that the nanowires are about 50 nm in diameter and the aspect ratio is approximately 75. The magnetic response of the arrays was measured using vibrating sample magnetometry at room temperature. The results show that the coercivity and squareness with the magnetic field along the nanowire arrays decrease with the increase of the Sn content. Nanowires exhibit obviously uniaxial magnetic anisotropy, and the easy magnetizing axis is parallel to the nanowires owing to the large shape anisotropy.

Ni0.45Zn0.55Fe2O4 (40 nm) single-layer and Fe50Mn50 (25 nm)/Ni0.45Zn0.55Fe2O4 (40 nm) bilayer films were prepared on Si(111) substrates by radio frequency magnetron sputtering at room temperature, and the influence of FeMn underlayer on the microstructure and magnetic property of Ni–Zn ferrite film has been investigated. It was found that the introduction of Fe50Mn50 underlayer resulted in a decrease from 7.1 to 3.1 kA/m in coercivity and increase from 0.22 to 0.60 in residual magnetization ratio of the ferrite film. The complex permeability μ = μ′ − iμ″ values of the films were measured at a frequency of up to 5 GHz. An obvious resonance peak at about 1.65 GHz of the bilayer film appeared in the permeability spectrum. The reason has been researched preliminarily and was ascribed to the change of the film's microstructure with FeMn underlayer.Highlights►NiZn ferrite and FeMn/NiZn ferrite films are prepared by sputtering. ►The coercivity of the film with FeMn decreases from 7.1 to 3.1 kA/m. ►The residual magnetization ratio of the film with FeMn increases from 0.22 to 0.60. ►The film with FeMn shows a high resonance peak with 1.65 GHz. ►It is ascribed to the change of the film's microstructure with FeMn.

Two-dimensional ferromagnetic metal-free materials possessing only an s/p electronic configuration with weak spin–orbit coupling and a large spin relaxation time play a crucial role in constructing future spintronic devices. Here, we demonstrate a novel two-dimensional material, fluorinated graphitic carbon nitride (g-C3N4) nanosheets, with intrinsic ferromagnetism; its Curie temperature can reach as high as 700 K. More surprising is that such unusual ferromagnetism can be further tuned by changing the concentration of fluorine. The tuneable electronic spin polarization, as well as the ferromagnetism observed in the fluorinated g-C3N4 nanosheets is quite promising for future device applications in spintronics.

The unexpected room temperature ferromagnetism in pure sodium chloride (NaCl) particles with different crystal size synthesized by breaking at different times is attributed to surface defects, which provides a novel opportunity to further understand the origin of ferromagnetism in the traditional “nonmagnetic” inorganic non-metallic materials. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy suggest that breaking progress does not change the samples' body, but drastically reduces the size of the samples, what's more, it is found to enhance the strength of the ferromagnetic component with decreasing the samples' size through magnetism measure; the first-principle calculation results confirm the experimental conclusion. Ferromagnetism originates from surface effect, probably the long range ferromagnetic interactions between the surface Cl vacancies.

Two-dimensional nanosheet crystals have potential applications in nano-electronic devices. Prompted by the recently observed ferromagnetism in pristine VX2 (X = S and Se) monolayers by first-principle calculations, we provide the experimental evidence for room temperature ferromagnetism in ultrathin VS2 nanosheets by observing their clear hysteresis and ferromagnetic resonance. The first-principle calculation results indicate that unusual hybridization of the V 3d and S 3p orbitals occurs in the monolayer VS2, and the relative transfer of electrons between the V and S atoms plays an important role in the transition of the spin moments. According to the previous work, the stable ferromagnetism in ultrathin VS2 nanosheets is considered as a competitive effect between through-bond and through-space interactions, where the through-bond interactions dominate. This finding opens a new path to explore the spintronics in pristine two-dimensional nanostructures.

We report the new functionality of room temperature ferromagnetism in CuO–ZnO heterostructures. Magnetic measurement results indicate the CuO–ZnO heterostructures show enhanced ferromagnetism contrary to the pure CuO (ZnO) and the observed ferromagnetism is proportional to the interface counts for the film-heterostructures, providing proof of interface related ferromagnetism. Our study suggests that magnetically functional interfaces could be an entirely new and novel design of magnetic materials for emergent devices.

Nanoparticles of superconducting YBa2Cu3O7−δ were synthesized via a citrate pyrolysis technique. Room temperature ferromagnetism was revealed in the samples by a vibrating sample magnetometer. Electron spin resonance spectra at selected temperatures indicated that there is a transition from the normal to the superconducting state at temperatures below 100 K. The M–T curves with various applied magnetic fields showed that the superconducting transition temperatures are 92 K and 55 K for the air-annealed and the post-annealed samples, respectively. Compared to the air-annealed sample, the saturation magnetization of the sample by reheating the air-annealed one in argon atmosphere is enhanced but its superconductivity is weakened, which implies that the ferromagnetism maybe originates from the surface oxygen defects. By superconducting quantum interference device measurements, we further confirmed the ferromagnetic behavior at high temperatures and interesting upturns in field cooling magnetization curves within the superconducting region are found. We attributed the upturn phenomena to the coexistence of ferromagnetism and superconductivity at low temperatures. Room temperature ferromagnetism of superconducting YBa2Cu3O7−δ nanoparticles has been observed in some previous related studies, but the issue of the coexistence of ferromagnetism and superconductivity within the superconducting region is still unclear. In the present work, it will be addressed in detail. The cooperation phenomena found in the spin-singlet superconductors will help us to understand the nature of superconductivity and ferromagnetism in more depth.

In this paper, we present a facile approach to fabricate open-cell Ni foams by annealing the colloid of Ni(NO3)2 and 2-methoxyethanol (C3H8O2) in air. X-Ray diffraction and selected area electron diffraction results show that the products are single crystal Ni in the face-centered cubic (fcc) phase. This result was confirmed by the peak corresponding to zero valence of Ni in X-ray photoelectron spectroscopy. Scanning electron microscopy results reveal the 3-dimensional geometry open-cell foam structure of the products. The average aperture size of the Ni foam is about 300 nm and the wall stent is about 250 nm with an Ni2+ concentration of 0.35 M in the colloid. The porosity of the products decreases gradually with increasing Ni2+ concentration in C3H8O2. Owing to its uniform 3-D structure with high porosity and high specific surface area, the open cell Ni foams may have some potential applications, such as magnetic flux conductors or an ideal electrode material for high energy MH/Ni and Cd/Ni batteries, etc.