Room Temperature Ferromagnetism Research Articles

Magnetic and electric behavior of spike- and petal-like nanoscaled Cu:ZnO superstructures diluted magnetic semiconductors

Room temperature ferromagnetism (RTFM) is the main condition for searching for materials to the application in spintronics. Beyond the candidates, the diluted magnetic semiconductors (DMS) are potential materials for such application. The introduction of a foreign transition metal ion in the semiconductor lattice may lead to the RTFM, where the intrinsic ferromagnetism developed by a nonmagnetic ion is preferable for spintronics application. In this work, single-phase Cu-substituted zinc oxide was synthesized by a fast polymeric precursor method, providing nanocrystallites from 4 to 11 nm. Copper hindered grain growth, even for high Cu concentrations. The crystallites assembled to superstructures with petal and spike-like morphologies, following an unconventional crystallization. The texturization observed during the crystallization led to the development of unexpected weak RTFM. The number of oxygen vacancies is too small to promote the RTFM since few atoms of copper find attached to the vacancies. Probably the RTFM arises from overlapped spin-split bound magnetic polarons (BMP) due to the interaction of the hybridized O 2p and localized unoccupied twofold t2 subband of Cu 3d states. Although the sintering of pure and Cu-doped ZnO particles was equivalent, the electrical properties diverged. The copper insertion enhanced the resistivity and the non-linearity coefficient reached values higher than the unity. This is maybe due to the presence of copper at the grain boundaries forming a Schottky barrier. Neither the non-ohmic electrical behavior nor the RTFM from nanostructured superstructures was ever reported before.

Morphology mediated photocatalysis and room temperature ferromagnetism in cerium oxide

Present work is focused on fine-tuning of magnetic and photocatalytic properties of three samples of cerium oxide nano/micro-sized particles synthesized via different chemical routes. X-ray diffraction measurement infers the growth of single phase cubic fluorite structure of pure CeO2 with a space group of Fm3‾m. The route of synthesis significantly altered the morphology and particle size as evident from high resolution transmission electron microscopy. Raman spectra and XPS confirmed the existence of oxygen vacancies defects in CeO2 matrix. In this article, investigations of magnetic properties and photocatalytic activity of rose Bengal dye in the presence of UV light have been carried out. For SG, CO, and HB samples, room temperature ferromagnetism was observed with small magnetizations of 2.21, 16.8, and 3.58 emu/g × 10−4 respectively. The photocatalytic efficiency of CO sample was 76.3% for degradation of rose Bengal dye on UV illumination for 140 min. Thus, morphology dependent enhanced ferromagnetic and superior photocatalytic behavior of CeO2 make it a multifunctional material for its use as a photocatalyst for organic dye decomposition and in spintronics devices.

Room-temperature ferromagnetic half-metallicity of two-dimensional oxyhalides CrOX2 (X = F, Cl) monolayers

Two-dimensional (2D) materials with room-temperature ferromagnetism and intrinsic wide half-metallic gap are superb candidates for pure spin generation, injection, and transport in nanospintronic applications. In this work, we disclose the magnetic and electronic properties of 2D transition metal oxyhalides CrOX2 monolayers and the effect of strain on them using first-principles calculations. Our results show that CrOX2 (X = F, Cl) exhibits intrinsic ferromagnetism and half metallicity with the half-metallic gap of more than 2 eV, as well as the phase transition temperature over 300 K when considering the Hubbard Ueff correction as 3.5 eV as obtained in most chromium oxide. Uniaxial strain can drive magnetic phase transition occur and the phase transition temperature enhance greatly. In addition, we also find that CrOF2 monolayer is mechanically, thermally and dynamically stable, but the CrOCl2 monolayer is only mechanically and thermally stable. These excellent properties of CrOX2 monolayers, in particular, CrOF2, make them hopeful for the fabrication of nanospintronic devices operating at room temperature.

Layer-Dependent Magnetoresistance and Spin-Transfer Torque in MnSe2 -Based Magnetic Tunnel Junctions

The recently synthesized two-dimensional van der Waals (vdW) ferromagnet 1T-${\mathrm{MnSe}}_{2}$ has attracted great attention due to its room-temperature ferromagnetism. By using ab initio quantum transport simulations with noncollinear spins, we demonstrate a monotonic increasing (decreasing) tendency of the angle-resolved tunneling magnetoresistance (spin-transfer torque) with the increasing graphene layer number n in the ${\mathrm{MnSe}}_{2}$/n-layer graphene/${\mathrm{MnSe}}_{2}$ (n = 1--4) vdW magnetic tunnel junctions (MTJs). A surprising tunneling magnetoresistance of around ${10}^{6}$% is obtained when $\ensuremath{\theta}={180}^{\ensuremath{\circ}}$ and n = 4 owing to the nearly perfect spin polarization; this is 3 orders of magnitude larger than that of the commonly used $\mathrm{MgO}$-based MTJ (1000% at 5 K). The maximal linear-response spin-transfer torque of the ${\mathrm{MnSe}}_{2}$/graphene/${\mathrm{MnSe}}_{2}$ MTJ (5260 \textmu{}eV/V) is 2 orders of magnitude larger than that of the $\mathrm{Fe}/\mathrm{MgO}/\mathrm{Fe}$ MTJ. The decay rate of the spin-transfer torkance at zero bias is revealed to be nonmonotonically n dependent. Meanwhile, the total spin-transfer torque in the device changes from linear dependence to nonlinear dependence as the bias voltage increases. Our calculation suggests that the 1T-${\mathrm{MnSe}}_{2}$-based vdW MTJs are promising in next-generation room-temperature nonvolatile memories.

Impact of Cr doping on the structure, optical and magnetic properties of nanocrystalline ZnO particles

The doping of Cr ions on the structure, optical and magnetic properties of ZnO have been investigated. Zn1−xCrxO (0 ≤ x ≤ 0.05) samples were prepared by the solution combustion method. Rietveld refined x-ray diffraction results reveal that all the samples are in a hexagonal structure. Transmission electron microscopy (TEM) revealed that the particle size was 48.2 ±2.1 nm, 29.4 ± 2.2 nm and 25.3 ± 2.1 nm for the Zn1−xCrxO with x = 0, 0.03 and 0.05, respectively. The band-gap decreases slightly from 3.308 ± 0.003 eV to 3.291 ± 0.003 eV with increase of Cr content from x = 0 to 0.05, respectively. The field-dependent magnetization M(μοH) measurements of ZnO and Cr-doped ZnO exhibit room temperature ferromagnetism (RTFM). Photoluminescence and electron paramagnetic resonance exhibits negatively charged zinc vacancies (VZn−) and singly ionized oxygen vacancies (Vo+) in ZnO and these defects are responsible for RTFM. And the VZn− accountable for RTFM in Cr-doped ZnO. EPR results confirmed that Cr3+ ions replaces the Zn2+ sites in the hexagonal ZnO. The observed long-range ferromagnetism ordering is explained based on the bound magnetic polaron (BMP) mechanism. This work elucidates the origin of RTFM in synthesized ZnO and Cr-doped ZnO.

Flat band induced room-temperature ferromagnetism in two-dimensional systems

Flat band induced room-temperature ferromagnetism in two-dimensional systems

Ferromagnetic single-atom spin catalyst for boosting water splitting.

Heterogeneous single-atom spin catalysts combined with magnetic fields provide a powerful means for accelerating chemical reactions with enhanced metal utilization and reaction efficiency. However, designing these catalysts remains challenging due to the need for a high density of atomically dispersed active sites with a short-range quantum spin exchange interaction and long-range ferromagnetic ordering. Here, we devised a scalable hydrothermal approach involving an operando acidic environment for synthesizing various single-atom spin catalysts with widely tunable substitutional magnetic atoms (M1) in a MoS2 host. Among all the M1/MoS2 species, Ni1/MoS2 adopts a distorted tetragonal structure that prompts both ferromagnetic coupling to nearby S atoms as well as adjacent Ni1 sites, resulting in global room-temperature ferromagnetism. Such coupling benefits spin-selective charge transfer in oxygen evolution reactions to produce triplet O2. Furthermore, a mild magnetic field of ~0.5 T enhances the oxygen evolution reaction magnetocurrent by ~2,880% over Ni1/MoS2, leading to excellent activity and stability in both seawater and pure water splitting cells. As supported by operando characterizations and theoretical calculations, a great magnetic-field-enhanced oxygen evolution reaction performance over Ni1/MoS2 is attributed to a field-induced spin alignment and spin density optimization over S active sites arising from field-regulated S(p)-Ni(d) hybridization, which in turn optimizes the adsorption energies for radical intermediates to reduce overall reaction barriers.

Room-temperature ferromagnetic half metal in (C, Mn) co-doped orthorhombic ZnO with large magneto-crystalline anisotropy energy

Room-temperature ferromagnetic (FM) half-metallic materials are essential for spintronics applications. Here, we find that (C, Mn) co-doped orthorhombic ZnO (termed (C, Mn) @Orth-ZnO) is a room-temperature FM half-metal with a magnetic moment of 3μ B per Mn atom. A detailed investigation of the electronic structure of the (C, Mn) @Orth-ZnO system demonstrates that the FM interaction originates mainly from the p–d exchange hybridization between the C2p and Mn3d states. Moreover, the induced extended spin-polarized states of nonmetallic C can mediate the long-range FM exchange interactions beyond the nearest-neighbor situation. The Curie temperature T C of the (C, Mn) @Orth-ZnO system is 371 K based on the mean-field approximation. The (C, Mn) @Orth-ZnO system also has a large magnetic anisotropy energy of 0.63 meV, which is mainly attributed to (dyz, dz 2) orbitals of the Mn atom. Finally, we discuss the influence of carrier concentration and external strain on the stability of the ferromagnetism of the (C, Mn) @Orth-ZnO system. We highlight the application prospects of (C, Mn) @Orth-ZnO in practical spintronic nano-devices.

Pure and Sm doped CeO2 Nanoparticles: An insight into the Room Temperature Ferromagnetism and Photocatalytic Dye Degradation

AbstractCeO2 nanoparticles (7–28 nm) and Sm‐doped (5, 10, 15, and 20 %) CeO2 nanoparticles are synthesized using a simple chemical precipitation technique. The defects are studied using Raman spectroscopy, and the presence of defects as oxygen vacancies is verified using the longitudinal optical mode. The optical band gap is determined using UV‐Vis spectroscopy. The reduction in the optical band gap with increasing particle size might be related to quantum confinement, which causes localized states to form due to oxygen vacancies when Ce4+ is reduced to Ce3+. An increase in band gap is observed with increasing Sm concentration, and the optical band gap is smaller than pure CeO2. The electronic structure is investigated using the X‐ray photoelectron spectroscopy (XPS) method, which studied the contributions of each ionic state, namely Ce3+ and Ce4+. Room temperature ferromagnetism (RTFM) is observed for doped as well as undoped samples. The saturation magnetization for 28 nm pure CeO2 NPs is obtained as Ms=5.6*10−4 emu/g, whereas for Sm‐doped samples, we found an increased value of 3.5*10−2 emu/g. The samples are scrutinized for UV‐irradiated photocatalytic dye degradation. The origin of RTFM behaviour and efficient photocatalytic activity are from oxygen vacancies at the lattice sites.

Oxygen Vacancy-Induced Ferromagnetism and Resistive-Magnetization Switching Characteristics in In2O3 Films

Ordered porous indium oxide thin films (In2O3) with higher ferromagnetism were prepared by the direct current magnetron sputtering method using porous anodic aluminum oxide thin films as the template. The experiment results show that the saturation magnetization reaches a maximum of about 42.03 emu/cm3 at a sputtering pressure of 3.2 Pa. The room-temperature ferromagnetism of In2O3 films mainly originates from the oxygen vacancies in the films. In addition, the spin can generally only be regulated by a magnetic field, which makes it challenging to realize miniaturization and integration of spin devices, while the regulation by an electric field can solve this contradiction. Based on this, the In2O3 composite thin-film resistive-magnetization switching device (Ag/In2O3/PAA/Al) was successfully prepared, showing bipolar resistive-magnetization switching characteristics and stable electrical and magnetic control characteristics. This research provides a way to develop a new multifunctional memory combining magnetic and resistive-magnetization storage and lays the foundation for the application of In2O3 in spintronic devices.

Emerging Enhancement and Regulation Strategies for Ferromagnetic 2D Transition Metal Dichalcogenides.

Two-dimensionaltransition metal dichalcogenides (2D TMDs) present promising applications in various fields such as electronics, optoelectronics, memory devices, batteries, superconductors, and hydrogen evolution reactions due to their regulable energy band structures and unique properties. For emerging spintronics applications, materials with excellent room-temperature ferromagnetism are required. Although most transition metal compounds do not possess room-temperature ferromagnetism on their own, they are widely modified by researchers using the emerging strategies to engineer or modulate their intrinsic properties. This paper reviews recent enhancement approaches to induce magnetism in 2D TMDs, mainly using doping, vacancy defects, composite of heterostructures, phase modulation, and adsorption, and also by electron irradiation induction, O plasma treatment, etc. On this basis, the produced effects of these methods for the introduction of magnetism into 2D TMDs are compressively summarized and constructively discussed. For perspective, research on magnetic doping techniques for 2D TMDs materials should be directed toward more reliable and efficient directions, such as exploring advanced design strategies to combine dilute magnetic semiconductors, antiferromagnetic semiconductors, and superconductors to develop new types of heterojunctions; and advancing experimentation strategies to fabricate the designed materials and enable their functionalities with simultaneously pursuing the upscalable growth methods for high-quality monolayers to multilayers.

Snx-0MnxS nanomaterial based electrodes for future-generation supercapacitor and data storage devices

In In this article, Mn-doped Snx-0MnxS (XMn = 0 – 9 %) were synthesized by solvothermal method and named MN1, MN2, MN3, MN4, MN5 and MN6 nanoparticles (NPs), respectively. The X-ray diffraction confirmed the single-phase orthorhombic crystal structure of MN1, MN2, MN3, MN4, MN5 and MN6 NPs. The FT-IR results showed a slight shift of the Sn-S stretching vibration towards the lower wavenumber from MN2 to MN5 NPs. The ball-like spherical shapes were observed in SEM and TEM images. The XPS spectrum of MN2 NPs confirms the binding energies of Sn, S, and Mn. EDX spectrum confirms the Sn, S and Mn elements in different ratios. To explore potential applications for supercapacitors (SCs), the nanospheres of MN1, MN2, MN3, MN4 and MN5 electrodes were used to check their Cyclic voltammograms (CV) and Galvanostatic charge-discharge (GCDs) measurements in a three electrode system in an aqueous solution of 2 M KOH. The increase in the specific capacitance values of MN1 electrode from 9 to 30 (F/g) with Mn dopant ratifies that external impurities have improved the electrochemical properties of pure SnS NPs and becomes an alternative source for energy storage devices. The magnetic performance recorded by VSM measurements demonstrated room temperature (RT) ferromagnetism and doping Mn ions induces alteration of ferromagnetism and therefore suggests potential applications in the data storage devices.

Growth, microstructure and magnetic properties of bixbyite structure ScFeO3: A comparative study between bulk and thin film

The growth, microstructure and magnetic property of both bulk and thin film types of ScFeO3 are studied. Results show that the mono-phase bixbyite structure bulk ScFeO3 can be obtained with sintering temperature above 1400 °C. The bulk ScFeO3 shows dominant antiferromagnetic property with an antiferromagnetic Neel temperature TN about -26 K. The epitaxial type of ScFeO3 thin film with bixbyite structure can be well grown on the SrTiO3(111) substrate. The magnetic property of ScFeO3 thin film is significantly different from that of bulk material which shows notable room temperature ferromagnetism with a saturation field below 0.4 T. The saturation magnetization MS, remanent magnetization Mr, coercivity Hc and of ScFeO3 film increase with decreasing temperature with maximum values of MS = 5.1 emu/cc, Mr = 1.5 emu/cc, and Hc = 29 mT at 5 K. The ferromagnetism of ScFeO3 thin film should be caused by the interface mismatch strain at film/substrate interface. This further proves that ferromagnetism of ScFeO3 can be stabilized with microstructure engineering including strain, which enable multifunctional properties of this material.

External Fields Assisted Highly Efficient Oxygen Evolution Reaction of Confined 1T-VSe2 Ferromagnetic Nanoparticles.

As a clean and effective approach, the introduction of external magnetic fields to improve the performance of catalysts has attracted extensive attention. Owing to its room-temperature ferromagnetism, chemical stability, and earth abundance, VSe2 is expected to be a promising and cost-effective ferromagnetic electrocatalyst for the accomplishment of high-efficient spin-related OER kinetics. In this work, a facile pulsed laser deposition (PLD) method combined with rapid thermal annealing (RTA) treatment is used to successfully confine monodispersed 1T-VSe2 nanoparticles in amorphous carbon matrix. As expected, with external magnetic fields of 800 mT stimulation, the confined 1T-VSe2 nanoparticles exhibit highly efficient oxygen evolution reaction (OER) catalytic activity with an overpotential of 228mV for 10mA cm-2 and remarkable durability without deactivation after >100h OER operation. The experimental results together with theoretical calculations illustrate that magnetic fields can facilitate the surface charge transfer dynamics of 1T-VSe2 , and modify the adsorption-free energy of *OOH, thus finally improving the intrinsic activity of the catalysts. This work realizes the application of ferromagnetic VSe2 electrocatalyst in highly efficient spin-dependent OER kinetics, which is expected to promote the application of transition metal chalcogenides (TMCs) in external magnetic field-assisted electrocatalysis.

Magnetic supercapacitors: Charge storage mechanisms, magnetocapacitance, and magnetoelectric phenomena

Pseudocapacitive (PC) materials are under investigation for energy storage in supercapacitors, which exhibit exceptionally high capacitance, good cyclic stability, and high power density. The ability to combine high electrical capacitance with advanced ferrimagnetic or ferromagnetic properties in a single material at room temperature opens an avenue for the development of advanced magnetically ordered pseudocapacitive (MOPC) materials. This review covers materials science aspects, charge storage mechanisms, magnetocapacitance, and magnetoelectric (ME) phenomena in MOPC materials. Recent studies demonstrate high PC properties of advanced ferrimagnetic materials, such as spinel ferrites and hexagonal ferrites. Of particular importance is the discovery of PC properties of perovskite-type manganites, which exhibit room temperature ferromagnetism and giant negative magnetoresistance. The coupling of high capacitance and magnetization in MOPC provides a platform for strong ME interactions. Various strategies are used for manipulation of electrical capacitance/magnetization of MOPC by a magnetic field/electrode potential. Magnetocapacitance studies show significant increase in capacitance of MOPC under the influence of a magnetic field. Moreover, the application of a magnetic field results in enhanced energy density and power density, reduction of resistance, and improvement of cyclic stability. Such findings offer a potential of a breakthrough in the development of advanced supercapacitors. High magnetocapacitance and ME phenomena are linked to the influence of magnetic fields on electrolyte diffusion, structure of electrical double layer, charge transfer resistance, and variation of conductivity and magnetization of MOPC materials, which facilitate charge/discharge behavior. Various applications of ME effect in MOPC are discussed. Moreover, advantages of magnetocapacitive MOPC are described for applications in electronic and spintronic devices, supercapacitors, and devices for magnetically enhanced capacitive deionization of water.

Impact of electrons spin on ferromagnetism and thermoelectric properties of BaFe2(S/Se/Te)4 for spintronic and green energy applications

Spintronic is an emerging field of advanced technology that controls the spin of electrons to transfer, handle, and store data simultaneously at a very fast rate. To improve it further, we have systematically studied the electronic behavior, ferromagnetism, and thermoelectric characteristics of BaFe2(S/Se/Te)4 spinel's. The optimization analysis shows the ferromagnetic states release more energy as compared to the antiferromagnetic states. Therefore, the studied compounds are existing in ferromagnetic states. The Heisenberg model is employed to calculate the spin polarization and Curie temperature to confirm above room temperature ferromagnetism. Furthermore, the nature of ferromagnetism, density of states, band structures, exchange constants and exchange energies, hybridization, crystal field energy, and double exchange model are addressed briefly. Shifting of the magnetic moment from Fe to Ba and S/Se/Te sites reveals that ferromagnetism is credited to the spin of electrons rather than the clustering of magnetic ions (Fe). Moreover, the thermoelectric parameters like Seebeck coefficient, conductivities, and power factor for spin-up (↑) and spin-down (↓) are explored to reveal how electron spin is affected by thermal parameters and for energy harvesting.

Structural, optical and magnetic characteristics of iron doped zinc oxide thin films

Zn1-xFexO films with x = 0, 5, 10, 15 and 20 at.% were prepared under high vacuum by the electron beam gun evaporation. The impact of Fe doping concentration on the films' structural, optical and magnetic characteristics has been taken into account. The patterns of XRD for all films at various Fe concentrations showed wurtzite-type structures. The results show that the size of nano-films reduces from 24 nm (0%) to 11 nm (0.20%) with elevating Fe content, which is owing to the difference between the ionic radii of Zn and Fe. Peaks associated with the elements to be seen were visible in the XPS spectra of undoped and 10% Fe-doped ZnO nanoparticles produced by the precipitation process: zinc (Zn), iron (Fe), and oxygen (O). The optical constants (n, k) of the Zn1-xFexO films were obtained by the SE measurements by an ellipsometric model, allowing for the verification of the Fe3+ ions in Fe-doped ZnO. With the addition of Fe, the energy band gap decreased from 3.44 eV to 3.28 eV. M-H measurements revealed room-temperature ferromagnetism in Fe-doped ZnO thin film. As the Fe concentration rises, the magnetization increases until it reaches a concentration of 15%, at which point it starts to decrease. This decrease in magnetization was attributable to the spinel phase, which was seen in the XRD spectra. These findings imply that Fe-doped ZnO is a highly suggested material for the creation of spintronic and optoelectronic devices.

Nonreciprocal Phonon Propagation in a Metallic Chiral Magnet.

The phonon magnetochiral effect (MChE) is the nonreciprocal acoustic and thermal transports of phonons caused by the simultaneous breaking of the mirror and time-reversal symmetries. So far, the phonon MChE has been observed only in a ferrimagnetic insulator Cu_{2}OSeO_{3}, where the nonreciprocal response disappears above the Curie temperature of 58K. Here, we study the nonreciprocal acoustic properties of a room-temperature ferromagnet Co_{9}Zn_{9}Mn_{2} for unveiling the phonon MChE close to room temperature. Surprisingly, the nonreciprocity in this metallic compound is enhanced at higher temperatures and observed up to 250K. This clear contrast between insulating Cu_{2}OSeO_{3} and metallic Co_{9}Zn_{9}Mn_{2} suggests that metallic magnets have a mechanism to enhance the nonreciprocity at higher temperatures. From the ultrasound and microwave-spectroscopy experiments, we conclude that the magnitude of the phonon MChE of Co_{9}Zn_{9}Mn_{2} mostly depends on the Gilbert damping, which increases at low temperatures and hinders the magnon-phonon hybridization. Our results suggest that the phonon nonreciprocity could be further enhanced by engineering the magnon band of materials.

Structural, optical, XPS, and magnetic properties of Sn–O nanoparticles

Sn–O nanoparticles ranging in average particle sizes from 13 to 420 nm have been prepared by levitation-jet aerosol synthesis through condensation of tin vapor in a mixed flow of inert gases and air/oxygen. XRD established the presence of mixed-phase of Sn, SnO, and SnO2 components in the nanoparticles. During optical measurements, the redshift of bandgaps was discovered in nanoparticles with SnO2 content <80% and blue shift in nanoparticles with SnO2 content >80%. The results indicate that the nanoparticles exhibit room-temperature ferromagnetism. The maximum net saturation magnetization observed in the studied nanoparticles is ≈ 7 memu/g near a Sn/O molar ratio of ≈0.58. Moreover, an excess magnetic contribution, either as paramagnetic or as diamagnetic susceptibility, has been observed. Raman studies found the presence of small amounts of Sn3O4 or Sn2O3 phases in the nanoparticles. The presence of oxygen vacancies in the nanoparticles was established by XPS. Their density increase accompanies by the saturation magnetization enhancement. We propose that the presence of definite localized states, like interacting and non-interacting vacancies on the Sn/SnO and SnO/SnO2 interfaces, is responsible for the observed magnetic phenomena.

Room Temperature Ferromagnetism and Enhanced Band Gap Values in N Co-doped Cr: CdS Nanoparticles for Spintronic Applications

Room Temperature Ferromagnetism and Enhanced Band Gap Values in N Co-doped Cr: CdS Nanoparticles for Spintronic Applications