Intrinsic Room Temperature Ferromagnetism Research Articles

Scaling study of the magnetic entropy change in room-temperature ferromagnet Cr3Te4

The intrinsic room-temperature ferromagnetism, stability in air, and easy tunability make chromium telluride Cr3Te4 a material with great promise for application in spintronics. This study investigates the magnetic entropy change (ΔSM) associated with critical exponents of Cr3Te4 single crystal. Temperature-dependent ΔSM suggests a drastic entropy change caused by the transition, the parameters of which show field-dependent power-law behaviors. Fitting the ΔSM(T,H) parameters yields critical exponents α=0.056(9), β=0.365(4), γ=1.212(3), δ=4.318(1), and Δ=1.562(5) for H//ab, while α=−0.077(3), β=0.369(6), γ=1.338(1), δ=4.620(6), and Δ=1.689(2) for H//c. The universality principle allows the ΔSM(T,H) to be scaled onto a single universal curve independent of external field. The direction-dependent differing critical exponents imply anisotropic magnetic couplings in Cr3Te4, which reveal a magnetic interaction of the 3D-Ising type for H//ab while a 3D-XY one for H//c. This work is beneficial for understanding the intrinsic and anisotropic room-temperature ferromagnetism in CrxTey family.

Turning Nonmagnetic Two-Dimensional Molybdenum Disulfides into Room-Temperature Ferromagnets by the Synergistic Effect of Lattice Stretching and Charge Injection.

Exploring two-dimensional (2D) room-temperature magnetic materials in the field of 2D spintronics remains a formidable challenge. The vast array of nonmagnetic 2D materials provides abundant resources for exploration, but the strategy to convert them into intrinsic room-temperature magnets remains elusive. To address this challenge, we present a general strategy based on surface halogenation for the transition from nonmagnetism to intrinsic room-temperature ferromagnetism in 2D MoS2 based on first-principles calculations. The derived 2D halogenated MoS2 are half-semimetals with a high Curie temperature (TC) of 430-589 K and excellent stability. In-depth mechanistic studies revealed that this marvelous nonmagnetism-to-ferromagnetism transition originates from the modulation of the splitting as well as the occupation of the Mo d orbitals by the synergy of lattice stretching and charge injection induced by the surface halogenation. This work establishes a promising route for exploring 2D room-temperature magnetic materials from the abundant pool of 2D nonmagnetic counterparts.

Two-dimensional HfCr2N4 semiconductor with intrinsic room-temperature ferromagnetism and enhanced conductivity via electrostatic doping

Two-dimensional semiconductors with room-temperature intrinsic ferromagnetism and superior conductivity are crucial components for low-dimensional semiconductor spintronic devices. Based on density functional theory and Boltzmann transport theory, we investigate the electromagnetic and transport properties of the HfCr2N4 monolayer and modulate these properties via electrostatic doping. The HfCr2N4 monolayer is an intrinsic ferromagnetic semiconductor with a narrow band gap of 0.18 eV. The notably high Curie temperature of 719 K is highly desired for the practical applications of two-dimensional ferromagnetic materials. Under electrostatic doping, the HfCr2N4 monolayer maintains its ferromagnetic ground state, easy magnetization xy-plane, and high Curie temperature. Interestingly, owing to the narrow band gap of the HfCr2N4 monolayer, a significant enhancement in conductivity is observed at lower carrier doping concentrations, leading to a transition from a semiconductor to a half-metal. These unique features can be utilized to represent binary states ‘0’ and ‘1’. Our results indicate that the HfCr2N4 monolayer emerges as an ideal candidate for dual-gate field effect transistors.

Prediction of intrinsic room-temperature ferromagnetism in two-dimensional CrInX2 (X = S, Se, Te) monolayers.

Herein, using density functional theory, novel two-dimensional (2D) CrInX2 (X = S, Se, Te) structures are predicted to be practical ferromagnetic (FM) semiconductors. Phonon vibrations and molecular dynamics simulations verified their structural and thermodynamic stability. Sizable fully spin-polarized band gaps of 1.03 and 0.69 eV are found for CrInS2 and CrInSe2, while CrInTe2 exhibits half-metallic band nature (at 0 K with a perfect lattice). The high magnetic anisotropy energies are responsible for their long-range spin polarization. The Curie temperatures (Tc) are estimated to be 347, 397 and 447 K for CrInS2, CrInSe2 and CrInTe2, respectively, all well above the room-temperature. The high Tc originates from unusual FM direct exchange, the efficient super-exchange coupling between neighboring Cr eg-orbitals with zero virtual exchange gaps and the presence of dual Cr-X-Cr super-exchange channels. Our systematic study of the CrInX2 monolayer suggests that it could be a promising material for spintronics applications.

Electronic spin resonance study of room-temperature ferromagnet cr[formula omitted]te[formula omitted

Chromium telluride Cr3Te4 with intrinsic room-temperature ferromagnetism has substantially practical application in spintronics. In this work, the microwave response of Cr3Te4 single crystal is investigated by the electronic spin resonance (ESR) with the magnetic field applied along various directions. Two resonance lines are observed for both H//ab and H//c, which are suggested to result from ferromagnetic (FM) and antiferromagnetic (AFM) fluctuations respectively. The angle-dependent ESR spectra show considerable anisotropy, with a strong microwave response for H//ab and a weak microwave response for H//c. The analysis of the ESR spectra reveals the coexistence of FM and AFM fluctuations in this system. Moreover, this anisotropic microwave response in single crystal Cr3Te4 could benefit the microwave-based spintronic device.

Two-Dimensional Iron Silicide (FeSix) Alloys with Above-Room-Temperature Ferromagnetism.

Two-dimensional (2D) materials with intrinsic room-temperature ferromagnetism have gathered tremendous interest as promising candidates for next-generation spintronics. Here, on the basis of first-principles calculations, we report a family of stable 2D iron silicide (FeSix) alloys via dimensional reduction of their bulk counterparts. Our results demonstrate that 2D Fe4Si2-hex, Fe4Si2-orth, Fe3Si2, and FeSi2 nanosheets are lattice-dynamically and thermally stable, confirmed by the calculated phonon spectra and Born-Oppenheimer dynamic simulation up to 1000 K. 2D FeSix nanosheets are ferromagnetic metals with estimated Curie temperatures ranging from 547 to 971 K due to strong direct exchange interaction between Fe sites. In addition, the electronic properties of 2D FeSix alloys can be maintained on silicon substrates, providing an ideal platform for spintronics applications in the nanoscale.

Two-dimensional Janus SVAN2 (A = Si, Ge) monolayers with intrinsic semiconductor character and room temperature ferromagnetism: tunable electronic properties via strain and an electric field.

In the context of developing next-generation information technology, two-dimensional materials with inherent ferromagnetism, a Curie temperature above room temperature, and significant magnetic anisotropy hold great promise. In this work, we employed first-principles calculations to investigate a novel two-dimensional Janus structure, namely SVAN2 (A = Si, Ge). Our findings reveal that these structures are not only dynamically and thermally stable, but also exhibit semiconductor properties alongside their ferromagnetic states. The Janus SVSiN2 monolayer exhibits an in-plane easy axis, while the SVGeN2 monolayer shows an out-of-plane easy axis, both characterized by a significant magnetic anisotropy energy (129 and 172 μeV, respectively). Notably, through Monte Carlo simulation, we found that the Curie temperature of the SVSiN2 monolayer is 330 K, which is higher than room temperature. Finally, by applying biaxial strain and an external electric field, we successfully regulated the electronic properties of the SVAN2 (A = Si, Ge) monolayers, enabling a transition from semiconductor to half-metallic behavior. These remarkable electronic and magnetic properties make the Janus SVAN2 (A = Si, Ge) monolayers promising candidate materials for spin electron applications.

Ferromagnetism of MnO anchored on graphene with N dopant

MnO is a well-known antiferromagnetic transition mental oxide with a wide band gap, the lack of intrinsic ferromagnetism limits its applications in spintronics. Hence, in order to expand the application field of MnO and especially explore the existence of ferromagnetism, we experimentally achieve the N-doped MnO anchored graphene. As is expected, the MnO-based samples exhibit obvious intrinsic room temperature ferromagnetism, which is dependent on the N dopant concentration. Further, density functional theory (DFT) results reveal that the spontaneous magnetization comes from the ferromagnetic double-exchange interaction between Mn atoms with the aid of N dopants.

Effects of substitutional Fe and oxygen vacancies on room temperature ferromagnetism of Fe-doped In2O3 dilute magnetic nanowires

The magnetic behavior and origin of dilute magnetic nanowires are critical for further development and application of nanoscale spintronic devices. In this work, the Fe doping into single-crystalline In 2 O 3 nanowires are fabricated using chemical vapor deposition (CVD) method to research these problems based on theoretical and experimental analysis. The XRD, XPS, TEM and XAS results show that the deposited Fe-doped In 2 O 3 nanowires possess the cubic bixbyite structure and the doped Fe ions substitute for the In sites of In 2 O 3 lattice with +2 and + 3 mixed valences. The PL results prove the existence of single ionized oxygen vacancies as well as the defect complexes of donor (oxygen vacancy)-acceptor (Fe impurity) pairs. The intrinsic room temperature ferromagnetism can be observed for the Fe-doped In 2 O 3 nanowires and the saturation magnetization largely enhance with Fe doping. The first principles calculations show that the introducing of oxygen vacancy defects can cause strong hybridization between Fe 3d and O 2p orbitals at the Fermi level, resulting in the transition from antiferromagnetic to ferromagnetic coupling between the Fe ions. These results open up the possibilities for exploring spin-electronic devices. • Effects of Fe doping on local structure, optical and magnetic properties of Fe-doped In 2 O 3 nanowires are studied. • The doped Fe ions substitute for the In sites of In 2 O 3 lattice with +2 and + 3 mixed valences. • Single ionized oxygen vacancies and the defect complexes of donor -acceptor pairs can be observed. • Introducing of oxygen vacancies results in the transition from antiferromagnetic to ferromagnetic coupling between Fe ions.

Linear, non-linear optical properties and magnetic studies of spray pyrolysis nanocrystalline Sn1-xCoxO2 films for multifunctional optoelectronic and spintronic applications

Abstract In this paper, the structural, morphological, linear & non-linear optical, and magnetic properties of spray pyrolysis nanostructured Sn1-xCoxO2 thin films (0 ≤ x ≤ 0.08) were studied employing X-ray diffraction (XRD), atomic force microscope (AFM), spectrophotometric, and vibrating sample magnetometer (VSM) techniques, respectively. A tetragonal type structure was observed for films without any sign of impurities. XRD with Rietveld refinement analysis further revealed an increase in lattice parameters and unsystematic changes in crystallite size. AFM micrograph analysis shows that the surface roughness and root mean square roughness of the film are improved with increasing Co doping. Moreover, the spectrophotometry results indicate a direct optical transition for the film with an energy band gap reduces from 3.8 eV (x = 0) to 3.34 eV (x = 0.07) due to the rise in structural disorder and the increase in the density of localized states. The optical constants are calculated from the light transmission spectrum using the envelope method of Swanepoel. It is seen that the overall behavior of the refractive index n(λ) and extinction coefficient k(λ) increase with increasing of Co content. The dispersive oscillator parameters estimated from the single-oscillator Wemple–DiDomenico model were used to determine the non-linear optical parameters, such as the third-order non-linear optical susceptibility χ(3) and non-linear refractive index n2. Finally, intrinsic room temperature ferromagnetism is observed, which is interpreted based on the bound magnetic polarons model. In conclusion, Co doping in SnO2 host semiconductor nanocrystalline films enhances their optical and magnetic characteristics, making it a potential candidate for multifunctional applications like optoelectronics and spintronics devices.

Morphology-Tunable Synthesis of Intrinsic Room-Temperature Ferromagnetic γ-Fe2O3 Nanoflakes.

Intrinsic two-dimensional (2D) magnetic materials with room-temperature ferromagnetism and air stability are highly desirable for spintronic applications. However, the experimental observations of such 2D or ultrathin ferromagnetic materials are rarely reported owing to the scarcity of these materials in nature and for the intricacy in their synthesis. Here, we report a successful controllable growth of ultrathin γ-Fe2O3 nanoflakes with a variety of morphologies tunable by the growth temperature alone using a facile chemical vapor deposition method and demonstrate that all ultrathin nanoflakes still show intrinsic room-temperature ferromagnetism and a semiconducting nature. The γ-Fe2O3 nanoflakes epitaxially grown on α-Al2O3 substrates take a triangular shape at low temperature and develop gradually in lateral size, forming eventually a large-scale γ-Fe2O3 thin film as the growth time increases due to a thermodynamic control process. The morphology of the nanoflakes could be tuned from triangular to stellated, petaloid, and dendritic crystalloids in sequence with the rise of precursor temperature, revealing a growth process from thermodynamically to kinetically dominated control. Moreover, the petaloid and dendritic nanoflakes exhibit enhanced coercivity compared with the triangular and stellated nanoflakes, and all the nanoflakes with diverse shapes possess differing electrical conductivity. The findings of such ultrathin, air-stable, and room-temperature ferromagnetic γ-Fe2O3 nanoflakes with tunable shape and multifunctionality may offer guidance in synthesizing other non-layered magnetic materials for next-generation electronic and spintronic devices.

Tunable ferromagnetic ordering in phosphorus adsorbed ReS2 nanosheets

Layered transition metal dichalcogenides (TMDs) are considered as promising materials for electronic, optoelectronic and spintronic devices due to their outstanding properties. Herein, based on rhenium disulfide (ReS2) nanosheets, we realized the intrinsic room temperature ferromagnetism with the adsorption of P adatoms (P-ReS2). Experiments indicate that the saturation magnetization (Ms ) can be tuned by the P ratios, where the maximum Ms can reach up to 0.0174 emu g−1. Besides, density functional theory (DFT) calculation results demonstrate that the strong hybridization between Re d and P p orbitals is the main reason of inducing ferromagnetism in P-ReS2 system. This work provides a novel method to engineer the magnetism of TMDs, endowing them with the possibility of spintronic applications.

Tunable valley polarization, magnetic anisotropy and dipole moment for layered Janus 2H–VSSe with intrinsic room temperature ferromagnetism

Effects of strain, interlayer coupling and electric field on the valley polarization, magnetocrystalline anisotropy and dipole moment of layered Janus 2H–VSSe are systematically investigated by first-principles calculations. A unique V 3 d1 electronic configuration and strong electron coupling interaction guarantee the stable in-plane ferromagnetic ground states with Tc of 512 K. By considering spin-orbit coupling (SOC) and exchange interaction based on the effective Hamiltonian k•p model, a large valley splitting of 94.8 meV is observed, which is mainly contributed by the spontaneous magnetic exchange field and not SOC effect. Under various bi-axis strains, Janus 2H–VSSe monolayer still maintains intrinsic in-plane ferromagnetism, but exhibits tunable valley polarization and magnetocrystalline anisotropy, which are associated with the in-plane dx2-y2/dxy orbitals of V atoms. Importantly, stacking patterns can influence the spatial inversion symmetry and further alter the valley polarization for the layered Janus 2H–VSSe. Applied external electric-field can effectively control intrinsic built-in electric-field by charge redistribution in the vertical direction, which can remarkably change the dipole moments and slightly adjust the valley polarization. The layered Janus 2H–VSSe possesses intrinsic ferromagnetism, robust valley-contrasting physics and outfield-dependent dipole moment, making them competitive materials for practical applications in spin-valleytronics, optoelectronics and piezoelectric sensor.

Proximity-induced ferromagnetism and chemical reactivity in few-layer VSe2 heterostructures

Among Transition-Metal Dichalcogenides, mono and few-layers thick VSe2 has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of Fe/VSe2 heterostructure by combining element sensitive absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk VSe2 do not show any signature of an intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the Fe/VSe2 interface and its relation with interfacial magnetic coupling.

Tuned optical and magnetic properties of Ce3+ doped SnS2 quantum dots

Magnetic semiconductor materials have been highly desired for spintronic applications in the past few years. Doping is an effective method to manipulate the magnetic and optical characteristics of non-magnetic semiconducting materials. Tin disulfide (SnS2), as a wide bandgap layered semiconductor, is a promising material in many fields, especially in spintronic devices. In this work, we propose a facile chemical reaction method to synthesize SnS2:Ce3+ quantum dots (QDs), and the optical and magnetic characteristics of the as-obtained samples are fully investigated. The results show that the substitutional Ce3+ dopants introduce robust intrinsic room-temperature ferromagnetism in the SnS2 semiconductor and the doping concentration of Ce3+ ions effectively influences the optical bandgap and photoluminescence properties of the samples. Furthermore, the theoretical calculations using VASP software indicate that ferromagnetism mainly comes from the exchange interaction between 4f and 5d orbitals of the Ce dopant. These findings demonstrate that the doping dependent optical and magnetic characteristics of the SnS2:Ce3+ QD material can enable its application in electronics and spintronics.

Effect of Ho dopant on the ferromagnetic characteristics of MoS2 nanocrystals.

Transition-metal dichalcogenides (TMDs) have been widely studied for decades in the spintronic device application. However, designing and tuning the magnetic properties of molybdenum disulphide (MoS2) is still a great challenge. In this work, the as-synthesized MoS2:Ho3+ nanocrystals exhibit robust room-temperature ferromagnetism and the ferromagnetism is controlled by different doping concentrations of Ho3+ ions. The maximum saturation magnetization is 0.055 emu g-1. Based on first-principles calculations, the intrinsic ferromagnetic and the changed electronic properties are introduced by Ho3+ doping. The as-obtained MoS2:Ho3+ nanocrystals with intrinsic ferromagnetism may be a potential candidate in the spintronics field and this approach may be employed in the magnetic applications of other TMDs.

Re doping induced 2H-1T phase transformation and ferromagnetism in MoS2 nanosheets

In this paper, Re-doped MoS2 nanosheets were synthesized by a facile hydrothermal reaction and an annealing process. Through structural characterization, it was observed that the doping of Re could lead to 2H-1T transformation in both the Re and Mo coordinating structures, and the 1T ratios of Mo and Re atoms increased with the Re-doping concentration. Hysteresis loops demonstrated intrinsic room temperature ferromagnetism in the Re-doped MoS2 nanosheets, and the value of saturated magnetization reached 8 memu/g when the doping concentration of Re was 17.12 at. %. The magnetic properties resulted from the increasing net magnetic moments of Re atoms and 1T-coordinated Mo atoms. Additionally, the 1T-incorporated 2H structure and magnetism were thermally stable in these samples. These results explored a new path for MoS2 nanosheets to be applied in spintronic devices in the future.

Defect-induced room temperature ferromagnetism in silicon carbide nanosheets

Silicon carbide (SiC) nanosheets with different sizes and thickness were synthesized by a liquid exfoliation method by varying the exfoliating time in the N, N-dimethylformamide organic solvent. During the exfoliating time increasing from 4 to 16 h, the size of the SiC nanosheets decreases gradually from 500 to 200 nm, and the thickness decreases from 9 to 3.5 nm. Results showed that all prepared SiC nanosheets show intrinsic room temperature ferromagnetism, which is greatly different to the diamagnetism nature of virgin bulk SiC. Moreover, the saturation magnetization of the SiC nanosheets increases monotonously from 0.005 to 0.018 emu/g as the size and thickness decrease. Further studies via transmission electron microscopy, superconducting quantum interference device, and electron spin resonance revealed that the origin of the ferromagnetism in SiC nanosheets might be attributed to the defects with carbon dangling bond on the surface of nanosheets.

Oxygen vacancies driven size-dependent d0 room temperature ferromagnetism in well-dispersed dopant-free ZnO nanoparticles and density functional theory calculation

This paper reports the intrinsic size-dependent d0 room-temperature ferromagnetism in dopant-free ZnO nanoparticles, which were fabricated by thermal decomposition route. The size of ZnO nanoparticles can be controlled by simply tuning the amount ratio of solvent. Transmission electron microscope shows that the ZnO nanoparticles are well-dispersed without aggregation. Magnetic measurement suggests that the undoped ZnO nanoparticles show room temperature ferromagnetic characteristic, which is sensitive with the particle size. Photoluminescence spectra and X-ray photoelectron spectroscopy measurements elucidate that the relative concentration of oxygen vacancies increase as the particle sizes decrease, leading to long-range ferromagnetic ordering in the undoped ZnO nanoparticles. A correlation among the particle size, ferromagnetism and relative concentration of oxygen vacancies is established, which demonstrates that oxygen vacancies play a key role to induce ferromagnetic ordering. Furthermore, density functional theory calculation demonstrates that the oxygen vacancies in ZnO with positive charge trapping can induce polar-magnetization which is stable states. The correlation between experiments and simulations suggests that the ferromagnetic behavior in diluted magnetic semiconductors can be conveniently manipulated by tuning the surface-volume ratio of nanostructures and surface defects, which is of great significance to understand and explore novel diluted magnetic semiconductors.

Transparent magnetic semiconductor with embedded metallic glass nano-granules

One central material issue in spintronics is the search for high temperature (above room temperature) magnetic semiconductors. We report on the formation of a transparent magnetic semiconductor with embedded ferromagnetic metallic glass nano-granules, showing a Curie temperature of ~600K. Soft X-ray magnetic circular dichroism data verify its intrinsic room-temperature ferromagnetism. Owing to the unique structure of ferromagnetic nano-granules embedded in the host magnetic semiconductor, additional interfacial exchange anisotropy emerges and stabilizes the ferromagnetism. The magnetotransport measurements of the amorphous nanocomposite indicate that its anomalous Hall effect is dominated by the extrinsic mechanism of the side-jump due to the spin-dependent impurity.