Intrinsic Magnetic Material Research Articles

The intrinsic ferromagnetic half-metals with high Curie temperature of tetragonal XCrS4 (X=Ti, Zr) monolayer

Two-dimensional intrinsic magnetic materials with a high Curie temperature (TC) and 100% spin-polarization are highly desirable for creating spintronic devices. In this work, the electronic structure and intrinsic magnetism of XCrS4 (X = Ti, Zr) monolayers are predicted by using first-principles calculations. XCrS4 (X = Ti, Zr) monolayer materials exhibit excellent dynamical, thermal, and dynamically stable stability and small binding energy. The band structures show that XCrS4 (X = Ti, Zr) monolayers are intrinsic ferromagnetic (FM) half-metals with wide half-metallic gaps. Monte Carlo simulations based on the Heisenberg model are used to estimate the Curie temperature (TC) of the TiCrS4 (73 K) and ZrCrS4 (216 K) monolayers. The magnetic performances can be significantly modulated by strain; the TiCrS4 monolayer can undergo FM to antiferromagnetic phase transition under certain uniaxial and biaxial strains. The results indicate that the intrinsic half-metals with higher TC and controllable magnetic properties make XCrS4 (X = Ti, Zr) monolayers enrich the application of nanoscale spintronic devices.

Robust Ferromagnetism in Hexagonal Honeycomb Transition Metal Nitride Monolayer.

Two-dimensional intrinsic magnetic materials with high Curie temperature are promising candidates for next-generation spintronic devices. In this work, we design two kinds of two-dimensional transition metal nitrides, VN2 and FeN2, both with a hexagonal honeycomb lattice. Based on the formation energy, and phonon spectra calculations as well as the molecular dynamics simulations, their structural stability is demonstrated. Then, we determine the ferromagnetic ground states of VN2 and FeN2 monolayers through the energy calculations, and the Curie temperatures of 222 K and 238 K are estimated by solving the Heisenberg model using the Monte Carlo simulation method. Hence, the VN2 and FeN2 monolayers are demonstrated to be new two-dimensional ferromagnetic materials with high temperature ferromagnetism or large-gap half-metallicity.

Advancements in High‐Throughput Screening and Machine Learning Design for 2D Ferromagnetism: A Comprehensive Review

Abstract2D intrinsic magnetic materials possess unique physical properties distinct from bulk materials, providing an ideal research platform for the development of low‐dimensional spintronics. The traditional approach to developing new materials involves a “trial‐and‐error” method, which is inherently flawed due to long development cycles and high costs. In recent years, with the rapid improvement in computational power, the high throughput (HTP) first‐principles calculation based on density functional theory (DFT) and machine learning (ML) method have provided a highly effective means for the design of novel intrinsic ferromagnetic materials and the study of their magnetic properties. This article reviews the recent research progress in 2D ferromagnetic materials, with particular emphasis on the significant role played by HTP first‐principles calculations and ML in the exploration and fabrication of two‐dimension ferromagnetic (2DFM) materials. Finally, the future development and challenges of 2DFM materials are discussed.

Insight into the quantum anomalous Hall states in two-dimensional kagome Cr3Se4 and Fe3S4 monolayers.

To realize the quantum anomalous Hall (QAH) effect in two-dimensional (2D) intrinsic magnetic materials, which combines insulating bulk states and metallic edge channel states, is still challenging in experiment. Here, based on first-principles calculations, we predicted two stable kagome-latticed QAH insulators: Cr3Se4 and Fe3S4 monolayers, with the Chern number C = 1. It is found that both structures exhibit a large magnetic anisotropy energy and sizable band gaps, and a topological phase transition from C = -1 to C = 1 occurs when the magnetization orientation changes from the z-axis to the -z-axis. Remarkably, the non-trivial topological properties are robust against biaxial strains of up to ±6%. Furthermore, a variable high Chern number of C = 2 or C = 3 can be observed by stacking two or three layers of the QAH monolayer with an MoS2 insulator. Our results signify that such layered kagome materials can be promising platforms for exploring novel QAH physics.

Prediction of bipolar VSi2As4 and VGe2As4 monolayers with high Curie temperature and strong magnetocrystalline anisotropy

Recent studies have demonstrated that two-dimensional intrinsic magnetic materials with high Curie temperature $({T}_{\text{c}})$ and large magnetic anisotropy energy (MAE) are highly desirable for future spintronics. After careful investigations through density functional theory, bipolar ${\mathrm{VSi}}_{2}{\mathrm{As}}_{4}$ and ${\mathrm{VGe}}_{2}{\mathrm{As}}_{4}$ monolayers, with semiconductor valence and conduction band edges fully spin polarized in different spin directions, are demonstrated to be highly stable and have in-plane ferromagnetism (FM) with large MAE of $\ensuremath{\sim}5.5$ meV. The FM interaction is found to be dominated by the superexchange between d orbitals of V atoms through p orbitals of anions. More interestingly, ${T}_{\text{c}}$ is estimated to be $\ensuremath{\sim}900$ K through Monte Carlo simulation, which is significantly higher than room temperature. In addition, both MAE and ${T}_{\text{c}}$ can be substantially regulated and increased under biaxial strain and the transition from FM semiconductors to metals will occur. Our calculations and analyses indicate that ${\mathrm{VSi}}_{2}{\mathrm{As}}_{4}$ and ${\mathrm{VGe}}_{2}{\mathrm{As}}_{4}$ monolayers are ideal systems for the fundamental understanding of magnetic physics as well as building blocks for magnetoelastic applications, high-temperature, or/and gate-tunable spintronic nanodevices.

MNBr (M = Mo, Cr, V) monolayer: two-dimensional ferromagnetic half-metallic materials with high Curie temperature

Two-dimensional (2D) intrinsic magnetic materials with a high Curie temperature (T C ) and 100% spin-polarization are highly desirable for creating spintronic devices. In this work, the electronic structure and intrinsic magnetism of MNBr (M = Mo, Cr, V) monolayers are predicted by using first-principles calculations. The results show that MNBr (M = Mo, Cr, V) monolayers with GGA + U functionals are intrinsic ferromagnetic (FM) half-metals with wide half-metallic gaps. Monte Carlo simulations based on the Heisenberg model are used to estimate the T C of MoNBr, CrNBr and VNBr, which are 402 K, 673 K, and 120 K, respectively. The magnetic performances are significantly modulated by strain and carrier doping. Our results show that the intrinsic half-metals with a high T C and controllable magnetic properties make MNBr (M = Mo, Cr, V) monolayers potential for spintronic applications.

2D Magnetic Heterostructures and Emergent Spintronic Devices

AbstractThe discovery of 2D intrinsic magnetic materials with ultrathin structures and smooth surfaces has enabled the investigation of fundamental magnetism physics and creation of spintronic devices. By vertically stacking 2D magnetic materials with other magnetic or nonmagnetic materials, various magnetic heterostructures and spintronic devices can be developed. Recent progress in emergent 2D magnetic heterostructures and spintronic devices is reviewed. First, various typical 2D magnetic materials and methods for constructing and characterizing magnetic heterostructures are briefly introduced. Then, magnetic heterostructures composed of magnetic/nonmagnetic and magnetic/magnetic materials are summarized, and recent advances in spintronic devices fabricated using magnetic heterostructures and the device performance are presented. Finally, an outlook for the future development of 2D magnetic heterostructures and spintronic devices is presented.

Evolution of surface states of antiferromagnetic topological insulator MnBi2Te4 with tuning the surface magnetization

The interplay between magnetism and topologically non-trivial electronic states is an important subject in condensed matter physics. Recently, the stoichiometric intrinsic magnetic material MnBi2Te4 provides an ideal platform to study the magnetic topological phenomena, such as quantum anomalous Hall effect, axion insulator state, topological magnetoelectric effect. However, it is still controversial whether the topological surface state in the (111) plane is gapped or not. Here, we develop an effective method to study different surface magnetizations based on first-principles calculations. Then we investigate the band dispersions, the Fermi surfaces (FSs), the quasiparticle interferences (QPIs) and the spin texture of topological surface states of MnBi2Te4 with tuning the surface magnetization. We find that the surface magnetization has significant effects on the surface states. Our results also indicate that the symmetry breaking of FSs and QPIs may be a useful way to determine the possible surface magnetization of MnBi2Te4.

Valley-dependent topological phase transition and quantum anomalous valley Hall effect in single-layer RuClBr

Quantum anomalous valley Hall effect (QAVHE), which combines both the features of QAHE and AVHE, is both fundamentally intriguing and practically appealing, but is experimentally challenging to realize in two-dimensional (2D) intrinsic magnetic materials to date. Here, based on first-principles calculations with the density functional theory $+U$ approach, we predicted the electronic correlation-driven valley-dependent quantum phase transition from ferrovalley (FV) to half-valley-semiconductor (HVS) to QAVHE to HVS to FV phase in single-layer RuClBr. Remarkably, the QAVHE phase with an integer Chern number ($C=1$) and chiral spin-valley locking, which is induced by sign-reversible Berry curvature or band inversion between ${d}_{xy}/{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{{z}^{2}}$ orbitals, can achieve complete spin and valley polarizations for low-dissipation electronics devices. We also find that the electron valley polarization can be switched by reversing magnetization direction, providing a route of magnetic control of the valley degree of freedom. An effective $k\ifmmode\cdot\else\textperiodcentered\fi{}p$ model is proposed to clarify valley-dependent quantum phenomena. Additionally, electronic correlation has an important effect on the variations of the Curie temperature of single-layer RuClBr. These findings shed light on the possible role of correlation effects on valley-dependent physics in 2D materials and open alternative perspectives for multifunctional spin-valley quantum devices in valleytronics.

First principles study of 2D half-metallic ferromagnetism in Janus Mn2XSb (X = As, P) monolayers

Two-dimensional (2D) intrinsic magnetic materials have attracted much attention because of their fascinating physical properties. However, low Curie temperature TC and small magnetic anisotropy energy (MAE) limit their application prospects. Based on the density functional theory, we predict that Janus Mn2AsSb and Mn2PSb monolayers are 2D intrinsic ferromagnetic half-metals. Monte Carlo simulations suggest that the TC values of these monolayers are about 385 and 334 K, respectively. The Mn2AsSb and Mn2PSb monolayers exhibit large MAEs of 415.2 and 450.6 μeV per Mn, respectively. Their ferromagnetism is robust against biaxial strain in the range from −10% to 10%. An energy band calculation with the Heyd–Scuseria–Ernzerhof (HES06) functional indicates that the half-metallic spin bandgaps are about 1.00 and 0.81 eV and the bandgaps on the spin-down channel are 2.67 and 2.53 eV for Mn2AsSb and Mn2PSb monolayers, respectively. These exciting electronic and magnetic properties make Janus Mn2XSb (X = As, P) monolayers promising candidate materials for 2D spintronic devices.

Strain tunable intrinsic ferromagnetic in 2D square CrBr2

Two-dimensional intrinsic magnetic materials with high Curie temperature (Tc) coexisting with 100% spin polarization are highly desirable for realizing promising spintronic devices. In the present work, the intrinsic magnetism of monolayer square CrBr2 is predicted by using first-principles calculations. The monolayer CrBr2 is an intrinsic ferromagnetic half-metal with the half-metallic gap of 1.58 eV. Monte Carlo simulations based on the Heisenberg model estimate Tc as 212 K. Furthermore, the large compressive strain makes CrBr2 undergo ferromagnetic–antiferromagnetic phase transition when the biaxial tensile strain larger than 9.3% leads to the emergence of semiconducting electronic structures. Our results show that the intrinsic half-metal with a high Tc and controllable magnetic properties endow monolayer square CrBr2 as a potential material for spintronic applications.

Structure Engineering of 2D Materials toward Magnetism Modulation

2D magnetic materials have shown great potentials in fundamental research and spintronic devices. However, the discovered 2D magnetic materials are still limited and their monotonous magnetic properties cannot meet the needs of practical applications. Recently, the modulation of magnetism in 2D materials attracted tremendous attention, which can enrich the 2D magnetic material family and extend their application prospects. Structure engineering is one of the most effective ways to realize tunable 2D magnetic properties. Herein, the recent progress on 2D magnetism modulation via structure engineering is summarized. The basic theory of 2D magnetism is introduced at first. Then, the magnetism modulation by structure engineering is classified into two ways: inducing long‐range magnetic ordering into nonmagnetic materials and regulating the native magnetism of intrinsic magnetic materials. Moreover, recent progress on magnetism modulation by intercalation, chemical doping, defect engineering, and heterostructure construction is discussed in detail. Finally, the challenges and prospects in the future of 2D magnetism are also provided.

Recent progress on 2D magnets: Fundamental mechanism, structural design and modification

The two-dimensional (2D) magnet, a long-standing missing member in the family of 2D functional materials, is promising for next-generation information technology. The recent experimental discovery of 2D magnetic ordering in CrI3, Cr2Ge2Te6, VSe2, and Fe3GeTe2 has stimulated intense research activities to expand the scope of 2D magnets. This review covers the essential progress on 2D magnets, with an emphasis on the current understanding of the magnetic exchange interaction, the databases of 2D magnets, and the modification strategies for modulation of magnetism. We will address a large number of 2D intrinsic magnetic materials, including binary transition metal halogenides; chalogenides; carbides; nitrides; oxides; borides; silicides; MXene; ternary transition metal compounds CrXTe3, MPX3, Fe-Ge-Te, MBi2Te4, and MXY (M = transition metal; X = O, S, Se, Te, N; Y = Cl, Br, I); f-state magnets; p-state magnets; and organic magnets. Their electronic structure, magnetic moment, Curie temperature, and magnetic anisotropy energy will be presented. According to the specific 2D magnets, the underlying direct, superexchange, double exchange, super-superexchange, extended superexchange, and multi-intermediate double exchange interactions will be described. In addition, we will also highlight the effective strategies to manipulate the interatomic exchange mechanism to improve the Curie temperature of 2D magnets, such as chemical functionalization, isoelectronic substitution, alloying, strain engineering, defect engineering, applying electronic/magnetic field, interlayer coupling, carrier doping, optical controlling, and intercalation. We hope this review will contribute to understanding the magnetic exchange interaction of existing 2D magnets, developing unprecedented 2D magnets with desired properties, and offering new perspectives in this rapidly expanding field.

Atomic-orbital-free intrinsic ferromagnetism in electrenes

We report intrinsic ferromagnetism in monolayer electrides or electrenes, in which excess electrons act as anions. Our first-principles calculations demonstrate that magnetism in such electron-rich two-dimensional (2D) materials originates from the anionic electrons rather than partially filled d orbitals, which is fundamentally different from ferromagnetism found in other 2D intrinsic magnetic materials. Taking the honeycomb LaBr$_2$ (La$^{3+}$Br$^{-}_{2}\cdot e^{-}$) as an example, our calculations reveal that the excess electron is localized at the center of the hexagon, which leads to strong Stoner-instability of the associated states at the Fermi energy, resulting in spontaneous magnetization and formation of a local moment. The overlap of extended tails of the wave functions of these electrons mediates a long-range ferromagnetic interaction, contributing to a Curie temperature ($T_\textrm{c}$) of 235 K and a coercive field ($H_\textrm{c}$) of 0.53 T, which can be further enhanced by hole doping. The dual nature, localization and extension, of the electronic states suggests a unique mechanism in such magnetic-element-free electrenes as intrinsic 2D ferromagnets.

Temperature dependence of the magnetic properties of L1-FePt nanostructures and films

Hard magnetic L10-Fe51Pt49 thin films with out-of-plane texture and film thicknesses between 3 and 200 nm have been prepared on MgO(001) single crystalline substrates by co-sputtering and have been magnetically investigated by SQUID magnetometry at different temperatures ranging from 40 K up to the Curie temperature. The Curie temperature is found to be 660 K for film thicknesses down to 8 nm and decreases almost linearly for thinner films. For the whole ferromagnetic temperature range the intrinsic magnetic material parameters (saturation polarization Js, magnetocrystalline anisotropy constant K1, exchange constant A) and the coercivity μ0Hc are determined as a function of the film thickness. Furthermore the microstructural parameters are ascertained by analyzing the temperature dependence of the coercivity within the framework of micromagnetism leading to a deeper understanding of the magnetic reversal process.

Magnetocrystalline anisotropy constants, magnetic domain structure and intrinsic magnetic material parameters of Sm–Mn–Co system

Abstract Magnetic domain structures in Sm 11 Mn x Co 89− x ( x =20; 30) and Sm 13 Mn x Co 87− x ( x =10; 15; 20; 25) compunds were studied using the powder pattern method. The domain wall energy was determined from analysis of domain structure patterns and compared with other models. The following intrinsic magnetic material parameters of the studied magnets were determined: domain wall width δ B , critical single-domain radius D c and exchange constant A .

Magnetic Domain Structure and Intrinsic Magnetic Material Parameters of Ternary Intermetallic RMn2Ge2 Compounds (R ? La, Ce, Pr and Nd)

Applying a powder pattern method the magnetic domain structures of polycrystalline intermetallic RMn2Ge2 (where R ≡ La, Ce, Pr, Nd) compounds were studied. The domain structures observed are typical for uniaxial materials. The domain wall energy density γ was determined from analysis of domain structure patterns, using different models of the domain structure. The obtained values are used to determine the intrinsic magnetic material parameters: domain wall width δB, critical diameters of single domain particles Dc and exchange constants A.

Magnetic properties of the anisotropic FeAlC permanent magnet within the temperature range of 4.2 to 1100 K

The intrinsic magnetic material parameters of the FeAlC magnet are determined in the temperature range from 4.2 to 1100 K. It is shown that magnetization in this alloy is well described by the spin wave theory for temperatures 4.2 to 520 K. For temperatures between 520 and 720 K a narrow plateau in the magnetization plot is present. Similar temperature dependences of the coercive force Hc, the anisotropy field Ha, and the anisotropy constant K1 are observed. The analysis of the temperature dependence of the coercive field leads to the conclusion that the pinning model is valid for the temperature range 4.2 to 520 K. The temperature dependences of the domain wall energy γ, the domain wall width δB, and the critical diameter of single domain particles Dc are determined. Moreover, the distribution of grain orientations is determined and it is shown that the experimentally determined torque curve for the FeAlC magnet is a superposition of the torque originating from the magnetocrystalline anisotropy of K-carbide and α-ferrite.

Ab initio electron theory for hard-magnetic rare-earth-transition-metal intermetallics

For the development of new hard-magnetic materials a better understanding of the physical mechanisms which determine the intrinsic magnetic material parameters are of invaluable importance. In this review it is demonstrated that the modern ab initio electron theory yields a considerable help in this direction and may provide data on quantities which are hard to determine reliably by experiments. As an example, theoretical results are reported for the intrinsic magnetic material parameters (local magnetic moments, local magnetic hyperfine fields, crystal-field parameters and effective exchange interactions) of the series R2Fe14B (R = rare earth).

Magnetic Remanences in Migratory Birds

In connection with indications of the magnetic field detection in migratory birds, the measurements of magnetic remanences were carried out in both the migratory birds (Rustig Bunting and Reed Bunting) and the non-migratory birds (Siberian Meadow Bunting and Tree Sparrow) by means of SQUID magnetometer. Regardless of whether the species was migratory or not, neither heads nor neck musculatures indicated any presence of intrinsic magnetic materials related to the sensory mechanisms. The natural remanence and the induced remanence were of the orders of 10-8-10-7 e. m. u. and of 10-7-10-6 e. m. u. respectively. The magnetic sensor of birds for a compass reception is discussed.