Large Magnetocrystalline Anisotropy Energy Research Articles

CrP2Se6 monolayer: Two-dimensional intrinsic ferromagnetic half-metal with large magnetic anisotropy and high Curie temperature

Low Curie temperature (TC) and small magnetocrystalline anisotropy energy (MAE) are the main obstacle limiting the application of two-dimensional (2D) ferromagnetic (FM) materials. Here, by using first-principles calculations and Monte Carlo method, we predicted a 2D intrinsic FM CrP2Se6 monolayer with high TC and large MAE. The result shows that the TC of CrP2Se6 monolayer is about 440 K based on Monte Carlo simulations, and this monolayer possesses desired out-of-plane (z axis) easy magnetic axis with large MAE (∼1.2 meV/Cr). Interestingly, CrP2Se6 monolayer is intrinsically half-metallic with the spin filtering reaching 100 % and a wide spin gap of 3.09 eV under Heyd–Scuseria–Ernzerhof (HSE06) level. In addition, the dynamic, thermal, and mechanical stabilities of CrP2Se6 monolayer were confirmed by our phonon dispersion calculations, ab initio molecular dynamics simulations, and elastic constants, respectively. These outstanding magnetic properties make 2D CrP2Se6 monolayer a promising candidate for high efficiency spintronic devices.

Predicting layered itinerant magnetic Fe3SiSe2 with spontaneous valley polarization

Density functional theory calculations are performed to systematically investigate the electronic and magnetic properties of few-layer and bulk Fe3SiSe2 (FSS). We predict that the bulk FSS has a metallic ground state and a layered structure displaying intralayer ferromagnetic ordering and interlayer antiferromagnetic ordering. The itinerant magnetism in the FSS was determined by the Stoner criterion. Predictions of the absence of unstable phonon modes and a moderate cleavage energy of only 28.3 meV/Å2 suggest the possibility of stabilizing FSS in a monolayer form. The calculated spin–orbit coupling facilitates not only a large magnetocrystalline anisotropy energy, around 500 μeV/Fe, but also spontaneous valley polarization in odd-numbered layer systems. These systems have net magnetic moments as the magnetic moments of AFM-ordered layers are not fully compensated in the odd-numbered layer case and are predicted to show 2D metallic behaviors. The magnitude of the valley polarization in odd-numbered layered systems decreases from 18 meV with layer number but is absent in even-layered structures, thus showing an odd–even oscillation effect. Experimental realization of this bidimensional metallic magnet is, therefore, expected to widen the arena of two-dimensional materials that show exotic phenomena.

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.

Magnetic order and magnetic anisotropy in two-dimensional ilmenenes.

Iron ilmenene is a new two-dimensional material that has recently been exfoliated from the naturally occurring iron titanate found in ilmenite ore, a material that is abundant on the earth's surface. In this work, we theoretically investigate the structural, electronic and magnetic properties of 2D transition-metal-based ilmenene-like titanates. The study of magnetic order reveals that these ilmenenes usually present intrinsic antiferromagnetic coupling between the 3d magnetic metals decorating both sides of the Ti-O layer. Furthermore, the ilmenenes based on late 3d brass metals, such as CuTiO3 and ZnTiO3, become ferromagnetic and spin compensated, respectively. Our calculations which include spin-orbit coupling reveal that the magnetic ilmenenes have large magnetocrystalline anisotropy energies when the 3d shell departs from being either filled or half-filled, with their spin orientation being out-of-plane for elements below half-filling of 3d states and in-plane above. These interesting magnetic properties of ilmenenes make them useful for future spintronic applications because they could be synthesized as already realized in the iron case.

High curie temperature, large magnetocrystalline anisotropy energy and piezoelectricity in 2D tetrahedral VXCl (X = Te, Se, S) & VMSe2 (M = Al, Ga, In)

The ferromagnetic semiconducting materials with tetrahedral coordination structure have lower crystal field repulsion energy and variable structure, which would be beneficial to achieve high Curie temperature and multiferroics. Based on density functional theory calculations, the monolayer VXCl (X = Te, Se, S) and VMSe2 (M = Al, Ga, In) with tetrahedral coordination structure are predicted to be ferromagnetic semiconductors with high T c and large magnetocrystalline anisotropy. With the monolayer BiCrSe3 (T c above 400 K) being treated as the representative sample of octahedral materials, we reveal the disadvantages of two different coordination structures in 2D condition, namely tetrahedral and octahedral coordination, and find that modulation of bond angles is effective and feasible to enhance the magnetic exchange of tetrahedral materials. Moreover, the two series of predicted materials have favorable piezoelectric properties. Our work paves a feasible route for finding new low-dimensional ferromagnetic materials with excellent properties.

Compositional Dependence of Magnetocrystalline Anisotropy, Magnetic Moments, and Energetic and Electronic Properties on Fe-Pt Alloys.

This work reported the first-principles calculations for the compositional dependence of the energetic, electronic, and magnetic properties of the bimetallic Fe-Pt alloys at ambient conditions. These hybrid alloys have gained substantial attention for their potential industrial applications, due to their outstanding magnetic and structural properties. They possess high magnetocrystalline anisotropy, density, and coercivity. Four Fe-Pt alloys, distinguished by compositions and space groups, were considered in this study, namely P4/mmm-FePt, I4/mmm-Fe3Pt, Pm-3m-Fe3Pt, and Pm-3m-FePt3. The calculated heats of formation energies were negative for all Fe-Pt alloys, demonstrating their stability and experimentally higher formation probability. The P4/mmm-FePt alloy had the lowest magnetic moment, leading to durable magnetic hardness, which made this alloy the most suitable for permanent efficient magnets, and magnetic recording media applications. Moreover, it possessed a relatively large magnetocrystalline anisotropy energy value of 2.966 meV between the in-plane [100] and easy axis [001], suggesting an inside the plane isotropy.

Large magneto-optical effect and magnetic anisotropy energy in two-dimensional metallic ferromagnet Fe3GeTe2

The recent discovery of long-range magnetic orders in atomically thin semiconductors ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ and $\mathrm{Cr}{\mathrm{I}}_{3}$ as well as metal ${\mathrm{Fe}}_{3}\mathrm{Ge}{\mathrm{Te}}_{2}$ has opened up exciting opportunities for fundamental physics of two-dimensional (2D) magnetism and also for technological applications based on 2D magnetic materials. To exploit these 2D metallic magnets, the mechanisms that control their physical properties should be well understood. In this paper, based on systematic first-principles density functional theory calculations, we study the magnetic anisotropy energy (MAE) and magneto-optical (MO) effects of ferromagnetic multilayers [mono-, bi-, tri-, tetra-, and pentalayer] and bulk ${\mathrm{Fe}}_{3}\mathrm{Ge}{\mathrm{Te}}_{2}$ as well as their connections with the underlying electronic structures of the materials. Firstly, all the considered ${\mathrm{Fe}}_{3}\mathrm{Ge}{\mathrm{Te}}_{2}$ structures are found to prefer the out-of-plane magnetization and have gigantic MAEs of $\ensuremath{\sim}3.0$ meV/f.u. This gigantic perpendicular anisotropy results from the large magnetocrystalline anisotropy energy (MCE), which is ten times larger than the competing magnetic dipolar anisotropy energy. The giant MCEs are attributed to the large Te ${p}_{x,y}$ orbital density of states near the Fermi level and also to the topological nodal point just below the Fermi level at the K points in the Brillouin zone. Secondly, 2D and bulk ${\mathrm{Fe}}_{3}\mathrm{Ge}{\mathrm{Te}}_{2}$ also exhibit strong MO effects with their Kerr and Faraday rotation angles being $\ensuremath{\sim}1.{0}^{\ensuremath{\circ}}$ and $\ensuremath{\sim}100 \mathrm{deg}/\ensuremath{\mu}\mathrm{m}$ in the visible-light frequency region, respectively. The strong MO Kerr and Faraday effects are found to result from the large MO conductivity (or strong magnetic circular dichroism) in these ferromagnetic materials. In particular, the calculated MO conductivity spectra are one order of magnitude larger than that of ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$. The calculated MO conductivity spectra are analysed in terms of the dipole-allowed optical transitions at high symmetry $\mathrm{\ensuremath{\Gamma}}$, K, and ${\mathrm{K}}^{\ensuremath{'}}$ points, which further indicate that atomically thin ${\mathrm{Fe}}_{3}\mathrm{Ge}{\mathrm{Te}}_{2}$ films with odd layer-number might exhibit anomalous ferrovalley Hall effect. All these interesting findings thus suggest that 2D and bulk ferromagnetic ${\mathrm{Fe}}_{3}\mathrm{Ge}{\mathrm{Te}}_{2}$ are promising materials for high-density MO and spintronic nanodevices.

Intrinsic magnetism in two-dimensional Cr2X2Se (X = I, Br, Cl) monolayers

A novel family of two-dimensional Cr2X2Se (X = I, Br, Cl) monolayers with intrinsic magnetism has been predicted using first-principles calculations. The monolayer with the five atomic sublayers has two structures: structure I with ABCAB-type atomic sublayers and structure II with ABCBA-type atomic sublayers. It is found that the lowest energy states are ferromagnetic (FM) half metal for the structure I, and antiferromagnetic (AFM) semiconductor for the structure II, respectively. Phonon spectrum calculations and molecular dynamics simulations show that these lowest energy magnetic states are stable. Monte Carlo simulations based on the Ising model show that the Curie temperatures are about 94, 156 and 93 K for Cr2I2Se, Cr2Br2Se and Cr2Cl2Se monolayers in the structure I, respectively, which are above 77 K of the liquid-nitrogen transition temperature. The large magnetocrystalline anisotropy energies of about 1879, 68, 28 μeV per Cr atom for Cr2X2Se (X = I, Br, Cl) monolayers in the structure I show their importance in magnetic memory and storage. The magnetization direction is out of plane in Cr2I2Se and Cr2Br2Se, but is in plane in Cr2Cl2Se. Our study implies a new route in 2D electronics and spintronics.

Prediction of large magnetic anisotropy for non-rare-earth based permanent magnet of Fe16 − xMnxN2 alloys

Exploring the metastable magnetic nanostructures of Mn substituted α″-Fe16N2 with large saturation magnetization μ0MS, high Curie temperature TC and giant magnetic anisotropy are of technological merit as promising candidates for non-rare-earth based permanent magnets. Here, we present in-depth analysis for the structural and magnetic properties of Fe16 − xMnxN2 using first-principles calculations. We predict a large magnetocrystalline anisotropy energy (MAE) constant of K1 = 2.02 MJ/m3 for the Fe14Mn2N2 alloy, which is more than twice that of pristine Fe16N2. The underlying mechanism associated with boosting K1 is attributed to the local distortion of orbitals induced by Mn substitution. The MAE is also carefully analyzed in terms of reciprocal space analysis by employing the magnetic force theorem, revealing the regions in the Brillouin zone that are prominent for giving rise to MAE.

Magnetic and electronic properties of layered Sr2NiO2Cl2 with square planar coordination

Local coordination geometry is crucial in determining the physical properties of transition metal compounds. In this work, we report a detailed density functional theory study on the magnetic and electronic properties of layered Sr2NiO2Cl2, which possesses an unusual square planar coordination. Due to the crystal field and spin splitting, Ni 3d electrons fully occupy the dxz, dyz, and dxy orbitals, while partially occupy the dz2 and dx2-y2 states, leading to the high spin state of Ni2+ ions and strong antiferromagnetic in-plane nearest-neighbor exchange interaction J1. Thus, Sr2NiO2Cl2 is predicted to exhibit a G-type magnetic ground state, which all nearest-neighbor magnetic moments are antiparallel to each other in the NiO2 plane. A band gap is opened irrespective of the specific magnetic state since the unique square planar crystal field splitting. Finally, large orbital moments and giant easy-plane magnetocrystalline anisotropy energy are obtained, which is again related to the unique coordination environment.

First-principles study of magnetism and phase stabilities of V2 based antiferromagnetic Heusler alloys

We investigate the phase stability and magnetism of V2 based antiferromagnetic semiconductors by first-principles calculations. We first analyze the phase stability of the designed alloys by calculating the convex hull and find that keeping Al atoms in the Z sites is crucial to guarantee the stability against the segregation. The V2YAl (Y=V, Nb, and Ta) systems have relatively small hull distances and Néel temperatures higher than 1000 K are evaluated. The strong antiferromagnetic coupling between V atoms is rapidly decreasing with increasing the number of electrons due to the appearance of ferromagnetic double-exchange interaction. By applying a uniaxial strain to induce tetragonal distortion, a relatively large magneto-crystalline anisotropy energy is obtained for V2TaAl. It is claimed that V2YAl are thought to be good candidates for antiferromagnetic spintronics including gate-tunable magnetic properties.

Large easy-plane magnetic anisotropy in square planar coordinate Sr2CoO2X2 (X = Cl, Br)

Large magnetocrystalline anisotropy energy (MAE) is an important requirement for applications in spintronic devices. Here, we focus on layered cobalt oxyhalides Sr2CoO2X2 (X = Cl, Br) with unusual square planar coordination, which are naturally expected to possess a strong MAE. Based on density functional calculations, we find Co ions adopt a high spin state due to the large spin-exchange splitting and exhibit a sizable orbital moment of about 0.6 μB for both compounds. The in-plane nearest-neighbor exchange interaction J1 is antiferromagnetic coupling, and at least one order of magnitude stronger than other exchange interactions, which results in the observed G-type magnetic ground state. As expected, Sr2CoO2X2 have a giant MAE of about 13 meV per Co atom, and the magnetic moments prefer to lie in the ab plane, which is largely originated from the unique crystal field environment and could be explained by perturbation theory.

Structural, electronic and magnetic properties of the ordered binary FePt, MnPt, and CrPt3 alloys.

We perform ab initio simulations to investigate the structural, electronic and magnetic properties of the ordered binary FePt, MnPt, and CrPt3 alloys. In particular, equilibrium structural lattice parameters, electronic properties such as density of states (DOS), partial density of states (PDOS) and electronic band structure of each binary alloys are investigated and interpreted. Moreover, the magneto-crystalline anisotropy energies (MAE) are calculated. We found MAE values of FePt, MnPt and CrPt3 ordered alloys to be 2.66, 0.46 and 0.42 meV/f.u., respectively, corresponding to magneto-crystalline anisotropy constant K of 7.6 107, 1.3 107 and 1.1 × 107 erg/cm3, respectively. The large MAE and K values reveal that FePt, MnPt and CrPt3 binary alloys are eligible to be key components in magneto-optical and opto-electronic devices. In addition, we estimated the Curie temperatures of the three ordered alloys from exchange energy. We found the TC of L10-FePt, L10-MnPt and L12 CrPt3 to be 955 K, 989 K and 762 K, respectively. The high Curie temperatures obtained enable the ordered alloys to serve as write assist in Heat-Assisted Magnetic Recording (HAMR). We believe that our findings would pave the way to fabricate bulk and thin films based on the ordered binary FePt, MnPt, and CrPt3 ordered alloys that have attractive electronic and magnetic properties.

Designing rare-earth free permanent magnets in heusler alloys via interstitial doping

Based on high-throughput density functional theory calculations, we investigated the effects of light interstitial H, B, C, and N atoms on the magnetic properties of cubic Heusler alloys, with the aim to design new rare-earth free permanent magnets. It is observed that the interstitial atoms induce significant tetragonal distortions, leading to 32 candidates with large ( > 0.4 MJ/m3) uniaxial magneto-crystalline anisotropy energies (MAEs) and 10 cases with large in-plane MAEs. Detailed analysis following the perturbation theory and chemical bonding reveals the strong MAE originates from the local crystalline distortions and thus the changes of the chemical bonding around the interstitials. This provides a valuable way to tailor the MAEs to obtain competitive permanent magnets, filling the gap between high performance Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.

Two-dimensional magnetic semiconductors with room Curie temperatures

This paper shows that two-dimensional Ising-type ferromagnetic semiconductors TcSiTe3, TcGeSe3 and TcGeTe3 with high Curie temperatures around 200~500 K possess large magnetocrystalline anisotropy energy, large anomalous Hall conductivity, and large magneto-optical Kerr angles due to their large spin-orbit couplings.

Low-temperature MnBi alloys: Electronic and magnetic properties, constitution, morphology and fabrication (Review article)

The article reviews the rich phenomena of physical properties of MnBi. The diverse phenomena include strong spin-orbit interaction, anomalous temperature dependence of the coercivity and the magneto-crystalline anisotropy field, unique magneto-optical properties. Issues addressed include the nature of the electronic ground states of MnBi, the electronic and magnetic structures, Fermi surface, magneto-crystalline anisotropy, x-ray magnetic dichroism. The discussion includes key experiments, such as optical and magneto-optical spectroscopic measurements, de Haas-van Alphen (dHvA) measurements, x-ray photoemission and x-ray absorption spectroscopy measurements as well as x-ray magnetic circular dichroism. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U were found to be crucial for the Fermi surface, cyclotron masses, magneto-optical properties, and x-ray magnetic circular dichroism. The microscopic origin of unique magneto-crystalline anisotropy and giant Kerr effect in MnBi is analyzed in detail. The huge Kerr effect in MnBi is caused by the combination of a sizable magnetic moment on manganese, the large spin-orbit coupling of bismuth, and a strong hybridization between the manganese 3d and the bismuth 6p states. The magneto-optically active states are mainly the 6p states of Bi. We show that the observed temperature dependence of the magneto-crystalline anisotropy can be explained taking into account the spin-orbit interaction together with strong Coulomb electron-electron interaction. The SO coupling of Bi is equally responsible for the large magneto-crystalline anisotropy energy as is the exchange splitting of Mn. The fabrication, morphology, and constitution of low-temperature MnBi alloys in bulk, thin films, and nanoparticles are discussed. The nanocomposite permanent magnetic materials based on MnBi, (Co, Fe) and Nd2Fe14B are also discussed.

Prediction of room-temperature half-metallicity in layered halide double perovskites

Half-metallic ferromagnets (HMFs) that possess intriguing physical properties with completely spin-polarized current are key candidates for high-efficiency spintronic devices. However, HMFs that could simultaneously have high Curie temperature (Tc), wide half-metallic gap (ΔHM), and large bulk magnetocrystalline anisotropy energy (MAE) are very rare, which significantly restrict their room-temperature (RT) applications. In this article, through materials screening in layered halide double perovskites (LHDPs), we have theoretically identified that Cs4FePb2Cl12, which has good crystallographic, dynamic and thermal stabilities, possesses an intrinsic half-metallic ground-state with a high Tc ~ 450 K. Interestingly, the long-range ferromagnetic ordering in bulk Cs4FePb2Cl12 is contributed by the strong super-superexchange interactions between the neighboring Fe d orbitals mediated by different anionic Cl p orbitals. The high Tc of layered Cs4FePb2Cl12 can be well maintained even in the monolayer limitation, i.e., Tc ~ 370 K for Cs4FePb2Cl12 monolayer, which is critical for nanoscale device applications. Moreover, both bulk and monolayer Cs4FePb2Cl12 can exhibit wide ΔHM ~ 0.55 eV and large MAE >320 μeV/Fe, comparable to that of the best HMFs reported in the literature. Our findings can significantly extend the potentials of LHDPs for high-temperature spintronic applications.

Influence of changes in electronic structure on magnetocrystalline anisotropy of YCo5 and related compounds

Abstract Density functional theory calculations have been carried out for the hard magnetic compound Y C o 5 and its related phases. The calculations provide a straightforward but accurate method, as reflected in good agreement obtained with experimental results in terms of saturation magnetization and magnetocrystalline anisotropy energy (MAE). For the calculations we used the projector augmented wave method with GGA-PBE approximation and included spin-orbit coupling and ( U , J ) potentials, which are calculated to convergence. It is shown that these properties are influenced by the crystal structure and atomic distances, hence the crystal structures have been optimized and relaxed. The influence of changes in symmetry, distances and lattice parameters are studied, as well as the effect of substituting one C o - atom by F e or C u as examples for a magnetic and a non-magnetic impurity. The comparison between Y C o 5 and hcp - C o shows the importance of atomic environments and lattice symmetry for a large MAE. The calculations predict that F e and C u both reduce MAE, but F e increases magnetization. Despite lacking 4 f - orbitals as compared to S m C o 5 , Y C o 5 exhibits a large anisotropy, originating from the contribution of the C o - atoms. We have also shortly studied the influence of 4 f - electrons for rare earths R = P r and S m on MAE for comparison. Y C o 4 F e , Y C o 4 C u , S m C o 4 F e and S m C o 4 C u are calculated to have MAE values of 2.1 M J / m 3 , 2.7 M J / m 3 , 19.2 M J / m 3 and 8 . 2 M J / m 3 at 0 K respectively.

Structural and magnetic properties of Pr5Si3-xGex compounds

The crystal structures, magnetic properties and electronic structures of pseudo-binary compounds Pr5SixGe3-x were investigated. With the increase of the Ge content, structure of Pr5SixGe3-x gradually changes from the tetragonal Cr5B3-type to the hexagonal Mn5Si3-type. For the compounds with the tetragonal structure, the unit cell volumes as well as the magneto-crystalline anisotropy energy (MAE) increase with the Ge content, leading to the diminishing of the magnetization and the maximum magnetic entropy changes -ΔSM. As compared to the binary compound Pr5Si3, the intermetallic compounds with Ge doping show broader working temperature span and considerably large relative cooling power (213.9, and 184.8 J kg−1 at ΔH = 50 kOe for Pr5Si2.5Ge0.5 and Pr5Si2Ge, respectively). For the hexagonal compound Pr5Ge3, a large MAE and an easy magnetization direction close to c axis (polar angle θ ∼7°) were calculated, which is related to the macroscopic magnetic transition behavior at low temperature.

Designing Rare-Earth Free Permanent Magnets in Heusler Alloys Via Interstitial Doping

Based on high-throughput density functional theory calculations, we investigated the effects of light interstitial H, B, C, and N atoms on the magnetic properties of cubic Heusler alloys, with the aim to design new rare earth free permanent magnets. It is observed that the interstitial atoms induce significant tetragonal distortions, leading to 32 candidates with large (> 0.4 MJ/m3) uniaxial magneto-crystalline anisotropy energies (MAEs) and 10 cases with large in-plane MAEs. Detailed analysis following the the perturbation theory and chemical bonding reveals the strong MAE originates from the local crystalline distortions and thus the changes of the chemical bonding around the interstitials. This provides a valuable way to tailor the MAEs to obtain competitive permanent magnets, filling the gap between high performance Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.