Half-metallic Antiferromagnets Research Articles

Half-metallic antiferromagnets induced by non-magnetic adatoms on bilayer silicene.

Transition metal-free magnetism and two-dimensional p-state half-metals have been a fascinating subject of research due to their potential applications in nanoelectronics and spintronics. By applying density functional theory calculations, we predict that bilayer silicene can be an interlayer antiferromagnetic ground state. Interestingly, the half-metallicity is realized by adsorbing non-magnetic atoms on the antiferromagnetic bilayer silicene in the absence of transition magnetic atoms, nanoribbons, ferromagnetic substrates and magnetic field. Then, on the basis of first principles calculations and theoretical analysis, we show that the realization of half-metallicity is induced by the split of antiferromagnetic degeneracy due to the localization of transfer charge from the adatom to silicene. Our findings may open a new avenue to silicene-based electronic and spintronic devices.

Realization of half-metal antiferromagnetic (HM-AFM) behaviour in double perovskite Sr2CrReO6 on substitution of Tc at Cr site: Promising material for optoelectronics and thermoelectric applications via DFT framework

• We have studied Sr 2 AReO 6 (A=Cr, Tc) by using both PBEsol-GGA and PBEsol+U. • We report ferrimagnetic half-metal in Sr 2 CrReO 6 while Sr 2 TcReO 6 shows antiferromagnetic half-metal (AFM-HM) behavior. • Among the two materials Sr 2 TcReO 6 is a promising material for spintronic application due to low loss of energy. • Also double perovskite Sr 2 TcReO 6 (STRO) shows high absorption coefficient at UV-Vis range of photon energy. Using the application of the first principle within the Full Potential Linearized Augmented Plane wave (FP-LAPW) method, the electronic, magnetic, optical and thermoelectric properties of double perovskite oxides Sr 2 AReO 6 (A=Cr, Tc)were systematically investigated. We have used the most appropriate functionals like PBEsol-GGA and PBEsol+U. The replacement of Cr atom by Tc atom in Sr 2 CrReO 6 leads to the transition of the magnetic configuration from ferrimagnet to complete antiferromagnet half-metal (AFM-HM) with zero magnetic moments. The mechanisms that govern the ferrimagnetism/antiferromagnetism in the two double perovskites are the Zener double exchange and hybridization p-d, respectively. A careful analysis of the optical and thermoelectric properties in this study leads to the conclusion that the antiferromagnet double perovskite Sr 2 TcReO 6 (STRO)has the power to convert the maximum amount of sunlight in the visible range compared to the ferromagnet compound Sr 2 CrReO 6 (SCRO). Further, we have obtained an optimal figure of merit (ZT∼1) and high electrical conductivity. Finally, the half-metallic antiferromagnetic double perovskiteSTRO is a potential energy material for the spintronic device, photovoltaic solar cells and thermoelectric applications.

Electronic Structure and Magnetic Properties of OsCrMnSb and IrCrMnSb from Ab Initio Calculations

The structural, elastic, electronic and magnetic properties of quaternary OsCrMnSb and IrCrMnSb Heusler alloys are performed employing ab initio electronic structure calculations. It has been identified that the YI type is the most stable structure among the three configurations for both OsCrMnSb and IrCrMnSb alloys in the magnetic state. The calculated cubic elastic constants show that these alloys fulfill the mechanical stability criteria. The band structures and density of state calculations reveal the half-metallic (HM) behavior of these alloys with a direct gap, and the half-metallicity is rather originated from the Cr-d states. Results on magnetic properties suggest that OsCrMnSb and IrCrMnSb are HM antiferromagnets. However, the inclusion of spin–orbit coupling affects strongly the IrCrMnSb alloy, losing its HM nature.

Strongly Correlated Molecular Magnet with Curie Temperature above 60 K

Summary Two-dimensional crystals with ferromagnetic ordering would lead to unprecedented possibilities for magnetic, magneto-optic, and magnetoelectric applications. However, long-range ferromagnetic ordering in two-dimensional van der Waals materials is strongly diminished by thermal fluctuation, while three-dimensional systems show the stiffness of magnetic ordering temperature to magnetic fields. Here, we report the discovery of intrinsic ferromagnetic ordering temperature of 60 K in an iron/tetracyanoquinodimethane layer via superconducting precursor. In such a molecular ferromagnet, an unprecedented control of ferromagnetic fluctuation temperature by ∼200% improvement is realized through magnetic fields. We demonstrate magnetodielectric coupling with a concomitant transition in magnetic ordering. A small magnetic field of 0.01 T enables an effective route to realize a sizable transition shift in magnetodielectric states. Stimulated by photoirradiation, it manifests a hidden metallic conducting state, declaring a metallic ferromagnet. The molecular ferromagnet and photoirradiation-induced hidden metallic phase present a “holy grail” in the field of molecular conducting magnets.

Promising spintronics: Mn-based Heusler alloys Mn3Ga, Mn2YGa (Y = V, Nb, Ta), ScMnVGa

High spin-polarized materials are expected for the development of spintronic devices. In this work, we are aiming to find new spintronic materials in Mn-based binary, ternary and quaternary Heusler alloys by using the first-principles calculations. We investigated structures, electronic properties, magnetic, tetragonal distortion and mechanic properties of Mn3Ga, Mn2YGa (Y = V, Nb, Ta) and ScMnVGa. The results show that Mn3Ga, ScMnVGa type-I, and type-II have lower energy in antiferromagnetic (AFM) states than ferromagnetic (FM) and paramagnetic (NM). Mn2YGa (Y = V, Nb, Ta) compounds are more stable in FM states. The results of electronic and magnetic properties indicate that Mn3Ga is a gapless half-metallic antiferromagnet (Gapless HM-AFM). Mn2VGa and Mn2NbGa belong to gapless half-metallic ferrimagnets (Gapless HM-FE). Mn2TaGa is ferrimagnets. ScMnVGa type-I is half-metallic antiferromagnets (HM-AFM) and type-II belongs to spin gapless semiconductors with AFM (SGSs-AFM). Inspired by Ferromagnetic shape memory alloys (FAMAs), we performed tetragonal deformation of those compounds, and we predicted that Mn3Ga, Mn2YGa (Y = V, Nb, Ta) have possible martensitic transformations. Finally, the mechanical stability and elastic properties of above-mentioned in both cubic and tetragonal structures were discussed in detail.

Magnetic and Structural Properties of Exchange Coupled Heusler Alloy NiO/Co2FeAl Interfaces with n-and p-Type Silicon Substrates

Exchange coupled structures of half metallic ferromagnets, Heusler Alloy (FM), Co2FeAl (CFA) and antiferromagnet (AF), NiO were fabricated by electron beam evaporation technique on n- and p-type Si substrates. These fabricated bilayer structures were further characterized for structural, morphological and magnetic point of views using x-ray diffraction (XRD), atomic/magnetic force microscopy (AFM/MFM) and vibrating sample magnetometer (VSM) techniques. Structural study shows the presence of CFA alloy and NiO phase. Surface morphology shows the granular feature of the top surface with grain size of 200–300 nm due to clustering of smaller grains. Smaller sized magnetic domains have been observed for the structures. Hysteresis behaviour of NiO/CFA/Si structures shows the ferromagnetic behaviour for in-plane orientation with negligible exchange bias whereas a significant exchange bias for out of plane orientation has been observed. The observed result could be understood due to surface roughness and arrangements of spins near the interface of ferromagnetic and anti-ferromagnetic layers.

Evolution of electronic and magnetic properties in a series of iridate double perovskites Pr2−xSrxMgIrO6 (x=0,0.5,1.0)

Spin-orbit coupling (SOC) plays a crucial role in magnetic and electronic properties of 5$d$ iridates. In this paper we have experimentally investigated the structural and physical properties of a series of Ir-based double perovskite compounds Pr$_{2-x}$Sr$_x$MgIrO$_6$ ($x$ = 0, 0.5, 1; hereafter abbreviated as PMIO, PSMIO1505, and PSMIO). Interestingly, these compounds have recently been proposed to undergo a transition from the spin-orbit-coupled Mott insulating phase at $x$ = 0 to the elusive half-metallic antiferromagnetic (HMAFM) state with Sr doping at $x$ = 1. However, our detailed magnetic and electrical measurements refute any kind of HMAFM possibility in either of the doped samples. In addition, we establish that within these Pr$_{2-x}$Sr$_x$MgIrO$_6$ double perovskites, changes in Ir-oxidation states (4+ for PMIO to 5+ for PSMIO via mixed 4+/5+ for PSMIO1505) lead to markedly different magnetic behaviors. While SOC on Ir is at the root of the observed insulating behaviors for all three samples, the correlated magnetic properties of these three compounds develop entirely due to the contribution from local Ir moments. Additionally, the magnetic Pr$^{3+}$ (4$f^2$) ions, instead of showing any kind of ordering, only contribute to the total paramagnetic moment. It is seen that the PrSrMgIrO$_6$ sample does not order down to 2 K despite antiferromagnetic interactions. But, the $d^5$ iridate Pr$_2$MgIrO$_6$ shows a sharp antiferromagnetic (AFM) transition at around 14 K, and in the mixed valent Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ sample the AFM transition is shifted to a much lower temperature ($\sim$ 6 K) due to weakening of the AFM exchange.

Electrically induced 2D half-metallic antiferromagnets and spin field effect transistors

Engineering the electronic band structure of material systems enables the unprecedented exploration of new physical properties that are absent in natural or as-synthetic materials. Half metallicity, an intriguing physical property arising from the metallic nature of electrons with singular spin polarization and insulating for oppositely polarized electrons, holds a great potential for a 100% spin-polarized current for high-efficiency spintronics. Conventionally synthesized thin films hardly sustain half metallicity inherited from their 3D counterparts. A fundamental challenge, in systems of reduced dimensions, is the almost inevitable spin-mixed edge or surface states in proximity to the Fermi level. Here, we predict electric field-induced half metallicity in bilayer A-type antiferromagnetic van der Waals crystals (i.e., intralayer ferromagnetism and interlayer antiferromagnetism), by employing density functional theory calculations on vanadium diselenide. Electric fields lift energy levels of the constituent layers in opposite directions, leading to the gradual closure of the gap of singular spin-polarized states and the opening of the gap of the others. We show that a vertical electrical field is a generic and effective way to achieve half metallicity in A-type antiferromagnetic bilayers and realize the spin field effect transistor. The electric field-induced half metallicity represents an appealing route to realize 2D half metals and opens opportunities for nanoscale highly efficient antiferromagnetic spintronics for information processing and storage.

Development of half metallicity within mixed magnetic phase of Cu1−xCoxMnSb alloy

Cubic half-Heusler Cu1−xCoxMnSb () compounds have been investigated both experimentally and theoretically for their magnetic, transport and electronic properties in search of possible half metallic antiferromagnetism. The systems (Cu,Co)MnSb are of particular interest as the end member alloys CuMnSb and CoMnSb are semi metallic (SM) antiferromagnetic (AFM) and half metallic (HM) ferromagnetic (FM), respectively. Clearly, Co-doping at the Cu-site of CuMnSb introduces changes in the carrier concentration at the Fermi level that may lead to half metallic ground state but there remains a persistent controversy whether the AFM to FM transition occurs simultaneously. Our experimental results reveal that the AFM to FM magnetic transition occurs through a percolation mechanism where Co-substitution gradually suppresses the AFM phase and forces FM polarization around every dopant cobalt. As a result a mixed magnetic phase is realized within this composition range while a nearly HM band structure is developed already at the 10% Co-doping. Absence of T2 dependence in the resistivity variation at low T-region serves as an indirect proof of opening up an energy gap at the Fermi surface in one of the spin channels. This is further corroborated by the ab initio electronic structure calculations that suggests that a nearly ferromagnetic half-metallic ground state is stabilized by Sb-p holes produced upon Co doping.

Two-Dimensional Metal–Organic Half-metallic Antiferromagnet: CoFePz

Half-metals are always accompanied by ferromagnetism with undesired stray magnetic field which may be harmful in highly integrated circuits. By contrast, half-metallic antiferromagnets (HMAFMs) can achieve fully spin-polarized current without stray magnetic field, enabling spintronic filed sensing and magnetic memories. Using first-principles calculations, we demonstrated that the tantalizing HMAFM can be realized in a two-dimensional (2D) metal–organic framework (MOF) containing Co ions and octa-amino-substituted iron-porphyrazines (CoFePz). The strong p–d exchange interaction between ions and ligands leads to an antiferromagnetic ground state with metallic features in one spin direction and semiconducting features in the opposite spin direction. Monte Carlo simulations based on the Ising model on an edge-centered square lattice indicate that the Neel temperature of the CoFePz (247 K) is much higher than the temperature of liquid nitrogen. Considering the huge number of MOFs, it is expected that the pres...

Cationic order versus La-O covalency in LaA (Ca,Ba) VMoO6 double perovskites

We have investigated the structural and physical properties of double perovskite (DP) $\mathrm{La}A{\mathrm{VMoO}}_{6}$ ($A={\mathrm{Ca}}^{2+}$, ${\mathrm{Ba}}^{2+}$; abbreviated as LCVMO and LBVMO from now on) compounds, proposed to be possible half-metallic antiferromagnets (HMAFMs). Here we show that within $\mathrm{La}A{\mathrm{VMoO}}_{6}$ double perovskite structure, La-O covalency competes against $B$-site as well $A$-site cationic order and this competition critically influences their physical properties. Evidently, the presence of ${\mathrm{Ca}}^{2+}$ or ${\mathrm{Ba}}^{2+}$ at the $A$ site along with ${\mathrm{La}}^{3+}$ would offer a tool to modify the $A$-site ordering and consequently influence the La-O covalency as well. Our experimental results reveal that LCVMO lies at the extreme end of this family and accommodates large scale phase separation in terms of La, V, and Ca, Mo-rich phases as a result of dominant La-O covalency. On the other hand, LBVMO is more correctly described as a layered $A$-site ordered and nearly complete $B$-site disordered double perovskite where cationic order dominates the La-O covalency. The general trend of our experimental findings is in agreement with the ab initio electronic structure calculations, carried out on realistic structures based on local coordination obtained from extended x-ray-absorption fine-structure study.

반쪽 금속 호이슬러 화합물 Mn3Ga의 연 X선 방사광 분광 연구

이 연구에서는 방사광을 이용한 연 X-선 흡수 분광법(soft X-ray absorption spectroscopy: XAS)과 광전자 분광법(photoemission spectroscopy: PES) 을 이용하여 반쪽금속 반강자성체 후보 물질인 <TEX>$Mn_3Ga$</TEX> 호이슬러 화합물의 전자구조를 연구하였다. 이 연구에 사용된 시료는 full-Heusler <TEX>$Mn_3Ga$</TEX>로 ball milling 후 열처리하지 않은 시료와 ball milling 후 <TEX>$400^{\circ}C$</TEX>에서 열처리한 두 시료를 사용하였다. XAS 분석에 의하면 <TEX>$Mn_3Ga$</TEX>에서 Mn 이온들의 원자가는 <TEX>$Mn^{2+}$</TEX> 상태임을 알 수 있었으며, 국소적으로 팔면체 대칭성을 가진 Mn 이온들과 사면체 대칭성을 가진 Mn 이온들이 섞여 있음을 알 수 있었다. 그리고 <TEX>$Mn_3Ga$</TEX>의 가전자띠 PES 스펙트럼은 전자구조 계산에 의한 반쪽 금속성 상태밀도와 대체로 유사함을 발견하였다. By employing photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS), the electronic structure of the candidate half-metallic antiferromagnet of <TEX>$Mn_3Ga$</TEX> Heusler compound has been investigated. We have studied two ball-milled <TEX>$Mn_3Ga$</TEX> powder samples, one after annealing and the other without annealing, respectively. Based on the Mn 2p XAS study, we have found that Mn ions are nearly divalent in <TEX>$Mn_3Ga$</TEX> and that the Mn ions having the locally octahedral symmetry and those having the locally tetrahedral symmetry are both present in <TEX>$Mn_3Ga$</TEX>. We have found relatively good agreement between the measured valence-band PES spectrum of <TEX>$Mn_3Ga$</TEX> and the calculated density of states, which is in agreement with the half-metallic electronic structure of <TEX>$Mn_3Ga$</TEX>.

Compensated half metallicity in osmium double perovskite driven by doping effects

Using the first-principles density functional approach, we investigate Ca2FeOsO6, a material of double perovskite structure synthesized recently. According to the calculations, Ca2FeOsO6 is a ferrimagnetic Mott-insulator with the total magnetic moment per unit cell. The system is found to be influenced by the cooperative effect of spin–orbit coupling (SOC) and Coulomb interactions of Fe-3d and Os-5d electrons, in addition to the crystal field. When Fe is replaced with Ni, the system exhibits half metallic (HM) states desirable for spintronic applications. In [Ca2Fe1−xNixOsO6]2, HM ferrimagnetism is observed with per unit cell for doping rate x = 0.5, whereas HM antiferromagnetism (HMAFM) with nearly zero spin magnetization in the unit cell is achieved for x = 1 respectively. It is emphasized that half metallicity is retained in presence of SOC due to the large exchange-splitting between spin-up and spin-down bands close to the Fermi level.

Possible half-metallic antiferromagnetism in an iridium double-perovskite material

Using the first-principles density functional approach, we investigate a material Pr$_2$MgIrO$_6$ (PMIO) of double perovskite structure synthesized recently. According to the calculations, PMIO is a magnetic Mott-Hubbard insulator influenced by the cooperative effect of spin-orbit coupling (SOC) and Coulomb interactions of Ir-5$d$ and Pr-4$f$ electrons, as well as the crystal field. When Pr is replaced with Sr gradually, the system exhibits half metallic (HM) states desirable for spintronics applications. In [Pr$_{2-x}$Sr$_x$MgIrO$_6$]$_2$, HM antiferromagnetism (HMAFM) with zero spin magnetization in the unit cell is obtained for $x=1$, whereas for $x=0.5$ and 1.5 HM ferrimagnetism (HMFiM) is observed with $\mu_{\rm tot}=3\mu_{\rm B}$ and $\mu_{\rm tot}=-3\mu_{\rm B}$ per unit cell respectively. It is emphasized that the large exchange splitting between spin-up and spin-down bands at the Fermi level makes the half metallicity possible even with strong SOC.

Cation ordering induced semiconductor to half metal transition in La2NiCrO6

La2NiCrO6, previously proposed to be a candidate of half metallic antiferromagnetism, is revisited using the first-principles calculation.

Half metallic antiferromagnetic behavior in doped TiO2 rutile with double impurities (Os, Mo) from ab initio calculations

Electronic and magnetic calculations were based on density functional theory within the generalized gradient approximation for II–VI compound semiconductor TiO2 doped with single impurity Os and Mo; these compounds are half-metallic ferromagnets in their ground state with a total magnetic moment of 2μB for both systems. Then, doping TiO2 with double impurities (Os, Mo) was performed. As a result, Ti1−2xOsxMoxO2 with x=0.065 is a half-metallic antiferromagnet with 100% spin polarization of the conduction electrons crossing the Fermi level, without showing a net magnetization. Moreover, the Ti14OsMoO32 compound is stable energetically than Ti1−xMoxO2 and Ti1−xOsxO2. The antiferromagnetic interaction in the Ti1−2xOsxMoxO2 system is attributed to the double exchange mechanism, and the latter could also be the origin of their half-metallic behavior.

Study of atomic and molecular oxygen chemisorption on BC3 nanotubes with Stone–Wales defects using density functional theory

Density functional theory calculations are used to study the adsorption of chemical species including oxygen atom and oxygen molecule on the perfect and defective BC3 nanotubes. Stone–Wales topological defects with four different bond rotations have been examined. The adsorption of atomic oxygen is exothermic in all cases, while for the molecular oxygen, some sites showed endothermic adsorption. Comparative studies on the adsorption of these chemical species shows the maintenance of semiconductive behavior of nanotubes, except for one of the systems, the defected nanotube with a circumferential C–C bond rotation. In this system, the adsorption of molecular oxygen generates a half-metallic antiferromagnet. The results obtained in this paper are relevant for chemical sensing and spintronics applications.

Obtaining half-metallic ferrimagnetism and antiferromagnetism by doping Mn and Fe for DO3-type Heusler compound Cr3Si

The electronic structure, magnetic properties and occupation feature of DO3-type Heusler compounds (Cr1−xMnx)3Si and (Cr1−xFex)3Si (x=n/12, n=0, 2, 4, 6, 8, 10, 12) have been investigated by first principles calculations. The compounds Cr3Si, (Cr1–4/12Mn4/12)3Si, Mn3Si, (Cr1–2/12Fe2/12)3Si, and (Cr1–6/12Fe6/12)3Si are predicted to be half-metallic ferrimagnets. The compound (Cr1–4/12Fe4/12)3Si is predicted to be half-metallic antiferromagnet, which is applicable to spintronic devices due to its zero magnetization. The Fe atoms of (Cr1−xFex)3Si prefer to occupy the (A,C) sites while the Mn atoms of (Cr1−xMnx)3Si tend to occupy the B site, indicating that the occupation of doping atoms is affected strongly by the inter-atom hybridization and the 3d electrons number of doping atoms is not a determining factor. In addition, the results confirm the uniformity rule that the A site is equivalent to C site and the doping atoms prefer to enter the two sublattice uniformly. The more symmetric surroundings of atom coordination in B site in contrast to (A,C) site leads to a typical 3d electronic splitting peaks. The total moment for all the doped compounds (Cr1−xMnx)3Si and (Cr1−xFex)3Si agrees well with the Slater–Pauling rule. The coexisting Cr(B) and Cr(A,C) atoms show antiferromagnetic coupling character for both (Cr1−xMnx)3Si and (Cr1−xFex)3Si. The coexisting doping Mn(B) and Mn(A,C) atoms show antiferromagnetic coupling character for (Cr1−xMnx)3Si while Fe(B) and Fe(A,C) atoms show ferromagnetic coupling character for (Cr1−xFex)3Si.

Antiferromagnetic half-metals, gapless half-metals, and spin gapless semiconductors: The D03-type Heusler alloys

High-spin-polarization materials are desired for the realization of high-performance spintronic devices. We combine recent experimental and theoretical findings to theoretically design several high-spin-polarization materials in binary D03-type Heusler alloys: gapless (zero-gap) half-metallic ferrimagnets of V3Si and V3Ge, half-metallic antiferromagnets of Mn3Al and Mn3Ga, half-metallic ferrimagnets of Mn3Si and Mn3Ge, and a spin gapless semiconductor of Cr3Al. The high spin polarization, zero net magnetic moment, zero energy gap, and slight disorder compared to the ternary and quaternary Heusler alloys make these binary materials promising candidates for spintronic applications. All results are obtained by the electronic structure calculations from first-principles.

Half-metallic antiferromagnetic behavior of double perovskite Sr2OsMoO6: First principle calculations

Electronic structure calculations based on density functional theory within the generalized gradient approximation for double perovskite Sr2FeMoO6 and Sr2OsMoO6 have been performed using the accurate full potential augmented spherical wave method. By substituting Fe atoms by Os in the double perovskite structure oxides we have shown that it is possible to realize half-metallic antiferromagnets with 100% spin polarization of the conduction electrons crossing the Fermi level, without showing a net magnetization. To support our results, GGA+U electronic structure calculations have been performed showing that the half-metallic antiferromagnetic state still persists. We conclude that the origin of the antiferromagnetism in Sr2OsMoO6 may be attributed to both superexchange and generalized double exchange mechanisms via the B(3d,5d)–O(2p)–B′(4d) coupling.