Half-metallic Antiferromagnets Research Articles

Physical properties of double perovskite compounds ALaVMoO 6 (A=Ca, Sr, Ba)—a possible half-metallic antiferromagnetic system

Double perovskite compounds ALaVMoO 6 (A=Ca, Sr, Ba) have been synthesized and their electrical and magnetic properties have been investigated. Magnetization measurements have indicated the possible antiferromagnetic transitions at 120 and 130 K for A=Ca and Sr samples, respectively. Electrical resistivity ρ for this system shows metallic temperature dependence from 300 to 20 K, though the sample with A=Ca shows weak semiconducting behavior in the low temperature region (<70 K). Considering the magnetic and electrical properties and assuming the V 3+ S=1 and Mo 4+ S=1 valence and spin states, the samples with A=Ca and Sr can be promising candidates for half-metallic antiferromagnets.

Computational design of multifunctional materials

We propose a general scheme for the computational design of new materials using density functional theory. We then apply the scheme to two classes of materials; ferromagnetic ferroelectrics and half-metallic antiferromagnets. Our first “designer” ferromagnetic ferroelectric has subsequently been synthesized and the predicted properties verified. Our computations on half-metallic antiferromagnets have stimulated experimental study but the phenomenon remains unconfirmed.

Vacancy-induced half-metallicity in MnO and NiO

We report on vacancy induced half-metallicity in the prototype Mott-insulating substances MnO and NiO. By embedding a cation vacancy into a magnetic system a new road opens up to the construction of half-metallic antiferromagnets. For ${\mathrm{Ni}}_{0.97}\mathrm{O}$ we find a half-metallic antiferromagnet, a system hitherto only proposed for complicated crystal structures.

Realization of La 2MnVO 6: search for half-metallic antiferromagnetism?

Single-phase polycrystalline La 2MnVO 6 samples were synthesized by arc-melting and characterized by X-ray diffraction, magnetization and resistivity measurements. We find that the compound has cubic (space group Fm3̄ m), partly ordered double perovskite structure. The sample exhibits ferrimagnetic behavior and variable-range hopping conductivity. We conclude based on the magnetic properties that both Mn and V ions are trivalent; moreover, the Mn 3+ ions are in a high spin state, which is the reason that the compound is not a half-metallic antiferromagnet.

Half-metallic antiferromagnetic double perovskites:LaAVRuO6(A=Ca,Sr, and Ba)

Based on the theoretical exploration of electronic structures, we propose that the ordered double perovskites LaAVRuO$_6$ and LaVO$_3$/ARuO$_3$ (001) superlattice (A = Ca, Sr and Ba) are strong candidates for half-metallic (HM) antiferromagnets (AFMs). %LaAVRuO$_6$ and LaVO$_3$/ARuO$_3$ have the %100% spin polarizations at the Fermi level but with zero %total magnetic moments. We have shown that the HM-AFM nature in LaAVRuO$_6$ is very robust regardless of (i) divalent ion replacement at A-sites, (ii) oxygen site relaxation, (iii) the inclusion of the Coulomb correlation, and (iv) cation disorder. A type of the double exchange interaction is expected to be responsible for the half-metallicity and the antiferromagnetism in these systems.

Half-Metallic Electronic Structures of Thiospinels

We have investigated electronic and magnetic properties of the thiospinel systems of A B 2 S 4 type ( A , B : transition metals), using the linearized muffin-tin orbitals (LMTO) bands method both in the local-spin-density approximation (LSDA) and the LSDA incorporating the Coulomb correlation interaction U (LSDA+ U ) scheme. The orbital ordering in FeCr 2 S 4 and the half-metallic property in its metallic phase are demonstrated based on the LSDA+ U electronic structures. The orbital magnetic moment is obtained by taking into account the spin–orbit interaction. We have also explored the possibility of fabricating half-metallic antiferromagnets (HM-AFMs) in thiospinel systems, which are non-magnetic metals but their conduction electrons are 100% spin-polarized.

Half-metallic antiferromagnets in thiospinels

We have theoretically designed the half-metallic (HM) antiferromagnets (AFMs) in thiospinel systems, $\rm Mn(CrV)S_{4}$ and $\rm Fe_{0.5}Cu_{0.5}(V_{0.5}Ti_{1.5})S_{4}$, based on the electronic structure studies in the local-spin-density approximation (LSDA). We have also explored electronic and magnetic properties of parent spinel compounds of the above systems; $\rm CuV_{2}S_{4}$ and $\rm CuTi_{2}S_{4}$ are found to be HM ferromagnets in their cubic spinel structures, while $\rm MnCr_{2}S_{4}$ is a ferrimagnetic insulator. We have discussed the feasibility of material synthesis of HM-AFM thiospinel systems.

The Josephson effect in single spin superconductors

The Josephson effect provides a primary signature of single spin superconductivity (SSS), the as yet unobserved superconducting state which was proposed recently as a low temperature phase of half-metallic anti ferro magnets. These materials are insulating in the spin-down channel, but are metallic in the spin-up channel. The SSS state is characterized by a unique form of p-wave pairing within a single spin channel. We develop the theory of a rich variety of Josephson effects that arise due to the form of the SSS order parameter. Tunneling is allowed at a SSS–SSS′ junction, but of course depends on the relative orientation of their order parameters. No current flows between an SSS and an s-wave BCS system as a result of their orthogonal symmetries, which potentially can be used to distinguish SSS from other superconducting states. Single spin superconductors also offer a means to probe other materials, where tunneling is a litmus test for any form of “triplet” order parameter.

Spin-density-functional-based search for half-metallic antiferromagnets

We present results based on local spin density calculations of a computational search for half-metallic (HM) antiferromagnetic (AFM) materials within the class of double perovskite structure oxides LaM'M''O3 that incorporate open shell 3d (or 4d) transition metal ions M', M''. The pairs M'M'' = MnCo, CrFe, CrRu, CrNi, MnV, and VCu are studied. La2VMnO6 is the most promising candidate, with the HM AFM phase more stable by 0.17 eV/cell than the ferromagnetic phase. La2VCuO6 is another promising possibility, but due to S=1/2 ions quantum fluctuations my play an important role in determining the ground state magnetic and electronic structure. This study indicates that HM AFM materials should not be prohibitively difficult to find.

Antiferromagnetism in a Heusler Alloy Fe2VSi

Antiferromagnetism has been found in a Heusler alloy Fe2VSi from measurements of electrical resistivity, magnetic susceptibility and Mössbauer spectroscopy of 57Fe. The Néel and Weiss temperatures are 123 K and -212 K, respectively. The magnetic moment of an Fe atom estimated from Mössbauer spectrum splitting is 0.22 µ B at 15 K. The effective moment determined from Curie-Weiss susceptibility above 123 K is 1.87 µ B . The results are discussed in relation to a half-metallic antiferromagnet.

Half-metallic antiferromagnets.

This Letter discusses the possibility of realizing half-metallic antiferromagnets, i.e., systems with 100% spin polarization of the conduction electrons without showing a net magnetization. The predictions are based on electronic structure calculations using the local density approximation.

Half-metallic magnetism in the 1990s

The possibility of designing half-metallic magnetic multilayer systems is investigated. In part two the prospects of realizing a half-metallic antiferromagnet with emphasis on applications in scanning-tunneling microscopy is discussed.

Recent developments in half-metallic magnetism

The compound PtMnSb is a half-metallic ferromagnet and its unusual band structure is intimately connected with the high Magneto Optical Kerr Effect (MOKE). In this paper it will be discussed how various types of substitutions can modify this band structure and lead to possible enhancement of the MOKE transitions. Novel half-metallic systems will be presented comprising half-metallic ferrimagnets and half-metallic antiferromagnets.