Spin-Peierls state versus Néel state in doped CuGeO3.

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Half-metallic antiferromagnets are the ideal materials for spintronic applications since their zero magnetization leads to lower stray fields and thus tiny energy losses. Starting from the Mn2VAl and Mn2VSi alloys we substitute Co and Fe for Mn and we show by means of first-principle electronic structure calculations that the resulting compounds are ferrimagnets. When the total number of valence electrons reaches the magic number of 24 the Fe-doped compounds are semi-metals and thus non-magnetic while the Co-doped ones show the desirable half-metallic antiferromagnetic character. The compounds are very likely to be synthesized experimentally since the parent compounds, Mn2VAl and Co2VAl, have been already grown in the Heusler L21 lattice structure.

Abstract.Using a state-of-the-art full-potential electronic structure method within the local spin density approximation, we study the electronic and magnetic structure of Mn 2 V-based full Heusler alloys: Mn 2 VZ (Z=Al, Ga, In, Si, Ge, and Sn). We show that small expansion of the calculated theoretical equilibrium lattice constants restores the half-metallic ferrimagnetism in these compounds. Moreover a small degree of disorder between the V and Z atoms, although iduces some states within the gap, it preserves the Slater-Pauling behaviour of the spin magnetic moments and the alloys keep a high degree of spin-polarisation at the Fermi level opening the way for a half-metallic compensated ferrimagnet.

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Heusler alloys containing Co and Mn are amongst the most heavily studied half-metallic ferromagnets for future applications in spintronics. Using state-of-the-art electronic structure calculations, we investigate the effect of doping and disorder on their electronic and magnetic properties. Small degrees of doping by substituting Fe or Cr for Mn scarcely affect the half-metallicity. A similar effect is also achieved by mixing the sublattices occupied by the Mn and sp atoms. Thus the half-metallicity is a robust property of these alloys.PACS numbers: 75.47. Np, 75.50.Cc, 75.30.Et The intensive development of electronics based on the combination of magnetic and semiconducting materials has brought in the center of scientific research new exotic materials. Half-metallic ferromagnets, which were first predicted by de Groot and collaborators in 1983, 1 have the peculiarity that the band-structure of the minorityspin electrons is semiconducting while of the majorityspin electrons is a normal metallic one. Such materials could maximize the efficiency of spintronic devices.2 Several Heusler compounds like NiMnSb and Co 2 MnSi have been predicted to be half-metals. 3Ishida and collaborators were, to the best of our knowledge, the first to study by means of ab-initio calculations the full-Heusler compounds of the type Co 2 MnZ, where Z stands for Si and Ge, and have shown that they are half-metals.4 Later the origin of half-metallicity in these compounds has been largely explained.3 Many experimental groups during the last years have worked on these compounds and have tried to synthesize them mainly in the form of thin films and incorporate them in spintronic devices. The group of Westerholt has extensively studied the properties of Co 2 MnGe films and they have incorporated this alloy in the case of spinvalves and multilayer structures.5 The group of Reiss managed to create magnetic tunnel junctions based on Co 2 MnSi.6 A similar study of Sakuraba and collaborators resulted in the fabrication of magnetic tunnel junctions using Co 2 MnSi as one magnetic electrode and Al-O as the barrier (Co 75 Fe 25 is the other magnetic electrode) and their results are consistent with the presence of half-metallicity for Co 2 MnSi.7 Dong and collaborators recently managed to inject spin-polarized current from Co 2 MnGe into a semiconducting structure.8 Finally Kallmayer et al. studied the effect of substituting Fe for Mn in Co 2 MnSi films and have shown that the experimental extracted magnetic spin moments are compatible with the half-metallicity for small degrees of doping.

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