Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first principles

Galanakis, I.; Mavropoulos, Phivos

doi:10.1088/0953-8984/19/31/315213

Cited by 173 publications

(106 citation statements)

References 80 publications

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“…The origin of the HM gap in Heusler alloys has been well understood and the reader is referred to Ref. 25 since the same discussion is valid for the present systems.…”

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confidence: 80%

Nonzero macroscopic magnetization in half-metallic antiferromagnets at finite temperatures

Şaşıoğlu

2009

Phys. Rev. B

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Combining density-functional theory calculations with many-body Green's-function technique, we reveal that the macroscopic magnetization in half-metallic antiferromagnets does not vanish at finite temperature as for the T = 0 limit. This anomalous behavior stems from the inequivalent magnetic sublattices which lead to different intrasublattice exchange interactions. As a consequence, the spin fluctuations suppress the magnetic order of the sublattices in a different way leading to a ferrimagnetic state at finite temperatures. Computational results are presented for the half-metallic antiferromagnetic CrMnZ ͑Z =P,As,Sb͒ semi-Heusler compounds. DOI: 10.1103/PhysRevB.79.100406 PACS number͑s͒: 75.50.Cc, 71.15.Mb, 75.30.Et, 75.60.Ϫd Half-metallic antiferromagnets ͑HM-AFMs͒ are considered to be the most promising class of materials for spintronics applications.1,2 A HM-AFM material is not antiferromagnetic in the usual sense of the term; it is a special case of a ferrimagnet with compensated sublattice magnetization. The existence of the gap in one of the spin channels ͑either up or down͒ leads to the complete cancellation of the magnetic moments at zero temperature with a 100% spin polarization of the charge carriers at the Fermi level. In conventional AFMs the macroscopic spin polarization is zero due to the spin rotational symmetry with the exception of the compounds with broken inversion symmetry such as ␣-Fe 2 O 3 in which spin-orbit gives rise to weak ferromagnetism ͑0.002 B ͒ due to the canting of the magnetic moments. 3,4The HM-AFM materials provide several advantages in device applications with respect to the half-metallic ferromagnets ͑HM-FMs͒. For example, they would be perfectly stable spin-polarized electrodes in a junction device. These materials do not give rise to stray fields, and thus no magnetic domain walls are formed. Besides applications in spintronics, HM-AFMs provide a possibility of "single spin superconductivity" due to the spin triplet ͑S =1͒ pairing in metallic channel. 5The possible existence of HM-AFM was pointed out by van Leuken and de Groot 6 in 1995. Based on first-principles calculations authors proposed CrMnSb and V 7 MnFe 8 Sb 7 In as candidates for HM-AFMs. Later, Pickett suggested that also the cubic double perovskites La 2 VCuO 6 , La 2 MnVO 6 , and La 2 MnCoO 6 are HM-AFMs. 7 Since then substantial effort has been devoted to find materials with HM antiferromagnetic characteristics. Predicted promising systems include double perovskites, 8,9 thiospinels, 10 tetrahedrally coordinated transition-metal-based chalcopyrites, 11 fullHeusler alloys, 12,13 and monolayer superlattices. 14 Not only ordered but also several disordered systems have been shown to be HM-AFMs. [15][16][17][18][19][20] In spite of substantial theoretical efforts for designing materials with HM-AFM characteristics and the study of their ground-state electronic and magnetic properties, only few works exist addressing the exchange interactions and magnetic phase transition temperatures in these systems. 19,20 ...

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“…The origin of the HM gap in Heusler alloys has been well understood and the reader is referred to Ref. 25 since the same discussion is valid for the present systems.…”

mentioning

confidence: 80%

Nonzero macroscopic magnetization in half-metallic antiferromagnets at finite temperatures

Şaşıoğlu

2009

Phys. Rev. B

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“…One of the most interesting concepts in spintronics is the half-metallicity [4,5,6,7,8,9,10]. Halfmetals are hybrids between normal metals and semiconductors.…”

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confidence: 99%

Engineering the electronic, magnetic, and gap-related properties of the quinternary half-metallic Heusler alloys

Özdoğan

Şaşıoğlu²,

Galanakis

2008

Journal of Applied Physics

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Abstract. We review the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co 2 [Cr 1−x Mnx][Al 1−y Siy] employing three different approaches : (i) the coherent potential approximation (CPA), (ii) the virtual crystal approximation (VCA), and (iii) supercell calculations (SC). All three methods give similar results and the local environment manifested itself only for small details of the density of states. All alloys under study are shown to be halfmetals and their total spin moments follow the so-called Slater-Pauling behavior of the ideal half-metallic systems. We especially concentrate on the properties related to the minority-spin band-gap. We present the possibility to engineer the properties of these alloys by changing the relative concentrations of the lowvalent transition metal and sp atoms in a continuous way. Our results show that for realistic applications, ideal are the compounds rich in Si and Cr since they combine large energy gaps (around 0.6 eV), robust half-metallicity with respect to defects (the Fermi level is located near the middle of the gap) and high values of the majority-spin density of states around the Fermi level which are needed for large values of the perfectly spin-polarized current in spintronic devices like spin-valves or magnetic tunnel junctions.

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“…At first, such a metal with perfect spin polarization was termed a "half-metallic antiferromagnet," although the two sublattices are strictly inequivalent, structurally and often chemically. If it existed, it could be useful because the material would be fully spin polarized, yet would be free from shape anisotropy and create no stray field [14].Although there have been numerous electronic structure calculations for hypothetical compounds with perfectly compensated ferrimagnetism [1,[14][15][16][17][18][19], all attempts to make them in practice have failed [14]. Nature seems to shun this unusual variety of magnetic order.…”

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CubicMn2GaThin Films: Crossing the Spin Gap with Ruthenium

et al. 2014

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Cubic Mn 2 Ga films with the half-Heusler C1 b structure are grown on V (001) epitaxial films. The phase is a soft ferrimagnet, with Curie temperature T C ¼ 225 K and magnetization M s ¼ 280 kA m −1 , equivalent to 1.65 μ B per formula. Adding ruthenium leads to an increase of T C up to 550 K in cubic Mn 2 Ru x Ga films with x ¼ 0.33 and a collapse of the net magnetization. The anomalous Hall effect changes sign at x ¼ 0.5, where the sign of the magnetization changes and the magnetic easy direction flips from in plane to perpendicular to the film. The Mn 2 Ru 0.5 Ga compound with a valence electron count of 21 is identified as a zero-moment ferrimagnet with high spin polarization, which shows evidence of half-metallicity. DOI: 10.1103/PhysRevLett.112.027201 PACS numbers: 75.30.Gw, 75.60.Ej, 75.70.-i Cubic ferrimagnetic Heusler compounds are a rich family of magnetic materials [1], that can exhibit a higher spin polarization at the Fermi level than any binary 3d ferromagnetic alloy. Several Co 2 YZ compounds, for example, are thought to be half-metals with a gap in the spin-polarized density of states for one spin direction [1][2][3], which makes them particularly suitable for spin valves [4,5] and magnetic tunnel junctions [6,7]. The net spin in Bohr magnetons per unit cell should be an integer for a stoichiometric half-metal, and the moments m of X 2 YZ half-metals with the L2 1 structure are found to follow a modified Slater-Pauling curve [8].where N v is the number of valence electrons per formula. The ordered L2 1 structure illustrated in Fig. 1 Fig. 1(b)], but a variant has X and Y atoms ordered on 8c sites (4c=4d), with 4b sites vacant. The modified Slater-Pauling rule is thenThe original example of a half-metal was NiMnSb (m ¼ 4 μ B ) [12,13].When X and Y atoms carry a moment and the X − Y coupling is antiferromagnetic, the compounds are ferrimagnets. Half-metallic full Heuslers with N v ¼ 24 and half Heuslers with N v ¼ 18 are particularly interesting, because the ferrimagnetism should then be perfectly compensated, with net spin m ¼ 0 μ B . At first, such a metal with perfect spin polarization was termed a "half-metallic antiferromagnet," although the two sublattices are strictly inequivalent, structurally and often chemically. If it existed, it could be useful because the material would be fully spin polarized, yet would be free from shape anisotropy and create no stray field [14].Although there have been numerous electronic structure calculations for hypothetical compounds with perfectly compensated ferrimagnetism [1,[14][15][16][17][18][19], all attempts to make them in practice have failed [14]. Nature seems to shun this unusual variety of magnetic order. Half-metallicity is a zero-temperature property, which can be spoiled by imperfect atomic order of the X, Y, and Z atoms in the structure, spin-orbit coupling, or finite temperature, either due to smearing of the Fermi surface or to the different temperature dependence of the magnetization of the two sublattice magnetizations [16]. Candidate ma...

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Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first principles

Cited by 173 publications

References 80 publications

Nonzero macroscopic magnetization in half-metallic antiferromagnets at finite temperatures

Nonzero macroscopic magnetization in half-metallic antiferromagnets at finite temperatures

Engineering the electronic, magnetic, and gap-related properties of the quinternary half-metallic Heusler alloys

CubicMn2GaThin Films: Crossing the Spin Gap with Ruthenium

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