Origin and properties of the gap in the half-ferromagnetic Heusler alloys

Abstract

We study the origin of the gap and the role of chemical composition in the half-ferromagnetic Heusler alloys using the full-potential screened KKR method. In the paramagnetic phase the C1 b compounds, like NiMnSb, present a gap. Systems with 18 valence electrons, Zt, per unit cell, like CoTiSb, are semiconductors, but when Zt > 18 antibonding states are also populated, thus the paramagnetic phase becomes unstable and the half-ferromagnetic one is stabilized. The minority occupied bands accommodate a total of nine electrons and the total magnetic moment per unit cell in µB is just the difference between Zt and 2 × 9. While the substitution of the transition metal atoms may preserve the half-ferromagnetic character, substituting the sp atom results in a practically rigid shift of the bands and the loss of half-metallicity. Finally we show that expanding or contracting the lattice parameter by 2% preserves the minority-spin gap.

Surface properties of the half-and full-Heusler alloys

“…In the left panel of figure 2 I present the atomand spin-projected density of states (DOS) for the Mn and Sb atoms in the surface layer and the Ni and vacant site in the subsurface layer for the MnSb terminated NiMnSb(001) surface, and in the right panel of the same figure I present the atomand spin-projected DOS of the surface and the subsurface layers for the Ni terminated surface. In both cases I compare the surface DOS with the bulk calculations (dashed line) [37].…”

First-principles study for electronic structure and physical property of Co-based Heusler alloys

“…In the L2 1 and B2 structure, it is confirmed that their DOS of the minority spin states have an energy gap at the Fermi level and become a half-metal. The energy gap around the Fermi level of Co-based full-Heusler alloys in the ordered L2 1 structure is mainly constructed by the states based on the second nearest Co-Co hybridization [13]. So the half-metallic property of the B2 structure is still preserved due to the ordering of the Co-sub-lattice as well as Co 2 CrAl [6].…”

“…3, there is a linear increase of the magnetic moments in L2 1 and B2 structure, which is proportional to the valence electrons number. This tendency is one of the features of half-metals that is so called the Slater-Pauling behavior, and the magnetic moment of half-metallic full-Heusler alloys is expressed in N v −24 µ B [13]. In the region of Co 2 Mn 1−y Fe y Si, however, the Slater-Pauling behavior is not obtained, and the magnetic moments have a peak about 5.2 µ B around y = 0.4.…”

Bias-voltage-dependence of magnetoresistance for epitaxial Fe/MgO/Co2MnSn tunnel junctions

“…Half metallic materials, which exhibit perfect spin polarization at the Fermi energy, are expected to be ideal materials to achieve large TMR ratio. Recently, TMR ratio of above 300 % at RT [4] was achieved in MTJs using Co-based Heusler alloys [4][5][6][7] which are theoretically predicted as half metallic materials [8][9]. On the other hand, we have reported that Co 2 MnSn Heusler alloy films with relatively uniform local magnetism can be prepared when the films are grown by atomically controlled alternate deposition at 400 o C [10].…”