Temperature-dependent spin polarization of Heusler Co2MnSi from the disordered local-moment approach: Effects of atomic disordering and nonstoichiometry

Abstract

Half-metallic ferromagnets have been widely investigated by first-principles density-functional theory (DFT) calculations, but extending such studies to investigate spin-polarization at finite temperatures is still challenging due to the difficulty of incorporating temperature effects appropriately. We present DFT calculations, based on a Green's function formulation, which include thermal effects via the disordered local-moment method to address this issue. The calculations are carried out for Heusler Co 2 MnSi alloys in order to investigate the temperature dependence of spin polarization, where atomic-disordering and nonstoichiometric effects are taken into account. Our results show that the spin polarization strongly depends on temperature and that a Co d-orbital effect plays a key role in this effect. Furthermore, we find that the temperature-dependent spin polarization of Co 2 MnSi can be improved by reducing the Co content and incorporating extra Mn.

Crucial role of interfacial $s$-$d$ exchange interaction in the temperature dependence of tunnel magnetoresistance

“…As shown in Fig. 1(b), increasing the temperature enhances spin fluctuations in d-electron states, as suggested in previous studies [16][17][18][19]. We find that such spin fluctuations propagate from d-to s-electron states through the sd exchange interaction.…”

“…A clue to explain this phenomenon is conduction sp-electron states in ferromagnets; several experiments [7,10] have shown that sp-electron states with smaller effective mass than d-electron states provide dominant contributions to transport properties of MTJs. However, most previous theories [12][13][14][15][16][17][18][19] have focused only on delectron states and dd exchange interaction between d electrons on neighboring sites. This is because d-electron states have large density of states around the Fermi level and play the main role for static magnetic properties in bulk ferromagnets at finite temperature.…”

“…For example, the Curie temperatures of 3d transition metals have been estimated by the Heisenberg model with the dd exchange interaction [12][13][14][15]. Moreover, temperature dependencies of spin polarizations in Heusler alloys have been understood by spin fluctuations in d-electron states [16][17][18][19]. In contrast, since transport properties in MTJs can be dominated by sp-electron states as mentioned above, we need to clarify how these states correlate with temperature dependence of the TMR ratio.…”

Effect of Fe atomic layers at the ferromagnet–semiconductor interface on temperature-dependent spin transport in semiconductors

“…In addition, since the FM layer in this study is composed of one of the Co-based Heusler alloys, we should consider the influence of the structural disorder in the Co-based Heusler alloy on the temperature-dependent P inj=det in FM/SC LSV devices. Actually, recent theoretical studies have already discussed the correlation between the atomic-level disorder including nonstoichiometries in Co-based Heusler alloys and the bulk P with increasing T. 52,53 For high-performance FM-SC hybrid devices above room temperature, it will be essential to discuss the influence of the atomic disorder near the interfaces on the temperature-dependent P inj=det in future.…”

MARMOT: magnetism, anisotropy, and more, using the relativistic disordered local moment picture at finite temperature

“…Here, S is the spin operator. The value of this quantity at the Fermi level (E = E F ) is of particular interest when investigating magnetoresistive devices [30].…”