Effects of electron-phonon scattering on half-metallicity of Co2MnSi

Abstract

Although the existence of a wide gap in the minority spin channel and its half- metallicity ofL21 Co2MnSi are well established in first-principles calculations, these properties turn outrather fragile under realistic situations such as device structures. It has been pointed out thatchemical disorders and defects easily degrade the half-metallic nature of this material. Thesedegradations are structure oriented and therefore static. This means once a perfect structureis attained, there are no reasons of this kind of degradation of the half-metallicity. However,there still exist dynamical effects, caused mainly by phonons and magnons at finitetemperature. In this paper we discuss the effects of electron-phonon scattering on half-metallicity on the basis of first-principles calculations. The phonons are treated as local andstatic (adiabatic) [1], where correlation of the displacements between neighboring sites as wellas dynamical effects is neglected. Then, the phonons are expressed as random displacementsof atoms from their equilibrium positions. Using the distribution of the atomic displacement, theelectronic structures of the system at finite temperature are calculated by regarding thesystem as a disordered system with randomly distributed atomic positions. This kind ofrandomness can be treated using KKR-CPA code [2]. The results show that even at 300 K,the perfect half-metallicity is lost (Fig.1), showing that the effects of phonons are important atusual operating temperatures of devices. The effects on the GMR will be discussed.[1] S. Kou and H. Akai, Solid State Commun. 276, 1 (2018). [2] H. Akai, http://kkr.issp.u-tokyo.ac.jp