Origin of the magnetic moment enhancement of the ordered Fe₅₀Co₅₀ alloys

Abstract

PACS 75.50.Bb We investigated the physical origin of the magnetic moment enhancements of the ordered Fe 50 Co 50 alloys with B2 and L1 0 structures by using the all-electron total-energy full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation. Pure Fe and Co with the WignerSeitz radii taken from the alloys are also calculated for comparsion. It is confirmed that the magnetic moments of Fe in the alloys are enhanced significantly, while those of Co remain almost unchanged. The Fe magnetic moment enhancement in the alloy originates from "spin-flipping" of t 2g electrons caused by the increase of the exchange splitting which makes the majority d electrons filled completely. In the case of the Co magnetic moment in the alloys, the spin-up d band is already filled up in the pure phases, hence the magnetic moment stability against the alloy formation is preserved.1 Introduction Iron group transition metal alloys have attracted much attention since they are not only considered as prototype materials for band ferromagnetism but also used for magnetic recording media. Based on the well-known Slater-Pauling curve [1], it is expected that Fe-Co alloy with a specific composition exhibits the largest magnetic moment among various iron group alloys. The Fe-Co alloys are popularly used soft magnetic materials [2, 3] for ultrahigh-density magnetic recording media because of their relatively low coercive fields. There was also a report on possible nanoscale applications by forming Fe-Co nanowires in self-assembled arrays [4].It is known that CsCl-type (B2 structure) Fe-Co alloys are stable up to Co concentration of 70%, and their magnetic moments exhibit maximum around at the Co concentration of 30%. Neutron diffraction experiments [5,6] indicate that, as the composition changes, the magnetic moment of the Co site remains roughly constant of 1.8 µ B , but the magnetic moment of the Fe site increases from 2.2 µ B (pure bcc Fe) to about 3.0 µ B . As a result, the average magnetization of the Fe-Co alloys is much larger than that of the constituent elements. In this paper, we investigate the physical origin of the magnetic moment enhancements of the ordered Fe 50 Co 50 alloys, by using the all-electron total-energy full-potential linearized augmented plane wave (FLAPW) method [7] within the generalized gradient approximation (GGA) [8] to exchange correlation potential.

Effect of local atomic disorder on the half-metallicity of full-Heusler Co 2 FeSi alloy: a first-principles study

“…In the Co-Si disordered system, when a Co was swapped by a nearest-neighbouring Si, the disordered Co has seven Co and one Si as the 1nn, which is similar to that of the bcc Co where the Co has eight Co atoms as the 1nn. Indeed, the magnetic moment of disordered Co atom is close to that (1.81 µ B ) of the bcc Co. [26] The study of effect of disorder on the half-metallic character of Co 2 MnSi is also suggested that the 1nn mainly dictates the behaviour of the magnetic moments of transition metals. [15] For the Fe-Si disorder, the local magnetic moments of the Co and Fe atoms are affected very little, and the total magnetic moment remains at an integer value of 6.00 µ B , as in the ordered system, thus, we can expect that the Co 2 FeSi keeps its halfmetallicity against this kind of disorder.…”