Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order

Abstract

Half-metallicity and low magnetic damping are perpetually sought for in spintronics materials and full Heusler alloys in this respect provide outstanding properties. However, it is challenging to obtain the well-ordered half-metallic phase in as-deposited full Heusler alloys thin films and theory has struggled to establish a fundamentals understanding of the temperature dependent Gilbert damping in these systems. Here we present a study of the temperature dependent Gilbert damping of differently ordered as-deposited Co 2 FeAl full Heusler alloy thin films. The sum of inter-and intraband electron scattering in conjunction with the finite electron lifetime in Bloch states govern the Gilbert damping for the wellordered phase in contrast to the damping of partially-ordered and disordered phases which is governed by interband electronic scattering alone. These results, especially the ultralow room temperature intrinsic damping observed for the well-ordered phase provide new fundamental insights to the physical origin of the Gilbert damping in full Heusler alloy thin films.

Interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films

“…A piece of the CFA sample was annealed at 500 • C ex situ, which reduced the inhomogenoeus broadening to ∼45 Oe (still a relatively large value) and increased the Gilbert damping to α 001 = 1.1 × 10 −3 (similar behavior in CFA was seen in Ref. [21]). The constraint of α 001 < 8 × 10 −4 is among the lowest of reported Gilbert damping constants for metallic ferromagnets, but the α ∼ 10 −4 range is not unexpected based on Kamberský model calculations performed for similar full-Heusler compounds [9] or other recent experimental reports [22,23].…”

Thickness dependence of dynamic magnetic properties of soft (FeCo)-Si alloy thin films

“…For a two-magnon scattering contribution of strictly interfacial origin, one expects this linewidth contribution to scale like the square of the inverse film thickness. 9,18,23,26,42 However, for this sample series, such a dependence is not observed. In particular, the thickest film exhibits a significantly larger ∆H 2m than what one would expect based on the rest of the series.…”

“…The effective damping parameter we extracted here contains both intrinsic and extrinsic contributions such as two-magnon scattering, 23,24 eddycurrent damping, 25,26 and radiative damping. 26,27 The intrinsic damping will be lower than the effective damping, especially those of the thicker samples, which suffer from a larger eddy-current damping. The significant increase of the effective damping parameter increase for the 4 nm thick film has two potential origins: two-magnon scattering and spin pumping.…”

Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Film Heterostructures

“…However, in them the film thicknesses were several tens of nm and Curie temperatures (T C ) were lower than 300 K, i.e., 35 K, 29 K, 270 K and 280 K, respectively. On the other hand, the present work is based on the Co 2 FeAl (T C ~1000 K 20 ) thin films having perpendicular magnetic anisotropy and skyrmions are observed in a robust manner at room temperature. Further, in all these non-centrosymmetric cases, the samples were cooled to a low temperature and/or required the presence of a high magnetic field to reveal the existence of the skyrmionic state.…”

“…To the best of our knowledge, the existence of skyrmions in high spin-polarized materials, i . e ., full Heusler alloys such as Co 2 FeAl (CFA) which possess low damping constant 34 , high Curie temperature 20 , large spin polarization 43 and tunable spin-dynamics properties 44,45 is yet to be reported. Despite the rapidly increasing number of experimental studies for gaining further insight into understanding the stabilization of skyrmions in ultrathin films, the robust formation of skyrmions at room temperature in large continuous thin films continues to be an exciting area.…”