Colossal Gilbert Damping Anisotropy in Heusler‐Alloy Thin Films

Abstract

Hence, it is crucial to manipulate the Gilbert damping on demand for versatile spintronic applications. Extensive efforts have been made including material optimization, [7][8][9][10][11] interface engineering, [12][13][14][15] spin torque, [16][17] and damping anisotropy. [18][19][20][21] Among these approaches, utilizing intrinsic Gilbert damping anisotropy, without requiring multiple magnetic devices or large critical current density, has attracted considerable attention. Such a method allows continuous damping manipulation via rotating the magnetization direction.Heusler compounds constitute a prominent class of magnetic materials featuring high spin polarization [22][23][24] and ultralow magnetic damping [25][26] in spintronics. Although many theoretical works [27][28][29] predict the existence of Gilbert damping anisotropy, there has been a lack of strong experimental evidence in Heusler alloys. For instance, the earlier works, such as Co 2 FeSi, [30] Co 2 MnSi, [31] and Co 2 FeAl, [25,32,33] did not provide any convincing analysis of the intrinsic damping anisotropy. At the same time, those reported effects [30][31][32][33] are too weak to develop novel functionality in spintronic devices. Hence, seeking new Heusler ingredients with significant Gilbert damping anisotropy has become a tremendous challenge. Additionally, the key mechanism behind this effect remains unexplored in Heusler alloys.In this work, we have deposited the Heusler-alloy Co 3−x Fe x Al (x = 1-2) single crystalline thin films using the molecular beam epitaxy (MBE) technique. The in-plane angular dependent ferromagnetic resonance (FMR) measurements show that the anisotropic damping exhibits fourfold symmetry and the maximal ratio of up to 1400% for the optimized sample Co 1.4 Fe 1.6 Al, which is nearly three times higher than the highest value of 420% reported in metallic ferromagnets. [34] Furthermore, according to anisotropic magnetoresistance (AMR) measurement and first-principles calculation, we ascribed such colossal anisotropy of Gilbert damping to the variation of the spin-orbit coupling (SOC). Our results help explore the larger anisotropic damping ratio in Heusler alloys and understand its mechanism for spintronic applications. Results and Discussion Anisotropic Magnetization Relaxation of Co 3−x Fe x Al FilmsHeusler alloy Co 3−x Fe x Al (x = 1-2) thin films were grown on the MgO (001) substrates by MBE. The details of structural characteristics Manipulating Gilbert damping is of critical importance in spintronic devices. Here, this work reports the damping anisotropy of Heusler-alloy Co 3−x Fe x Al single crystalline thin films using inductive ferromagnetic resonance. A colossal Gilbert damping anisotropy ratio of up to 1400%, nearly three times higher than the highest value reported among known metallic ferromagnets, is observed in the optimized sample Co 1.4 Fe 1.6 Al. The Gilbert damping anisotropy with strong fourfold symmetry is attributed to the variation of the spin-orbit coupling, which is further corroborated by the cur...