Controlling Magnonic Spin Current through Magnetic Anisotropy and Gilbert Damping

Abstract

The magnon propagation length, (MPL) of a ferro/ferrimagnet (FM) is one of the key factors that controls the generation and propagation of thermally-driven spin current in FM/heavy metal (HM) bilayer based spincaloritronic devices. Theory predicts that for the FM layer, MPL is inversely proportional to the Gilbert damping (alpha) and the square root of the effective magnetic anisotropy constant (K_eff). However, direct experimental evidence of this relationship is lacking. To experimentally confirm this prediction, we employ a combination of longitudinal spin Seebeck effect (LSSE), transverse susceptibility, and ferromagnetic resonance experiments to investigate the temperature evolution of MPL and establish its correlation with the effective magnetic anisotropy field, H_K^eff (proportional to K_eff) and alpha in Tm3Fe5O12 (TmIG)/Pt bilayers. We observe concurrent drops in the LSSE voltage and MPL below 200 K in TmIG/Pt bilayers regardless of TmIG film thickness and substrate choice and attribute it to the noticeable increases in H_K^eff and alpha that occur within the same temperature range. This study not only highlights the ability to manipulate MPL by controlling H_K^eff and alpha in FM/HM based spincaloritronic nanodevices, but also shows that the tuning of alpha is more effective than H_K^eff in controlling MPL and, hence, the spincaloritronic efficiency.Comment: 5 main text figure