[22p-A205-1~18] 10.2 Fundamental and exploratory device technologies for spin

▲ [22p-A205-18] Theory of persistent coherence in excited magnetic particles

〇(P)Mehrdad Elyasi¹, Kei Yamamoto⁴, Tomosato Hioki^1,2, Takahiko Makiuchi², Hiroki Shimizu², Koujiro Hoshi^2,3, Naoto Yokoi^2,3, Gerrit E. W. Bauer¹, Eiji Saitoh^1,2,3,4 (1.AIMR Tohoku Univ., 2.Dept. Appl. Phys., Univ. Tokyo, 3.Inst. AI and Beyond, Univ. Tokyo, 4.JAEA)

Keywords:Magnons, Nonlinearity, Coherence

The spin-lattice relaxation governs the intrinsic Gilbert damping of the room temperature magnetization dynamics in magnetic insulators such as yttrium iron garnet. However, strongly anisotropic magnon dispersion and inherent nonlinearities can cause significantly larger broadening. The Kittel mode can decay by a three magnon scattering process when a pair of nonzero wave vector (valley) magnons at half its frequency exist. The latter in turn feel only the intrinsic damping. Here we present calculations of the transient magnetization dynamics including the leading nonlinear magnon-magnon interactions. We predict a Kittel mode amplitude that persists much longer than could be expected from the FMR line shape, in agreement with AC spin pumping experiments by Makiuchi et al.. We explain the effect in terms of a coherent hybridization of the Kittel mode with the long-lived 3-magnon driven pair states.