室温におけるフェリ磁性体中におけるディラック表面状態によるスピンダイナミクス

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  • Dirac surface state-modulated spin dynamics in a ferrimagnetic insulator at room temperature

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This work demonstrates markedly modified spin dynamics of magnetic insulator (MI) by the spin momentum-locked Dirac surface states of the adjacent topological insulator (TI). As the Bi concentration $x$ is systematically tuned in 5-nm-thick (Bi$_{x}$Sb$_{1-x}$)$_{2}$Te$_{3}$ TI films, the weight of the surface relative to bulk states peaks at $x$ = 0.32 when the chemical potential approaches the Dirac point. At this concentration, the Gilbert damping constant of the precessing magnetization in 10-nm-thick Y$_{3}$Fe$_{5}$O$_{12}$ MI films in the MI/TI heterostructures is enhanced by an order of magnitude, the largest among all concentrations. In addition, the MI acquires additional strong magnetic anisotropy that favors the in-plane orientation with similar Bi concentration dependence. These extraordinary effects of the Dirac surface states distinguish TI from other materials such as heavy metals in modulating spin dynamics of the neighboring magnetic layer.

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