Dirac-Surface-State Modulated Spin Dynamics in a Ferrimagnetic Insulator at Room Temperature

TL;DR

This study reveals how Dirac surface states in topological insulators significantly alter spin dynamics in adjacent magnetic insulators at room temperature, with potential for advanced spintronic devices.

Contribution

It demonstrates the modulation of spin dynamics by Dirac surface states in topological insulators, showing a peak effect at a specific Bi concentration, which is a novel finding.

Findings

Enhanced Gilbert damping by an order of magnitude at optimal Bi concentration

Induction of strong magnetic anisotropy in the magnetic insulator

Distinct effects of Dirac surface states compared to heavy metals

Abstract

This work demonstrates dramatically modified spin dynamics of magnetic insulator (MI) by the spin-momentum locked Dirac surface states of the adjacent topological insulator (TI) which can be harnessed for spintronic applications. As the Bi-concentration x is systematically tuned in 5 nm thick (BixSb1-x)2Te3 TI film, 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 Y3Fe5O12 MI film 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.