Spin dynamics and magnetic interactions of Mn dopants in the topological insulator Bi$_2$Te$_3$

TL;DR

This study investigates the magnetic interactions and spin dynamics of Mn-doped Bi2Te3 topological insulators, revealing ferromagnetic ordering, carrier interactions, and persistent magnetic correlations above the Curie temperature.

Contribution

The paper provides new insights into the magnetic coupling mechanisms and spin behavior of Mn dopants in Bi2Te3, using ESR and magnetization measurements.

Findings

Ferromagnetic transition at x≥0.04 around 12 K

Mn moments interact via RKKY-type coupling

Magnetic correlations persist above T_C

Abstract

The magnetic and electronic properties of the magnetically doped topological insulator Bi$_{\rm 2-x}$Mn$_{\rm x}$Te$_3$ were studied using electron spin resonance (ESR) and measurements of static magnetization and electrical transport. The investigated high quality single crystals of Bi$_{\rm 2-x}$Mn$_{\rm x}$Te$_3$ show a ferromagnetic phase transition for $x\geq 0.04$ at $T_{C}\approx 12$ K. The Hall measurements reveal a p-type finite charge-carrier density. Measurements of the temperature dependence of the ESR signal of Mn dopants for different orientations of the external magnetic field give evidence that the localized Mn moments interact with the mobile charge carriers leading to a Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a low-dimensional character of magnetic correlations that persist far above the ferromagnetic ordering temperature.