Localized Singlets and Ferromagnetic Fluctuations in the Dilute Magnetic Topological Insulator Sn$_{0.95}$Mn$_{0.05}$Te

TL;DR

This study investigates magnetic excitations in Sn$_{0.95}$Mn$_{0.05}$Te, revealing slow ferromagnetic fluctuations and localized antiferromagnetic Mn-Mn dimers, highlighting complex magnetic interactions without long-range order.

Contribution

It provides the first inelastic neutron scattering analysis of magnetic excitations in a dilute magnetic topological insulator, showing coexistence of ferromagnetic fluctuations and localized dimers.

Findings

Detection of slow ferromagnetic fluctuations below 70 μeV.

Observation of sharp peaks from antiferromagnetically coupled Mn-Mn dimers.

Absence of long-range ferromagnetic order above 2 K.

Abstract

The development of long-range ferromagnetic (FM) order in dilute magnetic topological insulators can induce dissipationless electronic surface transport via the quantum anomalous Hall effect. We measure the magnetic excitations in a prototypical magnetic topological crystalline insulator, Sn$_{0.95}$Mn$_{0.05}$Te, using inelastic neutron scattering. Neutron diffraction and magnetization data indicate that our Sn$_{0.95}$Mn$_{0.05}$Te sample has no FM long-range order above a temperature of 2 K. However, we observe slow, collective FM fluctuations ($<$~70 $\mu$eV), indicating proximity to FM order. We also find a series of sharp peaks originating from local excitations of antiferromagnetically (AF) coupled and isolated Mn-Mn dimers with $J_{\rm AF}=460$~$\mu$eV\@. The simultaneous presence of collective and localized components in the magnetic spectra highlight different roles for substituted Mn ions, with competition between FM order and the formation of AF-coupled Mn-Mn dimers.