Experimental Verification of Van Vleck Nature of Long-Range Ferromagnetic Order in Vanadium-Doped Three-Dimensional Topological Insulator Sb$_{2}$Te$_{3}$

TL;DR

This study uses high-resolution EELS to confirm that the long-range ferromagnetic order in V-doped Sb2Te3 is of van Vleck type, with core-level contributions verified through spectral analysis and magnetotransport measurements.

Contribution

It provides direct experimental evidence of van Vleck-type ferromagnetism in a three-dimensional topological insulator, highlighting the role of core states in magnetic ordering.

Findings

Van Vleck ferromagnetism confirmed in V-doped Sb2Te3.

Core-level spectral changes indicate magnetic transition at low temperature.

Magnetotransport supports the spectral evidence of ferromagnetic order.

Abstract

We demonstrate by high resolution low temperature electron energy loss spectroscopy (EELS) measurements that the long range ferromagnetic (FM) order in vanadium (V)-doped topological insulator Sb$_2$Te$_3$ has the nature of van Vleck-type ferromagnetism. The positions and the relative amplitudes of two core-level peaks (L$_3$ and L$_2$) of the V EELS spectrum show unambiguous change when the sample is cooled from room temperature to T=10K. Magnetotransport and comparison of the measured and simulated EELS spectra confirm that these changes originate from onset of FM order. Crystal field analysis indicates that in V-doped Sb$_2$Te$_3$, partially filled core states contribute to the FM order. Since van Vleck magnetism is a result of summing over all states, this magnetization of core level verifies the van Vleck-type ferromagnetism in a direct manner.