Bound Magnetic Polarons in the 3d-electron Ferromagnetic Spinel Semiconductor CdCr$_2$Se$_4$

TL;DR

This study uses muon spin spectroscopy to detect magnetic polarons in the ferromagnetic spinel CdCr$_2$Se$_4$, revealing electron localization and magnetic interactions up to room temperature.

Contribution

It provides direct experimental evidence of bound magnetic polarons in CdCr$_2$Se$_4$ at high temperatures, highlighting the role of exchange interactions in electron localization.

Findings

Magnetic polarons detected up to 300 K

Electron wave function confined within 0.3 nm

Strong exchange interaction with Cr$^{3+}$ ions

Abstract

Muon spin rotation/relaxation spectroscopy %(supported by magnetization measurements) has been employed to study electron localization around a donor center - the positive muon - in the 3d magnetic spinel semiconductor CdCr$_2$Se$_4$ at temperatures from 2 to 300 K in magnetic fields up to 7 T. A bound state of an electron around a positive muon - a magnetic polaron - is detected far above the ferromagnetic transition up to 300 K. Electron localization into a magnetic polaron occurs due to its strong exchange interaction with the magnetic 3d electrons of local Cr$^{3+}$ ions, which confines its wave function within R\approx 0.3 nm, allowing significant overlap with both the nearest and next nearest shells of Cr ions.