Reversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals

TL;DR

This study demonstrates reversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals, closely linked to oxygen vacancies and free carriers, with magnetic properties controllable via annealing processes.

Contribution

It provides evidence that oxygen vacancies induce ferromagnetism in SrTiO3, and shows this magnetism can be reversibly controlled through annealing, advancing understanding of oxide-based magnetic materials.

Findings

Ferromagnetism is eliminated by air annealing and recovered by vacuum annealing.

Magnetic moment correlates with carrier density, indicating carrier-mediated magnetism.

Magnetism is unlikely due to magnetic impurities, confirmed by spectroscopy analyses.

Abstract

The search for oxide-based room-temperature ferromagnetism has been one of the holy grails in condensed matter physics. Room-temperature ferromagnetism observed in Nb-doped SrTiO3 single crystals is reported in this Rapid Communication. The ferromagnetism can be eliminated by air annealing (making the samples predominantly diamagnetic) and can be recovered by subsequent vacuum annealing. The temperature dependence of magnetic moment resembles the temperature dependence of carrier density, indicating that the magnetism is closely related to the free carriers. Our results suggest that the ferromagnetism is induced by oxygen vacancies. In addition, hysteretic magnetoresistance was observed for magnetic field parallel to current, indicating that the magnetic moments are in the plane of the samples. The x-ray photoemission spectroscopy, the static time-of-flight and the dynamic secondary ion mass spectroscopy and proton induced x-ray emission measurements were performed to examine magnetic impurities, showing that the observed ferromagnetism is unlikely due to any magnetic contaminant.