Emergence of Ferromagnetism Through the Metal-Insulator Transition in Undoped Indium Tin Oxide Films

TL;DR

This study demonstrates the emergence of bulk ferromagnetism in undoped indium tin oxide films as they undergo a metal-insulator transition, linked to increased oxygen vacancies and sample granularity, using a novel measurement technique.

Contribution

It reveals how ferromagnetism arises in undoped ITO near the MIT due to oxygen vacancies and granularity, employing a new highly sensitive torque magnetometry method.

Findings

Ferromagnetism appears as resistance approaches the MIT.

Magnetization hysteresis and anomalous Hall effect confirm ferromagnetism.

Sign change of AHE suggests interplay between impurity and conduction bands.

Abstract

We present a detailed study of the emergence of bulk ferromagnetism in low carrier density samples of undoped indium tin oxide (ITO). We used annealing to increase the density of oxygen vacancies and change sample morphology without introducing impurities through the metal insulator transition (MIT). We utilized a novel and highly sensitive "Corbino-disk torque magnetometry" technique to simultaneously measure the thermodynamic and transport effects of magnetism on the same sample after successive annealing. With increased sample granularity, carrier density increased, the sample became more metallic, and ferromagnetism appeared as resistance approached the MIT. Ferromagnetism was observed through the detection of magnetization hysteresis, anomalous Hall effect (AHE), and hysteretic magnetoresistance. A sign change of the AHE as the MIT is approached may elucidate the interplay between the impurity band and the conduction band in the weakly insulating side of the MIT.