Co-occurrence of Superparamagnetism and Anomalous Hall Effect in Highly Reduced Cobalt Doped Rutile TiO2 Films

TL;DR

This study investigates the coexistence of superparamagnetism and anomalous Hall effect in highly reduced cobalt-doped TiO2 films, revealing nano-sized cobalt clusters and challenging the interpretation of AHE as an intrinsic ferromagnetism indicator.

Contribution

It provides detailed magnetic and structural analysis showing nano-sized cobalt clusters co-occurring with AHE in doped TiO2 films, questioning previous assumptions about AHE's origin.

Findings

Presence of 8-10 nm cobalt clusters at interfaces

Co-occurrence of superparamagnetism and AHE

Challenges intrinsic ferromagnetism interpretation

Abstract

We report a detailed magnetic and structural analysis of highly reduced Co doped rutile TiO2 films displaying an anomalous Hall effect (AHE). The temperature and field dependence of magnetization, and transmission electron microscopy clearly establish the presence of nano-sized superparamagnetic cobalt clusters of 8-10 nm size in the films at the interface. The co-occurrence of superparamagnetism and AHE raises questions regarding the use of the AHE as a test of the intrinsic nature of ferromagnetism in diluted magnetic semiconductors.