We study the spin Hall magnetoresistance (SMR) in Pt grown in situ on CoFe2O4 (CFO) ferrimagnetic insulating (FMI) films. A careful analysis of the angle-dependent and field-dependent longitudinal magnetoresistance indicates that the SMR contains a contribution that does not follow the bulk magnetization of CFO but it is a fingerprint of the complex magnetism at the surface of the CFO layer, thus signaling SMR as a tool for mapping surface magnetization. A systematic study of the SMR for different temperatures and CFO thicknesses gives us information impossible to obtain with any standard magnetometry technique. On one hand, surface magnetization behaves independently of the CFO thickness and does not saturate up to high fields, evidencing that the surface has its own anisotropy. On the other hand, characteristic zero-field magnetization steps are not present at the surface while they are relevant in the bulk, strongly suggesting that antiphase boundaries are the responsible of such intriguing features. In addition, a contribution from ordinary magnetoresistance of Pt is identified, which is only distinguishable due to the low resistivity of the in-situ grown Pt.
@article{arxiv.1510.01449,
title = {Spin Hall magnetoresistance as a probe for surface magnetization in Pt/CoFe$_2$O$_4$ bilayers},
author = {Miren Isasa and Saül Vélez and Edurne Sagasta and Amilcar Bedoya-Pinto and Nico Dix and Florencio Sánchez and Luis E. Hueso and Josep Fontcuberta and Fèlix Casanova},
journal= {arXiv preprint arXiv:1510.01449},
year = {2016}
}