Origin of ferromagnetism in (Zn,Co)O from magnetization and spin-dependent magnetoresistance
T. Dietl, T. Andrearczyk, A. Lipi\'nska, M. Kiecana, Maureen Tay and, Yihong Wu
TL;DR
This paper investigates the origin of ferromagnetism in (Zn,Co)O, combining experimental and theoretical approaches to reveal that surface spins of antiferromagnetic nanocrystals cause the observed magnetic properties and anisotropy.
Contribution
It provides a new model attributing ferromagnetism in (Zn,Co)O to surface spins of Co-rich nanocrystals, supported by structural and magnetic analysis.
Findings
Spontaneous magnetization linked to uncompensated surface spins.
Large anisotropy explained by Co ions' spin Hamiltonian.
Magnetoresistance influenced by spin-dependent localization effects.
Abstract
In order to elucidate the nature of ferromagnetic signatures observed in (Zn,Co)O we have examined experimentally and theoretically magnetic properties and spin-dependent quantum localization effects that control low-temperature magnetoresistance. Our findings, together with a through structural characterization, substantiate the model assigning spontaneous magnetization of (Zn,Co)O to uncompensated spins at the surface of antiferromagnetic nanocrystal of Co-rich wurtzite (Zn,Co)O. The model explains a large anisotropy observed in both magnetization and magnetoresistance in terms of spin hamiltonian of Co ions in the crystal field of the wurtzite lattice.
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