Abstract
The peculiar field-dependent magnetism of has been investigated through an analysis of its dc and ac spin susceptibilities. To account for the easily activated narrow gap of the crystal field for Co in the cobalt oxide layer, the spin-state transition of () between the low-spin (LS) state of and the intermediate-spin (IS) state of is thus seen as thermally activated and exhibits a Boltzmann distribution. The IS state of within each hexagonal superlattice formed by the state of the ions appears randomly within each supercell and shows significant temperature and field dependence. The magnetic field is found to assist in pinning down the thermally activated state of and swings the Boltzmann distribution weight toward a higher fraction of the IS state. The field dependence of the in-plane magnetic moment from the added number of spins is used to explain the origin of -type antiferromagnetic (AF) ordering, particularly that the ferromagnetic (FM)-like behavior below at low field is actually a ferrimagnetic IS spin ordering of .
- Received 3 December 2015
- Revised 12 March 2016
DOI:https://doi.org/10.1103/PhysRevB.93.140402
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