Emergent magnetic state in (111)-oriented quasi-two-dimensional spinel oxides

Abstract

We report on the emergent magnetic state of (111)-oriented CoCr2O4 ultrathin films sandwiched by Al2O3 in the quantum confined geometry. At the two-dimensional crossover, polarized neutron reflectometry reveals an anomalous enhancement of the total magnetization compared to the bulk value. Synchrotron x-ray magnetic circular dichroism (XMCD) demonstrates the appearance of long-range ferromagnetic ordering of spins on both Co and Cr sublattices. Brillouin function analyses further corroborates that the observed phenomena are due to the strongly altered magnetic frustration, manifested by the onset of a Yafet-Kittel type ordering as the new ground state in the ultrathin limit, which is unattainable in the bulk.

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• Perspective: Strongly correlated and topological states in [111] grown transition metal oxide thin films and heterostructures
• Lattice dynamics and magnetic exchange interactions in GeCo2O4, a spinel with S = 1/2 pyrochlore lattice
• Epitaxial stabilization of (111)-oriented frustrated quantum pyrochlore thin films
• Orientation-dependent stabilization of MgCr${}_2$O${}_4$ spinel thin films
• On the complexity of spinels: Magnetic, electronic, and polar ground states