Effect of periodicity on the magnetic anisotropy in spinel oxide superlattices

Abstract

Metamaterials, fabricated by assembling different compounds at the nanoscale, can have properties not found in naturally occurring materials, and therefore offer new avenues to develop novel devices. In the realm of spintronics, where the spin of the electrons is used to extend the capabilities of electronic devices, the quest for such new functional materials has expanded towards magnetic oxides. Here, finding methods to control their magnetic anisotropy is crucial to achieve higher memory density and longer stability. In order to address this challenge, we combined two oxides with a spinel crystal structure, synthesizing CoCr 2 O 4 /CoFe 2 O 4 superlattices with layers only few unit cells thick. We show that the superlattices present a reorientation of the magnetic easy axis from in plane to out of plane when warmed up, at a temperature determined by the periodicity. We can describe this with a model that includes the strain-induced anisotropy of the two materials and their different temperature dependence. This approach to create artificial materials, involving engineering superlattices to tailor the magnetic anisotropy, can be generalized to a wide range of compounds that can be grown strained on suitable substrates.