Spin reorientation induced anisotropic magnetoresistance switching in LaCo0.5Ni0.5O3−δ thin films

Realization of diverse functionalities by tuning magnetic interactions in rare-earth perovskite oxide thin films opens up exciting technological prospects. Strain-induced tuning of magnetic interactions in rare-earth cobaltates and nickelates is of central importance due to their versatility in electronic transport properties. Here we report the spin reorientation induced switching of anisotropic magnetoresistance (AMR) and its tunability with strain in epitaxial ${\mathrm{LaCo}}_{0.5}{\mathrm{Ni}}_{0.5}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin films across the ferromagnetic transition. Moreover, with strain tuning, we observe a twofold to fourfold symmetry crossover in AMR across the magnetic transition temperature. The magnetization measurements reveal a ferromagnetic transition around 50 K. At temperatures below this transition, there is a subtle change in the magnetization dynamics, which reduces the ferromagnetic long-range ordering in the system. X-ray absorption and x-ray magnetic circular dichroism spectroscopy measurements at the Co and Ni $L$ edges reveal a Co spin state transition below 50 K, leading to the AMR switching and also the presence of ${\mathrm{Ni}}^{2+}$ and ${\mathrm{Co}}^{4+}$ ions evidencing the charge transfer from Ni to Co ions. Our work demonstrates the tunability of magnetic interactions mediated electronic transport in cobaltate-nickelate thin films, which is relevant in understanding Ni-Co interactions in oxides for their technological applications such as in AMR sensors.