Magnetic compensation at two different composition ratios in rare-earth-free Mn4−xCoxN ferrimagnetic films

Abstract

Ferrimagnets in the vicinity of the magnetic compensation point are of particular interest for spin-torque-based spintronics applications, because they require lower switching currents and thus smaller switching energies. Room-temperature compensation is rather uncommon, but can be obtained by tuning the chemical concentrations of compounds such as ${\mathrm{Co}}_{0.79}{\mathrm{Tb}}_{0.21}$ or ${\mathrm{Co}}_{0.56}{\mathrm{Gd}}_{0.44}$, in order to find the single concentration at which one sublattice compensates the other. Here we study the ferrimagnetic ${\mathrm{Mn}}_{4\text{\ensuremath{-}}x}{\mathrm{Co}}_{x}\mathrm{N}$ films, showing that they presumably possess at room temperature not only one but two different Co concentrations at which the magnetic compensation occurs. Using x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we show that this startling behavior can be explained by the existence of two nonequivalent sites for the Co, when it is inserted in the antiperovskite structure of epitaxial ${\mathrm{Mn}}_{4\text{\ensuremath{-}}x}{\mathrm{Co}}_{x}\mathrm{N}$ films.