Large exchange bias in polycrystalline MnN/CoFe bilayers at room temperature

Abstract

We report on the new polycrystalline exchange bias system MnN/CoFe, which shows exchange bias of up to 1800 Oe at room temperature with a coercive field around 600 Oe. The room-temperature values of the interfacial exchange energy and the effective uniaxial anisotropy are estimated to be ${J}_{\mathrm{eff}}=0.41\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$ and ${K}_{\mathrm{eff}}=37\phantom{\rule{0.28em}{0ex}}\mathrm{kJ}/{\mathrm{m}}^{3}$. The thermal stability was found to be tunable by controlling the nitrogen content of MnN. The maximum blocking temperature exceeds $325{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, however the median blocking temperature in the limit of thick MnN is $160{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Good oxidation stability through self-passivation was observed, enabling the use of MnN in lithographically defined microstructures. As a proof of principle we demonstrate a simple giant magnetoresistance stack exchange biased with MnN, which shows clear separation between parallel and antiparallel magnetic states. These properties come along with a surprisingly simple manufacturing process for the MnN films.