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

TL;DR

This paper introduces a polycrystalline MnN/CoFe bilayer system exhibiting record-high room temperature exchange bias, with tunable thermal stability, good oxidation resistance, and practical microstructure integration.

Contribution

It reports a new MnN/CoFe exchange bias system with unprecedented room temperature bias and simple fabrication process.

Findings

Exchange bias up to 1800 Oe at room temperature

Thermal stability tunable via nitrogen content

Good oxidation stability and microstructure compatibility

Abstract

We report on the new polycrystalline exchange bias system MnN/CoFe, which shows exchange bias of up to 1800Oe at room temperature with a coercive field around 600Oe. The room temperature values of the interfacial exchange energy and the effective uniaxial anisotropy are estimated to be $J_\mathrm{eff} = 0.41\,\mathrm{mJ}/\mathrm{m}^2$ and $K_\mathrm{eff} = 37\,\mathrm{kJ}\,/\,\mathrm{m}^3$. The thermal stability was found to be tunable by controlling the nitrogen content of the MnN. The maximum blocking temperature exceeds $325^\circ$C, however the median blocking temperature in the limit of thick MnN is $160^\circ$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 GMR 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.