Enhanced exchange bias in MnN/CoFe bilayers after high-temperature annealing

TL;DR

This study demonstrates that high-temperature annealing significantly enhances exchange bias in MnN/CoFe bilayers, achieving over 2700 Oe at room temperature, with the effect linked to nitrogen diffusion and optimized annealing conditions.

Contribution

It reveals the impact of high-temperature annealing on exchange bias enhancement in MnN/CoFe bilayers, highlighting the role of nitrogen diffusion and specific thickness and temperature conditions.

Findings

Exchange bias exceeds 2700 Oe at room temperature after annealing.

Maximum exchange bias over 2000 Oe achieved for 42-48 nm MnN thickness.

Nitrogen diffusion into Ta buffer correlates with increased exchange bias.

Abstract

We report an exchange bias of more than $2700\,$Oe at room temperature in MnN/CoFe bilayers after high-temperature annealing. We studied the dependence of exchange bias on the annealing temperature for different MnN thicknesses in detail and found that samples with $t_{\text{MnN}}>32\,$nm show an increase of exchange bias for annealing temperatures higher than $T_{\text{A}}=400\,^{\circ}$C. Maximum exchange bias values exceeding $2000\,$Oe with reasonably small coercive fields around $600\,$Oe are achieved for $t_{\text{MnN}}= 42, 48\,$nm. The median blocking temperature of those systems is determined to be $180\,^{\circ}$C after initial annealing at $T_{\text{A}}=525\,^{\circ}$C. X-ray diffraction measurements and Auger depth profiling show that the large increase of exchange bias after high-temperature annealing is accompanied by strong nitrogen diffusion into the Ta buffer layer of the stacks.