  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.

Materials Science