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We report on broadband and in-plane angle dependent ferromagnetic resonance measurements of MnN (30 nm)/CoFeB ( t CoFeB ) exchange bias bilayer systems with CoFeB thicknesses ranging from 5 to 20 nm. We find that the strong unidirectional anisotropy in this system is accompanied by a strong uniaxial in-plane anisotropy and a small interfacial perpendicular anisotropy ( K ⊥ , i = 0.043 ± 0.001 erg / cm 2 ). The strength of the interfacial exchange bias coupling in this system Δ σ eb = 0.193 ± 0.005 erg / cm 2 is only 2.5 times larger than the interfacial uniaxial coupling strength Δ σ u = 0.076 ± 0.003 erg / cm 2 . The relaxation in this system also shows a strong unidirectional and uniaxial in-plane anisotropy. While the observed thickness dependence of the uniaxial anisotropy of the relaxation is consistent with an interfacial two-magnon scattering contribution, we find that this is not the case for the unidirectional relaxation.

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.

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., 7 pages, 6 figures