Ferrimagnets have received renewed attention as a promising platform for spintronic applications. Of particular interest is the Mn4N from the ${ \epsilon}$-phase of the manganese nitride as an emergent rare-earth-free spintronic material due to its perpendicular magnetic anisotropy, small saturation magnetization, high thermal stability, and large domain wall velocity. We have achieved high-quality (001)-ordered Mn$_{ 4}$N thin film by sputtering Mn onto ${ \eta}$-phase Mn$_{ 3}$N$_{ 2}$ seed layers on Si substrates. As the deposited Mn thickness varies, nitrogen ion migration across the Mn$_{ 3}$N$_{ 2}$/Mn layers leads to a continuous evolution of the layers to Mn$_{ 3}$N$_{ 2}$/Mn$_{ 2}$N/Mn$_{ 4}$N, Mn$_{ 2}$N/Mn$_{ 4}$N, and eventually Mn$_{ 4}$N alone. The ferrimagnetic Mn$_{ 4}$N indeed exhibits perpendicular magnetic anisotropy, and forms via a nucleation-and-growth mechanism. The nitrogen ion migration is also manifested in a significant exchange bias, up to 0.3 T at 5 K, due to the interactions between ferrimagnetic Mn$_{ 4}$N and antiferromagnetic Mn$_{ 3}$N$_{ 2}$ and Mn$_{ 2}$N. These results demonstrate a promising all-nitride magneto-ionic platform with remarkable tunability for device applications.
Categories: cond-mat.mtrl-sci cond-mat.mes-hall
