Magnetic compensation in sputtered ferrimagnetic Mn_4-xGa_xN thin films

Fully compensated ferrimagnets are attracting increasing attention for spintronics. Here we report a series of Mn_4-xGa_xN ferrimagnetic thin films grown on (100)-oriented MgO by magnetron sputtering. A small tetragonal distortion with c/a = 0.99 leads to perpendicular magnetic anisotropy with a [001] easy axis. The magnetisation decreases with increasing Ga content up to x = 0.18, where the magnetic moment is close to zero at room temperature. It increases with further increase of x, indicating the magnetic compensation composition has been crossed and the dominant sublattice has switched from Mn on the corner sites, where it is progressively replaced by nonmagnetic Ga, to noncollinear Mn on the face-centered sites. Compensation found at 235 K in a remanent scan of the x = 0.18 film is confirmed by measurements of the anomalous Hall effect and interpolation of the inverse coercivity. This work establishes the conditions for thin film growth of Mn_4-xGa_xN that could be used for room-temperature ferrimagnetic spintronics. The behaviour of thin films is compared with that of bulk material.