Study of Structural and Magnetic Properties of Pd-Doped Co₄N Thin Films

Tetra metal nitrides (M₄N; M = Cr, Fe, Co, Mn, Ni) are a promising spintronic material with an anti-perovskite structure and fascinating magnetic characteristics due to a magneto-volume effect. Though a fully stochiometric Mn₄N or Fe₄N has been achieved, the lattice parameter (LP) of Co₄N was always been found to be significantly lower than the anticipated theoretical values, indicating a sub-stochiometric Co₄N phase. The formation enthalpy of Co₄N is slightly positive resulting in unfavorable thermodynamical conditions and significant out-diffusion of N from Co₄N. In this work, we present a comparative study of undoped and Pd-doped Co₄N thin films synthesized using a reactive nitrogen sputtering. The structural, composition, and magnetic properties have been studied by combining x-ray diffraction, Rutherford backscattering, energy-dispersive x-ray spectroscopy, secondary ion mass spectroscopy, vibrating sample magnetometer, magneto-optical Kerr effect, and polarized neutron reflectivity measurements. It was found that Pd doping of about 5 at.% results in a significant enhancement in the LP of Co₄N signifying a higher amount of N retention without adversely affecting the growth and magnetic properties. It is further suggested that the amount of Pd doping may further be increased to realize a fully stoichiometric Co₄N.