Investigation of spin moment in Ga-substituted cobalt ferrite: magnetic Compton scattering and photoemission studies

We have studied the spin-dependent electron momentum density distribution in CoGa _x Fe_2−x O₄ (x = 0.2, 0.3) at a low temperature (8 K) using magnetic Compton scattering technique. Further, the effect of Ga doping on the electronic structure is studied using X-ray photoemission spectroscopy (XPS). It is revealed that doping of Ga substitutes the Fe ions predominantly at tetrahedral (P) site, which promotes a gradual immigration of small amount of Co ions from tetrahedral to octahedral (Q) site. Total spin moment increases remarkably on increasing the doping concentration of nonmagnetic Ga (x = 0 → 0.3) in the base cobalt ferrite. It is seen that major contribution to total spin moment mainly arises from Co ions while itinerant electrons show negative polarization. On Ga doping, spin moment at Fe site increases dramatically with a minor increment at Co site. The increased spin moment is attributed to the increased Q/P occupancy ratio of Fe³⁺ as well as Co²⁺ ions as determined using XPS measurements. In contrast, orbital moment does not show such deviations, suggesting that a small amount of Ga doping can enhance the magnetization significantly, without inducing any significant distortion to modify the spin–orbit coupling.