Evidence of defect-induced ferromagnetism in ZnFe${}_2$O${}_4$ thin films

X-ray absorption near-edge and grazing incidence X-ray fluorescence spectroscopy are employed to investigate the electronic structure of ZnFe${}_2$O${}_4$ thin films. The spectroscopy techniques are used to determine the non-equilibrium cation site occupancy as a function of depth and oxygen pressure during deposition and its effects on the magnetic properties. It is found that low deposition pressures below 10${}^{-3}$ mbar cause iron superoccupation of tetrahedral sites without Zn${}^{2+}$ inversion, resulting in an ordered magnetic phase with high room temperature magnetic moment.