Magnetic properties and electronic state of MoxFe3−xO4 ferrites

To study effects of strong spin-orbit interaction of Mo ions on magnetic properties, we fabricate ferromagnetic thin films of MoxFe3−xO4 spinel ferrite by sputtering method and measure magnetization MS and magnetic anisotropy (MA). Results show that MS decreases almost linearly with x indicating that Mo ions are in low-spin state, and that the effective uniaxial MA constant changes sign with x. To clarify the electronic and magnetic states of Mo ions, first-principle calculations are performed. The calculated results of MS at low Mo concentrations are consistent with experimental ones, however, they show also existence of local moments on Mo ions. These results are reconciled by considering that the Mo local moments are canceled by a change in the spin polarization around Mo ions.