Ferromagnetic Resonance Study of the Verwey Phase Transition of Magnetite Thin Film on MgGa₂O₄(001) Substrate

We report on temperature-dependent broadband ferromagnetic resonance studies of magnetite (Fe
₃
O
₄
) film of thickness 30 nm grown on magnesium gallate [MgGa
₂
O
₄
(001)] single crystal substrate by pulsed laser deposition. The isotropic point, i.e., the temperature at which magnetocrystalline anisotropy vanishes, is found to be approximately 120 K, which is 10 K lower than the bulk value. The Verwey transition is close to 110 K, again about 10 K lower than the bulk crystal value. Below the Verwey transition temperature, the uniaxial anisotropy of the monoclinic phase increases gradually and asymptotically approaches a constant value indicating a smooth structural transition rather than a sudden change. Resonance linewidth and effective damping increase abruptly below 110 K. The effective damping constant is determined to be ~0.01 and is independent of temperature from 300 K to 120 K.