Magnetic resonance study of bulk and thin film EuTiO₃

Magnetic resonance spectra of EuTiO₃ in both bulk and thin film form were taken at temperatures from 3-350 K and microwave frequencies from 9.2-9.8 and 34 GHz. In the paramagnetic phase, magnetic resonance spectra are determined by magnetic dipole and exchange interactions between Eu²⁺ spins. In the film, a large contribution arises from the demagnetization field. From detailed analysis of the linewidth and its temperature dependence, the parameters of spin-spin interactions were determined: the exchange frequency is 10.5 GHz and the estimated critical exponent of the spin correlation length is  ≈0.4. In the bulk samples, the spectra exhibited a distinct minimum in the linewidth at the Néel temperature, T _N  ≈  5.5 K, while the resonance field practically does not change even on cooling below T _N. This is indicative of a small magnetic anisotropy ~320 G in the antiferromagnetic phase. In the film, the magnetic resonance spectrum is split below T _N into several components due to excitation of the magnetostatic modes, corresponding to a non-uniform precession of magnetization. Moreover, the film was observed to degrade over two years. This was manifested by an increase of defects and a change in the domain structure. The saturated magnetization in the film, estimated from the magnetic resonance spectrum, was about 900 emu cm^-3 or 5.5 µ _B/unit cell at T  =  3.5 K.