Magnetic resonance study of bulk and thin film EuTiO3

TL;DR

This study uses magnetic resonance to analyze EuTiO3 in bulk and thin film forms, revealing details about spin interactions, magnetic anisotropy, and the effects of demagnetization and defects across temperatures.

Contribution

It provides detailed characterization of EuTiO3's magnetic properties in bulk and thin film forms, including spin interactions, anisotropy, and the impact of aging on film structure.

Findings

Spin-spin exchange frequency is 15-15.5 GHz.

Bulk EuTiO3 shows a linewidth minimum at T_N=5.5 K.

Thin film exhibits magnetostatic mode splitting below T_N.

Abstract

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 15-15.5 GHz and the estimated critical exponent of the spin correlation length is ~ 0.5. In the bulk samples, the spectra exhibited a distinct minimum in the linewidth at the N\'eel 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/cm3 or 5.5 mu_B/unit cell at T = 3.5 K.