Electron-Spin Resonance of a La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Slab

Abstract

We have studied electron-spin resonance (ESR) spectra of a La0.7Sr0.3MnO3 slab. Experimental results reveal that ESR spectra in the ferromagnetic (FM) region are followed with a broadly resonant mode as θ = 90°, but several modes as θ = 0°. Their spectral parameters depend strongly on θ. When keeping θ = 0° and measuring the temperature dependence of ESR spectra, it is found that several resonant modes in the FM region become a single mode in the Dysonian line-shape at temperatures T >; Tmin ≈ 1.1 TC. At Tmin, the spectral linewidth reaches to a minimum value of ΔHmin= 283 Oe. Temperature dependences of the EPR intensity above Tmin obey a function I(T) = Io exp(Ea/ kB T). Having based on the relation of I(T) ∝ χ(T) = 1/(T-Θ) , we obtained the Curie-Weiss temperature Θ to be 376 K. If using a simple relation of g = hν/ μB Hr (Hr is the resonant position, and μB is the Bohr magneton), we have found that the effective Lande factor g increases from 1.91 (around Tmin) to ~ 1.98 (at 473 K) close to the value of g = 2.0 for spin-spin interactions of Mn ions. This could be due to the additional presence of magnetic interactions, besides spin-spin interactions, such as interactions between FM clusters and/or spin-orbital coupling. Interestingly, despite the sample in the PM regime, the spectral parameters depend on the angle θ. This is assigned to an anisotropic field related to Mn 3+-Mn 4 + FM clusters persisting above Tmin. At 470 K, the anisotropy constant obtained is Ku ≈ 57 erg/cm 3, much smaller than that in the FM region.