Determination of the magnetization scaling exponent for single crystal La$_{0.8}$Sr$_{0.2}$MnO$_3$ by broadband microwave surface impedance measurements

TL;DR

This study uses broadband microwave surface impedance measurements to accurately determine the critical magnetization scaling exponent in single crystal La$_{0.8}$Sr$_{0.2}$MnO$_3$, confirming mean-field theory predictions near the Curie temperature.

Contribution

The paper introduces a broadband microwave reflection method to measure spontaneous magnetization and critical exponents without external magnetic fields, providing more definitive results.

Findings

Curie temperature T_C=305.5 K

Scaling exponent β=0.45

Results agree with mean-field theory

Abstract

Employing a broadband microwave reflection configuration, we have measured the complex surface impedance, $Z_S(\omega,T)$, of single crystal La$_{0.8}$Sr$_{0.2}$MnO$_3$, as a function of frequency (0.045-45 GHz) and temperature (250-325 K). Through the dependence of the microwave surface impedance on the magnetic permeability, $\hat\mu(\omega,T)$, we have studied the local magnetic behavior of this material, and have extracted the spontaneous magnetization, $M_0(T)$, in {\em zero applied field}. The broadband nature of these measurements and the fact that no external field is applied to the material provide a unique opportunity to analyze the critical behavior of the spontaneous magnetization at temperatures very close to the ferromagnetic phase transition. We find a Curie temperature $T_C=305.5\pm 0.5$ K and scaling exponent $\beta=0.45\pm 0.05$, in agreement with the prediction of mean-field theory. We also discuss other recent determinations of the magnetization critical exponent in this and similar materials and show why our results are more definitive.