Determination of the magnetization scaling exponent for single-crystal La0.8Sr0.2MnO3 by broadband microwave surface impedance measurements

Employing a broadband microwave reflection configuration, we have measured the complex surface impedance, ZS(v ,T), of single-crystal La0.8Sr0.2MnO3, 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, m̂(v ,T), we have studied the local magnetic behavior of this material, and have extracted the spontaneous magnetization, M 0(T), in 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 TC5305.560.5 K and scaling exponent b50.4560.05, 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.