Modulated optical reflectance measurements on La2/3Sr1/3MnO3 thin films

TL;DR

This study applies modulated optical reflectance to La2/3Sr1/3MnO3 thin films, revealing how the MOR signal relates to resistivity and charge carrier changes across the ferromagnetic to paramagnetic transition, with potential for device applications.

Contribution

It demonstrates the use of MOR for characterizing LSMO thin films and explores the underlying mechanism linking MOR signals to charge carrier variations.

Findings

MOR signal correlates with resistivity derivative near Curie temperature

MOR technique can detect film homogeneity and magnetic transitions

Charge carrier concentration changes influence MOR signals

Abstract

The modulated optical reflectance (MOR) measurement technique was applied to colossal magnetoresistive materials, in particular, La2/3Sr1/3MnO3 (LSMO) thin films. The contactless measurement scheme is prospective for many applications spanning from materials characterization to new devices like reading heads for magnetically recorded media. A contrasted room temperature surface scan of a 100 microns wide 400 microns long bridge patterned into LSMO film provided preliminary information about the film homogeneity. Then the temperature was varied between 240 and 400 K, i.e. through the ferromagnetic to paramagnetic transition. A clear relation between the MOR signal measured as function of the temperature and the relative derivative of the resistivity up to the Curie temperature was observed. This relationship is fundamental for the MOR technique and its mechanism was explored in the particular case of LSMO. Analysis in the framework of the Drude model showed that, within certain conditions, the measured MOR signal changes are correlated to changes in the charge carrier concentration.