Investigation of ferromagnetic properties of LSMO nanolayers by laser modulated reflectance probe

Abstract

Modulated optical reflectance (MOR) technique is implemented for structural analysis and defectoscopy of thin layers of La 2/3 Sr 1/3 MnO 3 (LSMO). The variation of optical reflectance of the scanned sample surface subjected to periodic photothermal modulation is based on Drude effect. A combination of a pump laser diode and a probe HE-Ne laser in a dual wavelength setup provides an electrical signal proportional to the modulated reflectance at each point of the sample. The detected beam is filtered and modulated selectively by reflection without interference by the substrate properties, the probe beam or external fields. The laser beams are precisely aligned in the focal spot on the sample determining spatial resolution of 10 µm. It is shown that MOR signal at certain conditions around the temperatures of phase transition is proportional to the variations of the charge carrier density and the thermal derivative of magnetoresistance. The described contactless measurement technique may find application in a range of investigations that play important role for realization of new magnetoresistive memories and sensors.