Annealing Effect on Acoustic Property of Fe/Pt Superlattice Studied by Picosecond Ultrasound

Abstract

Fe/Pt superlattices deposited on glass substrates were annealed after deposition, and the relationships among annealing temperature, out-of-plane longitudinal-wave elastic constant, and the attenuation of a GHz longitudinal acoustic pulse propagating in the superlattices were studied using picosecond ultrasound. Picosecond ultrasound generates and detects GHz longitudinal acoustic pulses using ultrashort pulse lights, and is capable of evaluating the acoustic property of a superlattice thinner than 100 nm without touching the specimen. The elastic constant of an as-deposited superlattice was smaller than those of bulk Fe and Pt; it increased as annealing temperature increased. The attenuation also increased as annealing temperature increased. The frequency dependence of the attenuation indicated the formation of FePt alloy at interfaces at 300 °C. Thus, we confirmed that the investigation of acoustic properties using picosecond ultrasound can be a powerful tool for evaluating the structural evolution in superlattices.