Radio-frequency echoes from nickel powder

Abstract

Echoes, following a two-pulse rf excitation, were observed in Ni powder. The frequency and temperature ranges were 20–100 MHz and 4.2–300°K, respectively. The echoes are due to mechanical oscillations of the particles excited by magnetostrictive coupling. The relaxation time of the echoes depends strongly on the external magnetic field and history of the sample; it arises from losses due to microeddy currents inside the individual particles.