Nanostructure and hard magnetic properties of exchange coupled Nd-Fe-B/FeCo multilayer films

Abstract

The nanocomposite Nd-Fe-B/FeCo mutilayer films have been prepared by rf sputtering. XRD results and HRTEM observation showed that as-deposited films deposited at substrate temperature of 300K were amorphous. The columnar grains of Nd2Fe14B phase with the c-axis perpendicular to the film plane developed after annealing at 923 K for 15 min. Nd2Fe14B grain size was about 10 nm in average and Nd-O particles of about 7 nm were dispersed within the grains and along the grain boundaries. The magnetization of these samples is found to increase with increasing FeCo layer thickness (tFeCo) and the coercivity decreases with increasing tFeCo. The multilayer films of maximum energy product is 200 kJ/m3 for tFeCo=5 nm at room temperature. The enhancement of the remanence and energy product in nanocomposite films is attributed to the exchange coupling between the magnetically hard and soft phases.