Effect of Nonmagnetic Cap Layers for Nd–Fe–B Thin Films With Small Addition of Rare-Earth Element

Abstract

Nd-Fe-B sintered magnets [1] exhibit a highest maximum energy products (BH) max among all permanent magnets, so they have been used for wide variety of applications. Particularly, their usage to traction motors for hybrid and electric vehicles (HEV's) have been increased recently and also will be increased in the future due to the consideration for the environmental issues. Since the Nd-Fe-B sintered magnets show a relatively low curie temperature of 315 0C, the substitution of heavy rare earth elements (HRE) such as Dy and Tb for Nd is essential for realizing a high thermal stability [2]. However, due to the scarce and localized natural resources of the HRE elements, Dy-free or less permanent magnet is strongly required. It is well known that the structure and the chemistry of the grain boundary phase between Nd 2 Fe 14 B phases play an important role to understand coercivity mechanism. Recent studies revealed that the magnetic coupling between the Nd 2 Fe 14 B main phases is thought to reduce by the grain boundary phase with Nd-rich and Cu-rich alloy phases after post-sinter annealing [3-4]. Furthermore, a lot of studies using a thin film fabrication technique have been done to control a structure and chemistry of the grain boundary phase [5]. However, coercivity mechanism has not yet been understood completely. Then, the elucidation of the coercivity mechanism is essential for reducing the amount of heavy rare earth elements from the Nd-Fe-B magnets. In this study, in order to see the effect of non-magnetic cap layers for Nd-Fe-B thin films, Nd-Fe-B/ Nd-Cu multilayer thin films with small addition of rare earth element have been prepared and their structure and magnetic properties have been investigated.