PLD-fabricated Pr-Fe-B thick film magnets applied to small motors

Although a conventional isotropic Nd-Fe-B bonded magnet (coercivity: 800 kA/m, thickness: 350 μm) has been widely used for a miniaturized motor, deposition of a thick film magnet without resin directly on a small shaft enables us to advance the further reduction of the motor. When obtaining the film magnet on the shaft, we carried out fundamental experiments using a stainless plate. Namely, we investigated the mechanical characteristic such as adhesion together with magnetic properties of PLD (Pulsed Laser Deposition)-made films as a function of Pr content. It was found that Pr-Fe-B films with Pr content above 15 at. % tended to peel from the plates after the deposition. We suppose that the result is attributed to the different linear expansion coefficient between a stainless (10.3×10-6 K-1) and Pr element (6.7×10-6 K-1). On the other hand, an increase in Pr contents of the samples enabled us to enhance coercivity compared with that of a conventional Nd-Fe-B bonded magnet. In the study, we prepared a 250 μm-thick Pr-Fe-B film magnet with the coercivity (Hcj) of approximately 1250 kA/m on a thin stainless shaft applicable to a small motor by the PLD.