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MMM 2022

November 07, 2022

Minneapolis, United States

Development of rare earth thick

We have fabricated isotropic Pr-Fe-B thick-film magnets with the thickness of 0.25 mm on a stainless shaft using a PLD (Pulsed Laser Deposition) method and applied them to an ultra-stepping motors with the diameter of less than 3 mm by taking advantage of Pr2Fe14B phase with a large anisotropic magnetic field at room temperature 1. In this study, we focused on the fact that the linear expansion coefficient of Nd element (9.6×10-6 1/K ) is closer to that of stainless steel(10~11×10-6 1/K) than that of Pr element( 6.7×10-6 1/K ). Moreover, evaluation on the temperature dependence of magnetic properties and observation in the mechanical characteristic of Nd-Fe-B thick-film magnets on a stainless substrate (shaft) were carried out.
Figure 1 shows the temperature dependence of the energy product at the operating point of (Nd or Pr)-Fe-B thick-film magnets fabricated on stainless substrates. At 125 °C, the energy product of a Nd-Fe-B thick-film exceeds those of a Pr-Fe-B one and a Nd-Fe-B bond magnet. The result is considered to be attributed to the different temperature dependence of each anisotropic magnetic field for Pr2Fe14B and Nd2Fe14B phases. We also observed the mechanical characteristic of the both films on a stainless substrate and shaft. Several as-deposited Pr-Fe-B film magnets with the Pr contents exceeding 15 at % on the substrate showed exfoliation phenomenon. On the other hand, as-deposited and annealed Nd-Fe-B films (Nd contents : 14 ~ 18 at. %) on the substrate didn’t show mechanical destruction. Although almost all the films showed good adhesion on the stainless shafts as displayed in Fig. 2, one Pr-Fe-B thick-film magnet had a slight crack at the boundary of the shaft and the film. Consequently, enhancement in coercivity of Nd-Fe-B thick-film using an additive at room temperature is a promising method to propose an alternative material of a previously reported Pr-Fe-B thick-film.
1 M. Nakano et.al., IEEE Trans. Magn. Vol. 56, 7516303(2020).

Fig 1 Energy product (Pc =1.0) of (Nd or Pr)-Fe-B thick film magnets as a function of operating temperature.

Fig. 2 Exfoliation phenomenon of as-deposited (Nd or Pr)-Fe-B thick-films on stainless shafts.

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+1Seung-Heon Lee
Seung-Heon Lee and 3 other authors

07 November 2022

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