Micromagnetic analysis of remanence and coercivity of nanocrystalline Pr–Fe–B magnets

Abstract

Nanocrystalline exchange coupled Pr11.76Fe82.36B5.88 single-phase and Pr9Fe85B6 two-phase magnets containing 20 vol % α-Fe were produced using mechanical alloying. Micromagnetic finite element simulations were used to analyze the temperature dependence of the magnetic properties. In the single-phase exchange-coupled magnet a significant enhancement of the remanence Jr=1.1 T was achieved at room temperature. A further enhancement of the remanence was observed in two-phase α-Fe containing magnets reaching a remanence of Jr=1.23 T. The corresponding values of the coercive field are μ0Hc=0.81 T and μ0Hc=0.57 T for the single-phase magnet and the two-phase magnet, respectively. Remanence enhancement becomes more effective with increasing temperature, compensating the decrease of the saturation polarization. In the two-phase magnet the remanence increases from Jr=1.12 to Jr=1.23 T as the temperature is increased from 200 to 300 K. Micromagnetic calculations clearly show that the increase of the exchange length with increasing temperature improves the effective coupling between the Pr2Fe14B and the α-Fe phase. The decrease of the coercive field with increasing temperature has to be attributed to the temperature dependence of the anisotropy field.