Energy Product Enhancement in Soft-and Hard-magnetic Mixtures

Abstract

The soft- and hard-magnetic mixtures have been extensively investigated for developing rare-earth free magnet. Even though the magnetic mixtures have theoretically explicit prospect for rare-earth free permanent magnets with high energy product, no significant improvement has not been found yet because of their complicated dependence on the microstructure such as a grain size, shape, anisotropy distribution, exchange coupling among grains, and different phases. To elucidate the magnetic mixture is substantially valuable as rare-earth free permanent magnets, it is necessary to develop a clear model in which various microstructural elements are considered. In this works, we studied the magnetic mixtures composed of MnBi (hard), and FeCo (soft) by micromagnetic methods according to various ratio of two phases, their microstructures including grains, and their couplings. As a model system, we adopt the 160×160×40 nm3 sized rectangular prism in which MnBi and FeCo phases are formed in different grains as shown in Fig. 1(a). We assumed that the easy axis of magneto-crystalline anisotropy is z-axis and the easy axis of each grains follows Gaussian distribution with standard deviation of 0.03. To estimate energy product, the hysteresis loops were calculated by applying external magnetic field ranging from -5 T to 5 T along z-axis and B- and H-fields were obtained directly from them. As shown in Fig. 1 (b), the energy product varies dramatically according to the ratio of mixture. In the presentation, we will discuss about the energy product enhancement by modulating the microstructures and the ratio of soft- and hard-magnets in mixtures.