Enhancement of the Energy Product in Soft- and Hard-magnetic

Abstract

For developing rare-earth free permanent magnets, the soft- and hard-magnetic mixtures have been extensively investigated [1,2]. Although the magnetic mixtures have theoretically explicit prospect for rare-earth free permanent magnets with proper energy product [3,4], 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. In order to elucidate the magnetic mixture for 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 simulations according to various ratio of two phases, their microstructures, 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 it distributes normally in each grain 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.