Rare-earth free permanent magnets and permanent magnet synchronous motors
In this dissertation, basic and applied research programs are engaged that range from the fundamental magnetism and magnetic properties of ferro- and ferrimagnetic materials to the design and fabrication of rare earth (RE) free permanent and soft magnetic materials for an interior permanent magnet synchronous motor (IPMSM) (i.e., motor for electric vehicles and plug-in electric vehicles) and heat assisted magnetic recording media (HAMR) with 4 Tb/in2 information storage applications. The applied research program emphasizes the design and synthesis of new RE-free permanent magnetic materials and magnetic exchange coupled core(hard)-shell(soft) particles to achieve a high maximum energy product [(BH)max], and the design of an advanced IPMSM based on RE free permanent magnets. The electronic structures of hard magnetic materials such as Mn-Al, Mn-Bi, Mn-Bi-X, Fe-Pt, Fe-Pt-X, SrFe12O19, and SrFe12O19-X (X = transition elements) and soft magnetic materials such as nanocrystalline and Mn-B were calculated based on the density functional theory (DFT), and their exchange coupled magnetic properties with soft magnets were designed according to the size and shape of the particles. The calculated magnetic and electronic properties were used to obtain the temperature dependence of saturation magnetization Ms(T) and anisotropy constant K(T) within the mean field theory. Thereby, the temperature dependence of the maximum energy product [(BH)max(T)] is calculated using the calculated Ms(T) and K(T). The experimental approaches were based on chemical and ceramic processes to synthesize hard and soft magnetic materials. Prior to synthesis, material design parameters were optimized by first-principles calculations and micromagnetic simulations. Lastly, performance of RE-free MnAl, MnBi, SrFe12O19, and Alnico IPMSMs, designed with the finite element method (FEM), at 23 and 200 oC were evaluated and compared to a RE Nd Fe B IPMSM. The performance parameters include torque, efficiency, and power. It was found that the performance of the MnBi and Alnico IPMSM is comparable with the Nd-Fe-B IPMSM.