Electron Theory on Grain-Boundary Structures and Local Magnetic Properties of Neodymium Magnets

Abstract

A fundamental understanding of microstructures is indispensable in improving neodymium-magnets performance at high temperatures. Thus, it is of significant importance to clarify atomic structures and local magnetic properties of interphase interfaces in microstructures, based on electron theory. We studied interfaces between the main phase of neodymium magnets, Nd₂Fe₁₄B, and a subphase NdO_x using massively parallel first-principles electronic-structure calculations with the K computer. As well as the known Cu-addition effect on wettability improvement in metallic Nd subphase, we recognized that some of the added Cu atoms at the (001) interface improve the local magnetic anisotropy of Nd at the interface. Furthermore, we found that the substitution of Fe in the (001)-surface of main-phase grains with Zn can also improve the stability of magnetic anisotropy.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 26–31. In order to more precisely explain the background, the methods, and the results, some parts of the contents were revised. The unit of the energy used in Figs. 2, 3, 4, 5, 7, and 8 was changed, and the Refs. 14) and 23) were added.

Fig. 6 The difference in the electron-density distribution between the Cu-added Nd₂Fe₁₄B bulk single crystal and the pristine one for the region close to the (001) plane including Nd, Fe, and B. Only the positive change is shown for clarity. Due to the open-core pseudopotential used in the first-principles calculations, the distribution of 4f electrons is not included in the figure.