Magnetism of novel rare-earth-free intermetallic compounds

Authors

Haohan Wang, University of Nebraska - LincolnFollow

First Advisor

Xiaoshan Xu

Date of this Version

6-2022

Citation

Wang, Haohan, "Magnetism of novel rare-earth-free intermetallic compounds" (2022).

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Physics and Astronomy, Under the Supervision of Professor Xiaoshan Xu. Lincoln, Nebraska: June, 2022

Copyright © 2022 Haohan Wang

Abstract

Rare-earth-free magnets have drawn lots of interest because of their low cost, and the production is not limited by the shortage of rare-earth elements. This dissertation focuses on three rare-earth-free materials, Fe-Co-Ti alloys, Fe-Ni-B alloys, and Co-Si. All of them are synthesized by arc melting followed by melt-spinning. Fe_3+xCo_3−xTi₂ (x = 0, 2, 3) alloys exhibit hexagonal crystal structures and show non-collinear spin structures according to neutron diffraction. The magnetic moments have projections on both the c-axis and basal plane, and the corresponding misalignment angle exhibits a nonlinear decrease with x, which we explain as a micromagnetic effect caused by Fe-Co site disorder. To increase the magnetic anisotropy of Fe₂Ni alloy, we dope boron into Fe₂Ni and analyze the structure with X-ray diffraction, which shows face center cubic or body center cubic structure according to different temperatures. Magnetic analysis with magnetometer shows that the presence of boron dramatically increases the anisotropy of Fe-Ni-B alloy. Neutron powder diffraction is employed to investigate the magnetism and spin structure in single-phase B20 Co_1.043Si_0.957. The magnetic contributions to the neutron powder diffraction data measured in zero fields are consistent with the helical order among the allowed spin structures derived from group theory. The magnitude of the magnetic moment is larger than the bulk magnetization determined from magnetometry, indicating the formation of a helical spin phase and the associated conical states in high magnetic fields.

Advisor: Xiaoshan Xu