Magnetism of novel rare-earth-free intermetallic compounds

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. Fe3+xCo3−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 Co1.043Si0.957. 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 X