A Mössbauer effect study of 57Fe in transition metal monoborides

Abstract

The phase characteristics and nuclear hyperfine properties of 45 transition metal monoborides M_1−x Fe_x B were studied by Mössbauer effect spectroscopy of ⁵⁷Fe. Transmission measurements with powders were completed in the temperature range 4.2−1000 K; additional scattering and 18 kOe applied field data were collected at 300 K. Measured ⁵⁷ Fe nuclear hyperfine parameters are discussed in terms of atomic bonding, charge transfer, and spontaneous magnetism in the borides. Within the context of the rigid band model, the isomer shift data for all boride phases indicate an electron transfer from boron to the metal 3d band. Similarly, the effective magnetic hyperfine field in ferromagnetic monoborides is proportional to the magnetization and also reveals a possible charge transfer from boron to metal. Quadrupole coupling constant results show a strong ionic contribution to the electric field gradient at the ⁵⁷Fe site in the monoborides. Measurements on FeB confirm the existence of two distinct structural modifications possessing different magnetic hyperfine fields but the same Curie temperatures. The defect (α) phase of FeB appears to be stabilized by the addition of manganese.