High coercive LTP-MnBi for high temperature applications: From isolated particles to film-like structures

Ferromagnetic low-temperature phase (LTP) of manganese bismuth Mn50Bi50 (at.%) alloy has been prepared by DC magnetron sputtering onto glass by alternative deposition of Bi and Mn with in-situ annealing. Modifying the temperature during deposition and/or during post-growth annealing leads to different microstructures ranging from quasi-isotropic isolated MnBi micro-particles to larger platelet-like individual ones up to highly coalesced textured film-like areas. These microstructural variations determine the magnetic behaviour, including change in the easy axis direction and possibility of varying coercivity from 4 to 16 kOe at room temperature. In all the cases, coercivity has a positive temperature coefficient, reaching 29 kOe at 500 K, being among the largest reported coercivity for MnBi. Isolated LTP-MnBi microstructures, being homogeneously distributed onto glass, have been grown while avoiding the presence of unreacted Bi regions between the MnBi structures. The possibility of tuning microstructural and magnetic properties, in combination with their time stability, makes them interesting candidates for high temperature permanent magnet applications. [Display omitted] •Variety of LTP-MnBi structures from isolated micro-particles to film-like ones.•Different microstructure determines strong variation of the magnetic behaviour.•Maximum BHmax of 14 MGOe.•Maximum coercivity of 29 kOe at 500 K, among the largest reported ones for MnBi.•Truly isolated MnBi particles differing from MnBi separated by unreacted Bi.