MnBi thin films for high temperature permanent magnet applications

Thin films of ferromagnetic LTP-MnBi (Low Temperature Phase of MnBi) have been grown by magnetron sputtering onto quartz substrates. Two particular issues related to LTP-MnBi have been investigated: the strong influence of the growth temperature and the degradation of magnetic properties in time. The temperature dependence on the magnetic, morphological and microstructural properties has been investigated, evidencing drastic changes on the properties of MnBi with small temperature variations. By inducing a gradient of temperature during the growth, two well differentiated regions with different morphology and crystal structure have been observed in a MnBi film sample. On the other hand, aging experiments performed in a different LTP-MnBi sample has led to a notable decrease of 54% in the saturation magnetization after 6 days and a complete loss of ferromagnetic response after 4 months.