Abstract
Low temperature phase MnBi compound was prepared by annealing the melt-spun amorphous MnBi ribbons. Temperature dependences of structure, magnetization and coercivity were investigated using neutron/X-ray powder diffraction and magnetic measurements. It is found that the lattice parameter c/a ratio of the MnBi increases with the increasing temperature and finally reaches a maximum of 1.433 around 600K. No structural phase transition is observed at 633K. Especially, the lattice constants of MnBi at 700K are a=b=4.30919Å, and c=6.17521Å, which are not in accordance with the previous data for bulk MnBi. Magnetic moment of Mn atom tends to lie in the ab-plane at 10K, and turns to align along c-axis around 90K. The growth of LTP MnBi grains is observed above 500K, which increases the content of MnBi. The coercivity of MnBi shows a positive temperature coefficient, reaches a maximum of 2.5T at 540K, and decreases to 1.8T at 610K. The temperature dependence of the coercivity is related to the change of magnetocrystalline anisotropy, and shows strong dependence on the sizes of MnBi particles.
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