The alignment, aggregation and magnetization behaviors in MnBi-Bi composites solidified under a high magnetic field

Bi-6 wt% Mn alloy is solidified under a high magnetic field and its microstructures and magnetic properties have been investigated. Microstructure results show that three kinds of morphology of MnBi phase appear in different temperature zones. In all these cases, the grains are orientated with the (001)-crystal direction along the magnetic field direction and aggregated. Magnetic measurement shows a pronounced anisotropy in magnetization in directions normal and parallel to the fabrication field, resulting from this alignment. The effect of the magnetic field on the Mn1.08Bi/MnBi (paramagnetic/ferromagnetic) phase transformation has been studied and the result shows that the phase transformation temperature T-C increases with the increase of the external magnetic field and under a field of 10 T, a typical increase of T-C is 20 degrees C during heating and 22 degrees C during cooling. The change in the morphology and in the magnetic properties of MnBi phase is discussed from the phase transformation and the crystal structure change in magnetic field. (C) 2006 Elsevier Ltd. All rights reserved.