THE NON-MARTENSITIC DIFFUSIONLESS TRANSITION IN MANGANESE ARSENIDE AT ABOUT 40 °C

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Abstract
We have investigated the nature of the transition at about 40 °C in manganese arsenide. It is already well known that the transition involves a discontinuous change of the length of the a axis of the hexagonal unit cell, and that there is no change of crystal structure. The transition is accompanied by a loss of ferromagnetism of MnAs on proceeding to higher temperature. We find that the transformation takes place by a novel diffusionless non-martensitic mechanism. It appears that plastic deformation of MnAs is impossible and so, instead of the change following the martensitic pattern, the strain energy of the transformation is minimized by a fragmentation of the crystal grains into pencil-like subgrains whose direction lies parallel to the c axis of the crystals.