Mechanism of Transition in Magnetite at Low Temperatures

When magnetite is cooled through -160°C it is known to undergo a transition (cubic to orthorhombic) that is influenced by the presence of a magnetic field. Our experiments are in agreement with the following mechanism of the transition: The orthorhombic $c$ axis is parallel to one of the original cubic axes and is the axis of easiest magnetization. Generally, different regions of the original crystal will transform with their $c$ axes lying along different cubic axes, and when no field is applied there are 6 different orientations which different regions assume. When a field is applied during cooling a $c$ axis tends to lie along the original cubic axis that is nearest to the applied field, the $a$ and $b$ axes having less but different tendencies to lie parallel to the field.