Crystal Axis Switching Effects in the Thermal Expansion and Magnetostriction of Magnetite

Abstract

The twinned state of natural magnetic below the Verwey transition was studied by measurements of the thermal expansion and longitudinal magnetostriction with a three-terminal capacitance technique. The thermal expansion was negative near the transition with a peak at 115 K. Between 30 and 115 K a relaxation was observed in the magnetostriction. Above a temperature-dependent critical field a step increase in field results in an immediate step increase in length but then the length begins to decrease approximately logarithmically with time. The length relaxes noticeably for at least 1 h and the final length is often shorter than the equilibrium length before the field change. No relaxation was observed above the transition. These effects can be explained by the intimate coupling between magnetic and crystal symmetries which give rise to a crystalline axis switching mechanism.