Observation of thermally-induced magnetic relaxation in a magnetite grain using off-axis electron holography

Abstract

A synthetic basalt comprising magnetic Fe3O4 grains (∼ 50 nm to ∼ 500 nm in diameter) is investigated using a range of complementary nano-characterisation techniques. Off-axis electron holography combined with in situ heating allowed for the visualisation of the thermally-induced magnetic relaxation of an Fe3O4 grain (∼ 300 nm) from an irregular domain state into a vortex state at 550C, just below its Curie temperature, with the magnetic intensity of the vortex increasing on cooling.