Powder neutron diffraction studies of Zn-doped magnetite

We report on systematic neutron powder diffraction measurements of the temp erature dependence of the crystal structure for the Fe3-xZnxO4 (x < 0.036) series. Time-of-flight data were collected on the spallation source ISIS (R AL, UK) between 4.2 and 270 K for samples showing different orders of the V erwey transition. The change of transition order is accompanied by the clea r difference in the characteristic low temperature rhombohedral distortion. Namely, this distortion is independent of the dopant concentration for sam ples undergoing a first order Verwey transition, while the distortion for s amples showing second order transition is much smaller and gradually dimini shes with increasing Zn content. This distinct behaviour is linked to a cha nge of atomic ordering from a well defined configuration for the first orde r regime to a dynamically changed arrangement for highly doped magnetite. T his points to a close connection between the order of the Verwey transition and crystal lattice properties.