HYSTERETIC EVIDENCE FOR FINITE ORDERED DOMAINS IN CONTINUOUS VERWEY TRANSFORMATIONS

Low temperature x-ray diffraction experiments on Fe3(1-delta)O4 single crystals (delta = 0.0045) with a modified precession camera reveal diffraction patterns indexable with the same base centered monoclinic unit cell of stoichiometric Fe3O4. The intensity at (8 0 1/2), representative of the characteristic doubling of the spinel unit cell associated with Verwey ordering, increases gradually below a transformation temperature (T(V)II = 99 K) consistently with the continuous character observed for delta < delta(C) = 0.0039, in marked contrast with the discontinuous appearance of half-integer Bragg reflections below the first-order transition (T(V)I = 122 K) for delta = 0. Thermal hysteresis is observed in the satellite intensity beyond the percolation limit (delta(C)), which correlates with similar behavior in electrical resistivity and provides evidence for the existence of finite ordered domains. (C) 1994 Academic Press, Inc.