PAC measurements of the Verwey transition in magnetite

Perturbed angular correlation (PAC) experiments with implanted In-111 trace rs have recently been used to investigate magnetic phase transitions in met al oxides. Here we report on PAC measurements for Cd-111 in polycrystalline Fe3O4 in the neighborhood of the Verwey phase transition (T-V approximate to 120 K). Perturbed angular correlation spectra were taken for implanted I n-111 probes at temperatures between 9 and 850 K. The two observed Larmor f requencies are attributed to the two possible cation sites in the cubic inv erse spinel lattice. For T > 120 K, the temperature dependence of both Larm or frequencies follows a Curie-Weiss power law omega(L)(T)/omega(L)(0) = (1 - T/T-N)(beta), with the parameters T-N = 848(2) K and beta = 0.392(2). At the Verwey temperature we find a rapid change of both Larmor frequencies, with omega(L1) increasing from 178(2) MHz at 120 K to 191(4) MHz at 100 K, and omega(L2) decreasing from 173(4) MHz to 151(5) MHz. The Verwey transiti on also affects the widths of the frequency distributions, which more or le ss double below T-V. This possibly indicates the presence of several compon ents with Larmor frequencies similar to those found in the previous Mossbau er data, or for electronic after-effects correlated with the semiconductivi ty of magnetite below T-V.