ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Electrical transport properties of synthetic magnetite (Fe3(1−δ)O4) single crystals of controlled stoichiometry have been characterized by ac impedance measurements between 5 Hz and 10 MHz, as a function of temperature (77 K〈T〈300 K) above and below Verwey temperatures (Tv) of first- (δ≈0) and second-order (δ≈0.005) transitions. The low-frequency impedence is in agreement with results obtained by dc methods. For T〈Tv, samples in both composition regimes exhibit weak frequency dependence. Above the magnetic isotropic temperature (Tm≈130 K), the high-frequency impedance increases with relatively constant phase angle. Local maxima at high frequencies are observed in log ||z||−1/T space, at temperatures corresponding to Tm. In this projection, the δ≈0.005 sample exhibits an anomalous frequency dependence at approximately 250 K. Between Tm and Tv, the frequency dependence diminishes with decreasing temperature, vanishing at roughly 110 K. Above Tv, the observed behavior is shown to be a function of permeability, which has no influence below Tv. For T〈Tv, the results support an adiabatic hopping conduction mechanism.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.342266
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