Specific Heat and Electrical Conductivity of Low temperature Phase of Magnetite

Abstract

It was observed for Fe 3 O 4 that the presence of residual stresses lowers the so-called Verwey temperature, T v , considerably, broadens the temperature-width of the anomalous specific heat at T v , produces another additional peak and decreases the discontinuous conductivity change at T v . The entropy change at the phase transition was determined to be 5.4 J /mole·deg but when the effect of short range order is included it becomes 9.6 which is much larger than the value expected for electron hopping under the Anderson's restriction. The anisotropic conductivity was measured below T v along the monoclinic axes a , b and c . The magnitude of conductivity was in the order of σ c >σ b >σ a in the range of T v > T >60 K, while it changed to σ b >σ a >σ c below 60 K. The conductivity along [\bar111], or the longest <111>, was also measured by using a squeezed crystal in which a monoclinic single domain is realized. This direction was least conductive among four <111>'s in the whole temperature range.