The structural, magnetic, and electrical transport properties of Sn-doped manganite La0.67Ca0.33Mn1−xSnxO 3−δ (x = 0, 0.01, 0.03, and δ ≈ 0.06) compounds were studied using X-ray powder diffraction, scanning electron microscopy, AC susceptometer and vibrating sample magnetometer measurements as well as four-probe resistance measurements. The specific heat was measured by the heat-pulse method. The Curie temperature TC and the metal-insulator transition temperature T M−I decreased nonlinearly with increasing Sn content. The TC and TM−I values, for the x = 0, 0.01, and 0.03 compounds were separated by 18.2 K, 66.3 K, and 10 K, respectively. The resistivity above T C for all of these compounds followed the Mott variable-range-hopping model. This allowed the estimation of the localization lengths of 2.2Å (x = 0), 1.33Å (x = 0.01) and 1.26Å (x = 0.03). The x = 0 and x = 0.01 compounds exhibited anomalies of R(T ) at corresponding T C and allowed the separation of the magnitude of the purely magnetic contribution to the resistance which for x = 0 was ≈ 5.7 Ω and for x = 0.01, ≈ 22.4 Ω. The specific heat of the Sn-free sample exhibited a sharp peak at TC. With increasing Sn content the peak at TC broadened and the area under the peak decreased. For x = 0.03 the peak was hardly detectable.

Studies of the specific heat and simultaneous AC magnetic susceptibility (χ ) and electric resistance of stoichiometric magnetite single crystal are presented. The temperature hysteresis of the Verwey transition is of 0.03 K found from the specific heat data confirming its first-order character. The continuous temporal change of χ at T V can be switched off by an external magnetic field without affecting the transition. The electrical resistance decreases continuously with increasing temperature with a rapid change of slope at the point when the phase transition is completed. It was concluded that the magnetic degrees of freedom do not actively participate in the transition and that the entropy released at TV may come from ordering electrons.

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