Structural, thermal, magnetic, and transport properties of (La2/3Ca1/3) (Mn1-xSnx)O3-δ compounds

The structural, magnetic, and electrical transport properties of Sn-doped manganite La0.67Ca0.33Mn1_chiSnchiO3-delta (x = 0, 0.01, 0.03, and delta approximate to 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 T-C and the metal-insulator transition temperature TM-I decreased nonlinearly with increasing Sn content. The T-C and TM-I values, for the chi = 0, 0.01, and 0.03 compounds were separated by 18.2 K, 66.3 K, and 10 K, respectively. The resistivity above TC for all of these compounds followed the Mott variable-range-hopping model. This allowed the estimation of the localization lengths of 2.2 Angstrom (chi = 0), 1.33 Angstrom (chi = 0.01) and 1.26 Angstrom (chi = 0.03). The x. = 0 and x = 0.01 compounds exhibited anomalies of R(T) at corresponding Tc and allowed the separation of the magnitude of the purely magnetic contribution to the resistance which for chi = 0 was approximate to 5.7 Ohm and for chi = 0.01, approximate to 22.4 Ohm. 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. Our results on La(0.67)Ca(0.33)Mn(1-chi)SnxO(3) reveal that a small substitution of Sn 4(+) for Mn 4(+) suppresses double exchange interactions and strongly affects the magnetic, thermal, and transport properties of the parent compound.