Structural, Thermal, Magnetic, and Transport Properties of (La$\text{}_{2}\text{}_{/}\text{}_{3}$ Ca$\text{}_{1}\text{}_{/}\text{}_{3}$ )(Mn$\text{}_{1-x}$Sn$\text{}_{x}$)O$\text{}_{3-δ}$ Compounds

The structural, magnetic, and electrical transport properties of Sn-doped manganite La$\text{}_{0.67}$Ca$\text{}_{0.33}$Mn$\text{}_{1-x}$ Sn$\text{}_{x}$O$\text{}_{3-δ}$ (x=0, 0.01, 0.03, andδ≈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$\text{}_{C}$ and the metal-insulator transition temperature T$\text{}_{M-I}$ decreased nonlinearly with increasing Sn content. The T$\text{}_{C}$ and T$\text{}_{M-I}$ 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$\text{}_{C}$ 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$\text{}_{C}$ and allowed the separation of the magnitude of the purely magnetic contribution to the resistance which for x=0 was≈5 .7Ω and for x=0.01,≈22 .4Ω. The specific heat of the Sn-free sample exhibited a sharp peak at T$\text{}_{C}$. With increasing Sn content the peak at T$\text{}_{C}$ broadened and the area under the peak decreased. For x= 0.03 the peak was hardly detectable. Our results on La$\text{}_{0.67}$Ca$\text{}_{0.33}$ Mn$\text{}_{1-x}$Sn$\text{}_{x}$O$\text{}_{3}$ reveal that a small substitution of Sn$\text{}^{4+}$ for Mn$\text{}^{4+}$ suppresses double exchange interactions and strongly affects the magnetic, thermal, and transport properties of the parent compound.