The effect of average A-site cation radius on TC in perovskite manganites

Three series of samples Ln0.7T0.3MnO3 (I), Ln0.7T0.3Mn0.9Cr0.1O3 (II), and Ln0.7T0.3Mn0.9Fe0.1O3 (III) (Ln=La, (La, Nd), (La, Y), T=Ca, CaSr, Sr) were prepared by sol-gel technique. The effect of the average A-site cation radius on the ferromagnetic transition temperature TC has been investigated. TC was obtained from M-T curves measured by vibrating sample magnetometer. For a little Nd3+ doped at the A-site, the TC of Ln0.7T0.3MnO3 (I) drops linearly with decreasing (1.18 A<<1.25 A). Similar behavior has been observed in series II and III, which have lower TC values than series I due to the weakening of the influence of double-exchange interactions upon substituting Fe and Cr for Mn