Magnetic Entropy Change and Electrical Transport Properties of Bilayered Perovskite Manganite La1.2-xTbxSr1.8Mn2O7(x=0,0.05)

The polycrystalline samples of double-layered perovskite manganite La1.2-xTbxSr1.8Mn2O7 (x=0, 0.05) were prepared by traditional solid state reaction method. The nature of magnetic phase transitions, the magnetic entropy change and possible applications in magnetic refrigeration were explored by measuring and analyzing magnetization curves M(H, T). In the temperature range measured, the samples with x=0 and 0.05 showed paramagnetic behavior at high temperature. At lower temperature, the samples with x=0 and 0.05 formed a two-dimensional short-range order at TC2D=245 and 225 K, and then formed an three-dimensional long-range ferromagnetic order at TC3D=120 and 70 K, respectively; when at further lower temperature below TC3D, both samples showed cluster spin glass behavior. Near the TC3D, the sample with x=0 exhibited the characteristic of a first-order transition and gave a maximum magnetic entropy change of 2.17 J·(kg·K)-1 under a 2 T magnetic field, while the sample with x=0.05 only displayed a continuous second-order transition and gave maximum magnetic entropy change of 1.6 J·(kg·K)-1. Therefore, the two samples were beneficial to the application of Erickson magnetic refrigeration cycle. In addition, the electrical transport properties of the samples were investigated by resistivity-temperature (ρ-T) curve. The results showed that the x=0 sample and the x=0.05 sample appeared an insulator-metal transition (TP) at 96 and 93 K, respectively. The fitting to ρ-T curves at temperatures above TP showed that, the electron conducting mechanism of both samples could be attributed to three-dimensional variable-range hopping in the high temperature range. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.