MAGNETOCALORIC EFFECT AND REDUCTION OF HYSTERESIS IN Tb{sub}5Si{sub}(2-x)Ge{sub}(2-x)M{sub}(2x) (0 ≤ 2x ≤ 0.1; M=Fe, Pb, Mn) COMPOUNDS

摘要

Large magnetocaloric effect has been observed in Tb{sub}5Si{sub}2Ge{sub}2 around 111 K. The influence of alloying this parent compound with Fe, Pb and Mn on the phase formation, Curie temperature, hysteresis loss and magnetic entropy change have been studied by X-ray powder diffraction and magnetic measurements. It has been observed that each alloying process has considerably different consequences on these parameters. Although the Curie temperature was observed to remain almost unchanged in this alloying range, the magnetic entropy change values were severely affected especially with Mn replacement. Very large magnetic entropy change values were obtained for the first time with commercial grade starting materials. On the other hand Pb alloying did not increase the magnitude of magnetic entropy change as is reported for other compounds like Gd{sub}5Si{sub}2Ge{sub}2. First order phase transformation apparent in the parent alloy is immediately lost even with small additions of Fe as the alloying elements. This observation suggests a significant reduction of magnetic hysteresis which is important for magnetic refrigeration applications. The crystal structure modifications and imperfections introduced by alloying have also been observed to play significant roles in the magnetic model.