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MA: Magnetismus

MA 19: Invited Talks Algarabel / Gutfleisch

MA 19.2: Hauptvortrag

Dienstag, 28. März 2006, 14:30–15:00, HSZ 03

Melt-spun materials for magnetic refrigeration near room temperature — •Oliver Gutfleisch — IFW Dresden, P.O. Box 270016, D-01171 Dresden, Germany

The development of giant magnetocaloric effect (MCE) materials could open the path for magnetic refrigeration near ambient temperature as an energy efficient, easily scaleable, mechanically simple and environmentally friendly cooling technology, by this replacing conventional refrigeration. Unlike in Gd5Ge2Si2, no magnetic-field induced crystallographic structural changes are involved in the large values of magnetic entropy change reported for LaFe13-xSix compounds of NaZn13-type structure and for MnFePAs compounds of Fe2P-type structure. LaFe11.8Si1.2 shows a thermally-induced first-order phase transition as well as an itinerant-electron metamagnetic transition accompanied by a significant volume change. A prolonged heat treatment is usually necessary to develop the NaZn13-phase in the bulk. Here, LaFe13-xSix was prepared by melt-spinning. Melt-spinning can yield refined microstructure, extended solute solubility, reduced macro- and micro-segregation and metastable phases. We succeeded in the preparation of the 1:13 phase by a much reduced annealing and in enhanced values of magnetic entropy changes. Curie temperature and the nature of the magnetic phase transition (shift from first-order to second-order) is adjusted by increasing Si content, by partially substituting Co for Fe or by interstitial hydrogen. These changes have not only consequences for the thermal and magnetic hysteresis but also affect the final net refrigerant capacity. A similar evaluation was done when replacing toxic As with Ge in melt-spun MnFePGe.