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MA: Fachverband Magnetismus

MA 55: Poster II

MA 55.79: Poster

Freitag, 4. April 2014, 10:30–13:30, P2

Conventional and inverse magnetocaloric effects at magnetostructural transitions in Mn-based compounds — •Franziska Scheibel¹, Öznur Cakir², Atakan Tekgül³, Mehmet Acet¹, and Michael Farle¹ — ¹Faculty of Physics and CENIDE, Universität Duisburg-Essen, D-47048 Duisburg, Germany — ²Physics Department, Yildiz Technical University, Davutpasa, Istanbul, Turkey — ³Physics Department, Akdeniz University, Antalya, Turkey

One key factor for efficient magnetic refrigeration is reversibility in the temperature-change on applying and removing the external magnetic field to the active magnetic refrigeration material. At magnetostructural transitions, where large entropy changes can occur, this occurs only in systems with sufficiently narrow thermal hysteresis at the transition. To understand how reversibility is related to hysteresis, entropy-changes and corresponding adiabatic temperature-changes are studied in Mn-rich Heusler alloys, anti-perovskites, and pnictides. We study the magnetization and the adiabatic temperature-change in the temperature range 5 ≤ T ≤ 380 K in magnetic fields up to 5 T using a SQUID magnetometer and a calorimeter, respectively. The structural properties are further investigated by x-ray diffraction. The results indicate that the occurrence of long range ferromagnetism in any one of the phases below or above the magnetostructural transition in the systems mentioned above is unfavorable for a reversible temperature change. In contrast, the presence of ferrimagnetism or enhanced paramagnetism leads to a narrow thermal hysteresis of the transition.
Work supported by the Deutsche Forschungsgemeinschaft (SPP 1599)