Dresden 2009 – scientific programme

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MA: Fachverband Magnetismus

MA 14: Poster Ib: Magnetic Materials (1-14); Micro Magnetism/Computational Mag. (15-17); Surface Magnetism (18-22); Spin Structures/Phase Transitions (23-25)

MA 14.11: Poster

Tuesday, March 24, 2009, 10:15–13:00, P1B

Adiabatic temperature change in giant magnetocaloric effect compounds — Julia Lyubina, •Philipp Rosendahl, Jian Liu, Ludwig Schultz, and Oliver Gutfleisch — IFW Dresden, Institute for Metallic Materials, Helmholtzstr. 20, 01069 Dresden, Germany

The magnetic refrigeration based on the magnetocaloric effect (MCE) is becoming a promising technology to replace the conventional gas-compression/expansion technique. The two parameters, the adiabatic temperature change, ΔT_ad, and the magnetic entropy change, ΔS_M, are used for the evaluation of the MCE [1,2]. Most of the MCE studies are performed by indirect methods, among which the ΔS_M calculation using the Maxwell relation is the most widespread. Here, we report on direct adiabatic temperature change ΔT_ad measurements in giant MCE materials, La(Fe,Si)₁₃- and Ni-Mn-In Heusler-type alloys. ΔT_ad was measured using a direct contact with a thermocouple in magnetic fields up to 1.93 T produced by a permanent magnet assembly (Halbach cylinder). In Ni₅₀Mn₃₄In₁₆, the maximum ΔT_ad of 2 K is observed around the Curie temperature of the austenite (317 K), whereas ΔT_ad^max is -1.3 K near the martensite-austenite transition (181 K). On cooling, i.e. during the austenite-martensite transition, ΔT_ad^max reduces to about -0.5 K. In LaFe₁₂Si₁, the maximum ΔT_ad reaches -5.4 K at 184 K. The contribution of the latent heat to the adiabatic temperature change during first-order phase transitions is discussed. [1] J. Lyubina et al., J. Magn. Magn. Mater. 320 (2008) 2252; [2] J. Lyubina et al., Phys. Rev. Lett. 101 (2008) 177203.