Regensburg 2019 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 35: Caloric effects in ferromagnetic materials

MA 35.6: Vortrag

Mittwoch, 3. April 2019, 16:15–16:30, H52

Millisecond Dynamics of the Magnetocaloric Effect in a First- and Second-Order Phase Transition Material — •Jago Döntgen, Jörg Rudolph, and Daniel Hägele — AG Spektroskopie d. kond. Materie, Ruhr-Universität Bochum

One of the key challenges of the research in magnetocaloric materials is a reliable determination of the adiabatic temperature change Δ T. We have developed a novel method for direct measurements of Δ T that allows for the investigation of the magnetocaloric effect on length- and time-scales inaccessibly by traditional calorimetry. Our technique is based on the application of temporally oscillating magnetic fields and detection of the resulting change of the thermal radiation emitted by the sample. We achieve a unique combination of a sensitivity of better than 1 mK, a time-resolution of 10 µs, and magnetic field modulation frequencies exceeding 1 kHz [1]. We present dynamic measurements of the magnetocaloric effect, that allow for a direct distinction between reversible and irreversible sample behavior. The Δ T dynamics of the first-order phase transition material La_1.2Fe_11.4Si_1.4Mn_0.2H_y show a peculiar self-quenching at temperatures slightly below the peak maximum.[2] This behavior can be attributed to the first-order nature of the phase transition, which takes place at the phase boundary between the paramagnetic and ferromagnetic sample regions.

[1] Döntgen et al., Rev. Sci. Instrum. 89, 033909 (2018)

[2] Döntgen et al., Energy Technol. 6, 1470-1477 (2018)