Berlin 2015 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 24: Magnetic Materials I
MA 24.5: Vortrag
Mittwoch, 18. März 2015, 10:30–10:45, H 0112
Direct measurements of the magnetocaloric effect in thin film and low volume samples — •Jago Döntgen1, Jörg Rudolph1, Tino Gottschall2, Oliver Gutfleisch2, Steffen Salomon3, Alfred Ludwig3, and Daniel Hägele1 — 1AG Spektroskopie der kondensierten Materie, Ruhr-Universität Bochum, Germany — 2Functional Materials, TU Darmstadt, Germany — 3Werkstoffe der Mikrotechnik, Ruhr-Universität, Bochum, Germany
We present the first temperature dependent measurements of the magnetocaloric effect in a Gd thin film with sub-mK resolution. The high sensitivity of our newly developed technique of magnetomodulation combined with detection of the sample’s thermal radiation allows the systematic investigation of thin film material libraries grown on wafers and gives new insights into the low-field behaviour of the magnetocaloric effect, which is not accessible by traditional calorimetry.
At TC, we find a quadratic magnetic field dependence of the magnetocaloric Δ T for low external fields, contradicting earlier predictions. The same behaviour is found in bulk Gd and the metamagnetic alloy LaFe11.05Co0.91Si1.04, underlining the versatility of our approach. An analytic expression based on Landau theory is found, that describes the transition of Δ T from the Hext2 behaviour at low to the well-known Hext2/3 behaviour at high fields.