Date: 18-23 June 2017
Donostia-San Sebastian, Spain
Ni-Fe-Ga Heusler-type alloys is a promising candidate for solid-state room temperature refrigeration due to its large reversible elastocaloric effect [1, 2]. One of the few disadvantages is their production process that consists of arc-melting of pure element followed by long-term annealing. In contrary, rapid-quenching method is found to be a fast way to produce a large amount of samples in a single step. Here, we report on martensitic phase transition in Cu-doped Ni-Fe-Ga ribbons, prepared by melt spinning method. Austenitic L21 cubic phase was found at room temperature along with amorphous hallo (Fig. 1a). Twinning effect with period of 180-300 nm was observed on the free surface (surface that had no contact with the wheel) within 40-60 micron crystallites (Fig. 1c). This is related to the residual martensitic phase in the film. Martensitic transition temperatures were obtained from resistivity curves and DSC measurements. Resistivity curves show traditional step-like behavior indicating martensitic phase transition (Fig. 1b). DSC curves demonstrate two overlapped peaks for both cooling and heating processes that can be related to premartensitic phenomena (Fig. 1d). Average martensitic transition temperature Tm was evaluated to be 264 K (from resistivity curves) and 273 K (from DSC). Low-field (0.01 T) thermomagnetic curves show small temperature hysteresis in the same area confirming the martensitic phase transition. Curie temperature value Tc = 269 K was evaluated by tangential method. It was also found that magnetic field has a negligible influence on martensitic transition temperatures (Fig. 1e).
Fig 1. a) XRD pattern made at RT; b) Thermomagnetic and resistivity curves; c) SEM images of the free surface; d) DSC heating/cooling curves; e) Resistivity curves measured in magnetic field of 1, 2 and 5 T
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S. Shevyrtalov1 , R. Varga2 , T. Ryba2 , M. Gorshenkov3 , V. Rodionova1
1 Center for Functionalized Magnetic Materials, Immanuel Kant Baltic Federal University, 236041, Kaliningrad, Russian Federation
2 Institute of Physics, Faculty of Science, P.J. Safarik University, Park Angelinum 9, 041 54, Kosice, Slovakia
3 National University of Science and Technology MISiS, 4, Leninskii Pr., Moscow, 119049, Russia
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Immanuel Kant Baltic Federal University,
Gaidara 6, Kaliningrad, 236022, Russia