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MA: Fachverband Magnetismus
MA 51: Magnetic Shape Memory Alloys (Joint Session with MM)
MA 51.5: Vortrag
Freitag, 20. März 2015, 10:30–10:45, H 0112
Ordering kinetics in Ni-Mn based ferromagnetic shape memory alloys — •Pascal Neibecker1, Michael Leitner1, Georg Benka2, and Winfried Petry1 — 1Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstr. 1, 85748 Garching, Germany — 2Physics Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
Ni-Mn based Heusler alloys of the type Ni2MnX have gained significant interest in recent years due to their magnetic shape memory properties. These alloys usually crystallize in the high temperature B2 phase and undergo at lower temperatures first a transition to the higher ordered L21 phase and later to a variant-rich martensitic phase.
Yet, the existence and characteristics of the martensitic transition as well as the temperature of the magnetic transition are heavily dependent on the degree of L21-type order adjusted in the alloy. While in Ni2MnGa, the degree of L21 order is inherently high, other promising alloys such as Ni2MnAl are lacking thereof.
In this respect, we report on the kinetics of L21 order adjustment in Ni2MnAl, both in the case of thermodynamic equilibrium vacancy concentrations and in the case of quenched-in vacancy excess. We demonstrate the acceleration of ordering kinetics under vacancy excess, which permits the adjustment of hitherto unreachable states of order in the Ni2MnAl system. Our results were obtained employing Differential Scanning Calorimetry (DSC), magnetic measurements using a Physical Property Measurement System (PPMS) as well as X-ray Powder Diffractometry (XRD).