Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy

Salazar Mejía, C. and Born, N.-O. and Schiemer, J. A. and Felser, C. and Carpenter, M. A. and Nicklas, M. (2018) Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy. Physical Review B, 97 (9). ISSN 2469-9950 DOI https://doi.org/10.1103/PhysRevB.97.094410

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Abstract

Resonant ultrasound spectroscopy and magnetic susceptibility experiments have been used to characterize strain coupling phenomena associated with structural and magnetic properties of the shape-memory Heusler alloy series Ni 50 + x Mn 25 − x Ga 25 ( x = 0 , 2.5, 5.0, and 7.5). All samples exhibit a martensitic transformation at temperature T M and ferromagnetic ordering at temperature T C , while the pure end member ( x = 0 ) also has a premartensitic transition at T P M , giving four different scenarios: T C > T P M > T M , T C > T M without premartensitic transition, T C ≈ T M , and T C < T M . Fundamental differences in elastic properties, i.e., stiffening versus softening, are explained in terms of coupling of shear strains with three discrete order parameters relating to magnetic ordering, a soft mode, and the electronic instability responsible for the large strains typical of martensitic transitions. Linear-quadratic or biquadratic coupling between these order parameters, either directly or indirectly via the common strains, is then used to explain the stabilities of the different structures. Acoustic losses are attributed to critical slowing down at the premartensite transition, to the mobility of interphases between coexisting phases at the martensitic transition, and to mobility of some aspect of the twin walls under applied stress down to the lowest temperatures at which measurements were made.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA74
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Physical Review B
Volume: 97
Identification Number: https://doi.org/10.1103/PhysRevB.97.094410
Depositing User: Sarah Humbert
Date Deposited: 18 May 2018 10:52
Last Modified: 18 May 2018 10:52
URI: http://eprints.esc.cam.ac.uk/id/eprint/4277

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