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Field induced structural modifications and magnetocaloric effects in martensitic Heusler alloys

Mehmet Acet 1Seda Aksoy 1Pascale Deen 3Eberhard F. Wassermann 1Xavier Moya 2Lluís Mañosa 2Antoni Planes 2

1. Duisburg-Essen University, Experimental Physics, Lotharstr. 1, Duisburg D-47048, Germany
2. Universitat de Barcelona, Departament d'Estructura i Constituents de la Materia, Barcelona 08028, Spain
3. Institut Laue Langevin (ILL), Avenue des martyrs, Grenoble 38042, France

Abstract

Applying a magnetic field to ferromagnetic systems in the temperature vicinity of a first order structural transition can lead to magnetic field induced structural modifications and large magnetocaloric effects. Many Ni-Mn-based ferromagnetic Heusler alloys undergo first order martensitic transformations. Applying a magnetic field at temperatures close to the transition causes large field-induced strains and large magnetocaloric effects. In many of these systems, the field-induced strain is due to a field-induced reverse martensitic transformation to the austenitic state. The magnetocaloric effect around the transition is ‘inverse’, in which case the sample cools on applying a field as opposed to the ‘conventional’ case where it warms. In order to gain more insight into the mechanism of the large field-induced strains and the inverse magnetocaloric effect, we have performed diffuse polarized neutron diffraction experiments using the XYZ-polarization analysis technique. These experiments reveal the development of strong antiferromagnetic correlations just below the martensitic transition temperature. We discuss the relationship of these correlations with the inverse magnetocaloric effect and the field-induced strains.

 

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Related papers

Presentation: Invited oral at E-MRS Fall Meeting 2008, Symposium C, by Mehmet Acet
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-17 19:14
Revised:   2009-06-07 00:48