Dresden 2011 – wissenschaftliches Programm
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SKM-SYDT: SKM-Symposium Diffusionless Transformations in Magnetic and Ferroelectric Bulk and Thin Films
SKM-SYDT 1: Diffusionless Transformations in Magnetic and Ferroelectric Bulk and Thin Films
SKM-SYDT 1.4: Hauptvortrag
Donnerstag, 17. März 2011, 12:00–12:30, TRE Ma
Nature of magnetic coupling in Ni-Mn-based martensitic Heusler alloys — •Mehmet Acet1, Seda Aksoy1, Eberhard F. Wassermann1, Lluis Manosa2, and Antoni Planes2 — 1Experimetalphysik, Universität Duisburg-Essen, 47048 Duisburg — 2Departament d*Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Diagonal 647, E-08028 Barcelona, Catalonia, Spain
To understand the cause of magnetic field induced effects in shape memory alloys, it is necessary to understand the nature of the magnetic coupling in the temperature-vicinity of the martensitic transition. Neutron diffraction, and neutron polarization analysis experiments on Ni-Mn-based martensitic Heusler systems show that at temperatures just below the martensitic transformation, the magnetic short-range correlations are antiferromagnetic in a spin-liquid type state. The correlations are mixed ferromagnetic and antiferromagnetic at temperatures above the martensitic transition; and well beyond the Curie temperature of the austenite state. The results of further ferromagnetic resonance studies show that antiferromagnetic exchange in the martensite state persists down to the lowest temperatures and coexists with the long-range ferromagnetism below the austenite Curie temperature. These results are also in line with the presence of a spin liquid state just below the martensitic transition.