Magnetic-field-induced stress and magnetization in mechanically blocked Ni–Mn–Ga

Abstract

A single-crystal Ni–Mn–Ga sample (AdaptaMat, Ltd.) is first compressed from its longest shape to a given bias strain and subsequently subjected to a slowly alternating magnetic field while being prevented from deforming. The tests are repeated for several bias strains. The available blocking stress, or maximum field-induced stress relative to the bias stress, is critical for quantifying the work capacity of a material. The largest available blocking stress for this material is 1.47 MPa at a bias strain of 3% and field amplitude of 640 kA/m. The work capacity calculated as the area under the available blocking stress versus bias strain curve is 72.4 kJ/m3. An existing continuum thermodynamics model for Ni–Mn–Ga sensors is augmented by incorporating the magnetoelastic energy as a source of stress generation when the material is mechanically blocked. The strain and magnetization are described by fixing the variant volume fraction.