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.
N.N. SARAWATE and M.J. Dapino, “Magnetic field induced stress and magnetization in mechanically-blocked Ni-Mn-Ga,” Journal of Applied Physics, Vol. 103, Issue 8, 083902, 16 April 2008.