Characterization of Ni-Mn-Ga Shape Memory Single Crystals for Magnetic Properties and Magnetic Field Induced Shear and Normal Strains

This paper presents a novel experimental apparatus and a test method for measuring simultaneously quasi-static average longitudinal and shear magnetic-field-induced strain (MFIS) of Ni-Mn-Ga single crystals. The apparatus consists of an aluminum casing, a weight-controlled plunger, two displacement probes (one vertical and one lateral), and a torsion guide etc. Three Ni-Mn-Ga square prism samples were tested. Twin boundary bands were clearly visible after the application of magnetic field. A range of material properties were measured. These include: (a) magnetic anisotropy constant; (b) single variant magnetization curves for the easy and hard axes; (c) nonlinear compressive stress-strain curves for all three samples at room temperature; and (d) average longitudinal and shear MFIS curves versus magnetic field strength for three prism samples subject to various compressive external stresses.