Giant magnetic-field-induced strain in Ni-Mn-Ga crystals: Experimental results and modeling

Strains up to 6% have been induced by application of magnetic fields of 320-400 kA/m (4-5 kOe) to Ni-Mn-Ga single-crystal ferromagnetic shape memory alloys at room temperature. The blocking stress (stress at which field-induced strain is zero) is in the range 1.5-2MPa. These strains are not magnetostrictive in origin but arise rather from field-induced motion of twin boundaries in the martensitic phase. A thermodynamic model for field-induced twin-boundary motion describes the main features of the field dependence and stress dependence of the strain. All parameters of the model can be measured from experimental stress vs. strain and magnetization vs. field curves. (C) 2001 Elsevier Science B.V. All rights reserved.