Stress-assisted magnetic-field-induced strain in Ni-Fe-Ga-Co ferromagnetic shape memory alloys

To obtain a large strain for Ni-Fe-Ga ferromagnetic shape memory alloys, the Curie temperature was increased by adding Co, and the magnetic-field-induced strain (MFIS) has been investigated under static stresses. The magnetocrystalline anisotropy constant K is increased by the addition of Co, and Ni49 Fe18 Ga27 Co6 alloy gives a relatively large value of 1.15× 106 erg cm3 at 300 K. From the stress-strain curves for this alloy, the twinning stress is estimated to be 8-9 MPa. Consequently, the Ni49 Fe18 Ga27 Co6 alloy exhibits a large MFIS of about 8.5% at room temperature under a static compressive stress of about 8 MPa.