Magnetic field-induced martensitic transformation and giant magnetostriction in Fe-Ni-Co-Ti and ordered Fe3Pt shape memory alloys

The effect of a magnetic field on martensitic transformations in Fe-Ni-Co-Ti and Fe3Pt shape memory alloys has been examined in order to know a magnetic field-induced martensitic transformation and a control of crystallographic domain (variant) by magnetic field. Following results were obtained: (i) Magnetoelastic martensitic transformation (martensites are induced only while a magnetic field is applied and are transformed back to the parent phase when the magnetic field is removed.) appears in an ausaged Fe-Ni-Ti-Co shape memory alloy. The critical magnetic field for inducing a magnetoelastic martensitic transformation increases with increasing temperature. Volume fraction of martensite induced depends on the strength of the magnetic field. (ii) Magnetic field controls perfectly the crystallographic domain (variant) in a martensite state of an ordered Fe3Pt, which exhibits a martensitic transformation from a cubic parent phase to a tetragonal martensite phase. In addition, a giant magnetostriction of about 5 x 10(-3) was realized under a magnetic field of up to 3.2 MA/m, which is nearly three times as large as that of Terfenol-D (Fe2DyxTb1-x).