Abstract
With a high Curie temperature and low entropy change, the magnetic-field-induced martensitic transformation has been obtained in ferromagnetic shape memory alloys MnNiGa by doping a small amount of Co. Due to the ferromagnetic activation effect of Co, a large amount of antiferromagnetically aligned Mn moments are turned into ferromagnetic ordering, which is verified by our electronic structural calculation and experimental observation. Consequently, the magnetization rises up to 70 emu/g and the magnetization difference between two phases increases about ten times, resulting in a considerable dT/dH of 4 K/T and a well-defined reversed transformation induced by a magnetic field. (c) 2008 American Institute of Physics.