Magnetostructural phase transition and magnetocaloric effect in off-stoichiometric Mn1.9-xNixGe alloys

Phase transitions and magnetic entropy changes are studied in Mn1.9-xNixGe (x = 0.85, 0.855) alloys. In these off-stoichiometric alloys, the crystallographic transition temperature decreases remarkably due to the deficiency of transition-metal atoms, and, consequently, a magnetostructural transition from the antiferromagnetic TiNiSi-type structure to the ferromagnetic Ni2In-type structure is observed. Owing to the abrupt change in magnetization, large magnetic entropy changes are obtained. The effect of transition-metal vacancies on the phase transition temperature is discussed. (C) 2008 American Institute of Physics.