The effect of pressure on the magnetic and structural transition temperatures of the shape memory alloys Ni50+x(Mn0.5Fe0.5)25Ga25–x

The effect of pressure on the Curie temperature TC and the martensitic transition temperature TM of the ferromagnetic shape memory alloys Ni50+x(Mn0.5Fe0.5)25Ga25–x has been investigated by measuring the temperature dependence of the initial permeability at various pressures up to ~~10 kbar. The pressure derivatives of TC and TM, dTC/dp and dTM/dp, of Ni50(Mn0.5Fe0.5)25Ga25 (x=0) are found to be 0.23 K/kbar and 0.77 K/kbar, respectively. The values of dTC/dp and dTM/dp of Ni50+x(Mn0.5Fe0.5)25Ga25–x alloys decrease with increasing x. Moreover the sign of dTC/dp changes from positive to negative with increasing x. The pressure dependence of TC for Ni50+x(Mn0.5Fe0.5)25Ga25–x alloys is discussed qualitatively based on the dependence of the exchange interactions on interatomic distance.