Hydrostatic pressure tuned magneto-structural transition and occurrence of pressure induced exchange bias effect in Mn_0.85Fe_0.15NiGe alloy

The magnetic and magneto-functional behavior of a Fe-doped MnNiGe alloy with nominal composition Mn_0.85Fe_0.15NiGe have been investigated in ambient as well as in high pressure conditions. The alloy undergoes a first order martensitic phase transition (MPT) around 200 K and also shows a large conventional magnetocaloric effect (MCE) ($\Delta S\sim -21$ J kg⁻¹ K⁻¹ for magnetic field (H) changing from 0–50 kOe) around the transition in ambient conditions. The application of external hydrostatic pressure (P) results in a shift in MPT towards the lower temperature and a clear decrease in the saturation moment of the alloy at 5 K. The peak value of MCE is also found to decrease with increasing external P (∼18 J kg⁻¹ K⁻¹ decrease in $\Delta S$ has been observed for P  =  12.5 kbar). The most interesting observation is the occurrence of the exchange bias effect (EBE) on application of external P. The competing ferromagnetic and antiferromagnetic interaction in the presence of external P plays the pivotal role towards the observation of P induced EBE. (paper)