The phase transitions, magnetocaloric effect, and exchange bias in Mn49Ni42-xCoxSn9 alloys

The structure, phase transitions, magnetocaloric effect, and exchange bias effect in Mn49Ni42-xCoxSn9 (x = 0, 1, 3 and 5) ferromagnetic shape memory alloys have been systematically investigated. X-ray diffraction results measured at room temperature reveal that Mn49Ni42-xCoxSn9 alloys with x = 0, 1 present martensite structure, and Mn49Ni42-xCoxSn9 alloys with x = 3, 5 exhibit mixture phases of both martensite and austenite. The martensitic transformation and exchange bias field (HEB) are very sensitive to the Co content. In addition, large positive magnetic entropy changes were observed in these alloys due to the magnetic-field-induced transition from the paramagnetic martensitic phase to the ferromagnetic austenitic phase, and a large effective refrigeration capacity of 230.8 J/kg was obtained under the magnetic field change of 70 kOe in Mn49Ni37Co5Sn9 alloy. We realized a continuous tuning of the HEB from 534.7 Oe to 1113.0 Oe after field cooling in presence of 10 kOe.