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The structure, phase transitions, magnetocaloric effect, and exchange bias effect in Mn 49 Ni 42- x Co x Sn 9 ( x  = 0, 1, 3 and 5) ferromagnetic shape memory alloys have been systematically investigated. X-ray diffraction results measured at room temperature reveal that Mn 49 Ni 42- x Co x Sn 9 alloys with x  = 0, 1 present martensite structure, and Mn 49 Ni 42- x Co x Sn 9 alloys with x  = 3, 5 exhibit mixture phases of both martensite and austenite. The martensitic transformation and exchange bias field ( H EB ) 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 Mn 49 Ni 37 Co 5 Sn 9 alloy. We realized a continuous tuning of the H EB from 534.7 Oe to 1113.0 Oe after field cooling in presence of 10 kOe. [ABSTRACT FROM AUTHOR]

We have systematically investigated the exchange bias (EB) effect and low-temperature magnetic state transition in Mn 42 Cu 6 Ni 42 Sn 10 Heusler alloy by means of AC and DC magnetization measurements. Experimental results suggest that the martensitic phase is in the state of superparamagnetic (SPM), following that the particles turn into the ferromagnetic (FM) state at the martensitic Curie temperature, and the moments are frozen as the temperature is below 150 K. In addition, EB effect was observed in the phase separated martensitic state, which can achieves about 536 Oe under the field of 500 Oe after field-cooled (FC) to 10 K. First-principle investigations indicate that such a small value is originated from nonmagnetic Cu atoms substitution. The appearance of EB effect can be ascribed to the competition between the FM martensitic phase and spin glass (SG) phase due to the impact of Mn atoms, whereas the nonmagnetic Cu atoms doping would hinder the magnetic aggregation, resulting the small EB value eventually. [ABSTRACT FROM AUTHOR]