The magnetostructural transition and magnetocaloric properties in Fe0.6Mn0.4NiSi1-xAlx alloys

The Fe0.6Mn0.4NiSi1-xAlx (x=0, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, and 0.12) alloys were prepared by arc melting and annealed at 1073K for 90h. With increasing Al contents, the structure of Fe0.6Mn0.4NiSi1-xAlx changes from TiNiSi-type to Ni2In-type at room temperature, while the Curie temperature decreases from 390K to 136K. Although the refrigerant capacity is relatively small, about 126J/kg, the maximum isothermal entropy change reaches a value of -Delta S-max=52.9J/(kgK) under 5T for x=0.04. At the same time, the alloys have great corrosion resistance. From x=0 to 0.12, samples can be tuned from a second-order to a first-order and then to a second-order phase transition. It is worth noting that there is no magnetic hysteresis for all samples although they experience structural phase transition. The structural and magnetic phase diagrams of the Fe0.6Mn0.4NiSi1-xAlx system have been figured out. The results indicate that the relatively large magnetocaloric effects with no magnetic hysteresis and good corrosion resistance make these alloys a good candidate for magnetic refrigeration near room temperature.