Phase transformation, magnetic properties, and exchange bias of Heusler alloy Mn<sub>50–x</sub>Cr<sub>x</sub>Ni<sub>42</sub>Sn<sub>8</sub>

Abstract

In this paper, phase transformations, magnetic properties and exchange bias of Mn<sub>50–<i>x</i></sub>Cr<sub><i>x</i></sub>Ni<sub>42</sub>Sn<sub>8</sub> (<i>x</i> = 0, 0.4, 0.6, 0.8) polycrystalline samples are investigated. It is found that each of all the alloys has a tetragonal martensite structure at room temperature. The transformation temperature decreases with the increase of Cr content. The maximum magnetization difference between martensite and austenite phase is ∆<i>M</i> = 7.61 emu/g. The change of magnetic properties is mainly related to the change of Mn-Mn distance and the hybridization strength between Ni(A)-Mn(D). The ferromagnetism of martensite can be enhanced by Cr doping. The exchange bias field is observed to reach up to as high as 2624 Oe in Mn<sub>50</sub>Ni<sub>42</sub>Sn<sub>8</sub> alloy after cooling from room temperature to 5 K in 500 Oe magnetic field, which decreases gradually with the increase of Cr content. Furthermore, the exchange bias field increases first and then followed by a decrease with the increase of the cooling field in Mn<sub>49.2</sub>Cr<sub>0.8</sub>Ni<sub>42</sub>Sn<sub>8</sub>. This is mainly attributed to the change of the interface exchange coupling between the spin glass state and antiferromagnetic region.