Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm.

Articles you may be interested inEffect of antiferromagnetic layer thickness on exchange bias, training effect, and magnetotransport properties in ferromagnetic/antiferromagnetic antidot arrays J. Appl. Phys. 115, 133909 (2014); 10.1063/1.4870285 Tuning exchange bias in ferromagnetic/ferromagnetic/antiferromagnetic heterostructures [Pt/Co]/NiFe/NiO with in-plane and out-of-plane easy axes

Unconventional exchange bias (EB) has been studied in CoCr2O4/Cr2O3 nanocomposites, in which the Curie temperature of the ferrimagnetic CoCr2O4 is much lower than the Néel temperature of the antiferromagnetic Cr2O3. A negative EB field of about 2.5 kOe at 5 K is achieved upon cooling in a field of 30 kOe. Meanwhile, the coercivity of the CoCr2O4 nanoparticles has been enhanced significantly by coupling with Cr2O3. The effect of the cooling field on the EB field and coercivity at 10 K has also been investigated. The domain-state model is used to interpret the unconventional EB. Cooling field may play a decisive role in the creation of the interfacial spin configuration for the unconventional EB, not only by exchange interaction between the induced magnetization of a polarized paramagnet and interfacial spins of an antiferromagnet but also by Zeeman interaction between the domain-state surplus magnetization and the external field.