Multifunctional Properties of Ni-Mn-Y (Y = In, Ga) Based Heusler Alloys

Arjun Pathak (Southern Illinois University)

The Ni-Mn-based Heusler alloys encompass a rich collection of useful materials from highly spin-polarized systems to shape memory to magnetocaloric alloys. Some Heusler alloys offer an excellent opportunity to investigate the various aspects of magnetic and structural phase transformations in a single system. In this talk I will summarize how subtle interplay between magnetic and structural degrees of freedom give rise to multifunctional properties such as magnetocaloric effect, magnetoresistance (MR), exchange bias (EB) effect and giant Hall effect (GHE) in off-stoichiometric Ni-Mn-Y (Y=In, Ga) based Heusler alloys. More interestingly, often two or more of these properties exist in the same material, making them prototypical multifunctional materials. The phase transitions and respective magnetic entropy changes (.SM) strongly depend on composition in these systems. The inverse .SM was found to be more than 80 J.Kg-1.K-1 (for H=5 T) near the room temperature for the In-based alloys. The zero field and field cooled magnetization curves of some of Ni50Mn50-xInx were found to split at low temperature region that is indicative of the presence of inhomogeneous magnetic states. This results in EB of more than 120 Oe at 5 K for x=15. The Hall resistivity (.H) and the Hall angle shows unusual behavior in the vicinity of the martensitic phase transition for Ni50Mn50-xInx with x=15.2. Significantly large inverse .SM and MR were also observed for Ni50-xCoxMn32-yFeyGa18. The phase transition temperatures and magnetic properties of Ni50-xCoxMn32-yFeyGa18 were found to be correlated with the degree of tetragonal distortion. Our studies give fundamental insight as to how tweaking material properties it is possible to get technologically important and scientifically interesting materials.

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