Skirta Y. Electrical and magnetic properties of Ni-Mn-Ga and Fe-Mn-Ga Heusler alloys near the phase transition points

The structural, electrical and magnetic properties of Ni-Mn-Ga and Fe-Mn-Ga Heusler alloys were comprehensively investigated in the thesis. The features of the martensitic transitions in film and bulk monocrystalline samples of Ni-Mn-Ga and the influence of the structure and external factors on the transition temperatures were studied. With increasing film thickness increasing grain size. Changing the size of a grain temperature leads to a shift of phase transitions and changes in the magnetic and electrical properties of the films.The effect of the substrate and heat treatment on the structure of the film surface was analyzed. Films on a glass substrate with a smooth surface on Al2O3 - inhomogeneous surface structure, depending on the thickness of the film. The features of the crystal structure, magnetic phase transitions and, associated with them, the electrical and magnetic properties of bulk and film samples of Fe-Mn-Ga were investigated. Alloys Fe-Mn-Ga phase consisting of L21 and L12, the magnetic properties of the alloy due to the properties of both phases.The magnetic tunnel junctions based on Fe-Mn-Ga alloy were manufactured and studied. Obtained values of tunnel magnetoresistance 4 - 20% open the perspectives of their practical applications as magnetic sensors.