Konopliuk S. Magnetic and structural transitions in shape memory Heusler alloys

This work considers relationship between structural and magnetic transitions in Heusler alloys and influence of external parameters such as temperature, magnetic field and mechanical stress on their crystalline structure, magnetic, transport and caloric properties. The temperature hysteresis of ferro- to paramagnetic transition was observed in an alloy of Ni-Mn-Ga system. The reasons behind hysteretic behavior of magnetic transition were established. The direct adiabatic changes of temperature in magnetic field were determined for several most prospective Heusler alloys - Ni-Mn-Ga, Ni-Mn-Sb-Fe, Ni-Mn-In. Ni-Mn-In. The investigation of stress-strain behaviour of Ni-Mn-In alloys revealed superelastic effect and considerable change of electric resistance under compressive stress. The latter presents Ni-Mn-In alloys as appropriate candidates for applications as sensors responding to mechanical stress. The study of magnetotransport properties of nanogranular Cu-Mn-Al alloys has shown that different mechanisms of magnetizing are realized in the system of ferromagnetic Cu2MnAl nanoparticles: individual one when interparticle correlations are absent and collective one when they are present. Analysis of optical spectra and Seebeck effect allowed to establish that martensitic transformation in Cu-Mn-Al is accompanied by a change in the Fermi energy, decrease in the plasma frequency and growth of the relaxation frequency of conduction electrons.