Investigation of magnetic field induced martensitic phase transformation in shape memory Ni-X-Mn-Sn-B (X=Fe, Co ve Cu) ribbons

In this thesis, magnetic field-induced-shape memory properties of the alloys with nominal composition of Ni-X-Mn-Sn-B (X=Fe, Co, Cu) was investigated. In order to prevent the evaporation of the materials during the production process, an amount of boron, which will not cause breaking of the materials, was added to the main system. In the study, firstly the Ni-X-Mn-Sn-B (X=Fe, Co, Cu) alloys with the molar formula of Ni50Mn38Sn12+Bx, Ni50-yFeyMn38Sn12+Bx (y=1,3 and 5), Ni50-yCoyMn38Sn12+Bx (y=1,3 and 5) and Ni50-yCuyMn38Sn12+Bx (y=1,3 and 5) were fabricated in bulk form by using arc-melting technique. Then, the bulk samples were converted ribbon forms by using melt-spinning technique. Both bulk and ribbons samples were heat treated. Structural/microstructural, electrical and magnetic properties of the bulk and ribbons were analyzed by XRD, SEM-EDX, R-T, R-H, M-T and M-H. Structural/microstructural analysis showed that all the samples were converted required crystalline form. From R-T and M-T measurements, it was determined that the samples exhibited martensitic transformation. While phase transition temperatures from austenite phase to martensite phase in undoped ribbon were very close to room temperature, it was found that the phase transition temperatures decreased by doping of Fe, Co and Cu. Dopings caused a significant increase in the magnitude of magnetization. Although the ribbons exhibited a ferromagnetic behaviour at high magnetic fields, an antiferromagnetic behaviour was seen at low magnetic field due to high Mn concentration. From magnetotransport measurements carried out at temperatures inside and outside the thermal hysteresis region, resistivity of both bulk and ribbon samples varied depending on Hall Effect, Anomaly Hall Effect (AHE) and Magnetoresistivity. At martensite  austenite transition region between As and Af, the resistance curves of the samples overlapped at ~90 kOe, which is given as an evidence for oneway martensitic transition. The results showed that ferromagnetic shape memory ribbons fabricated by melt-spinning technique are very promising for magnetic sensor applications.