Study On Preparation And Martensitic Transformation And Magnetic Properties Of Ni-Mn-Sn Alloy Thin Film

In this thesis,Ni-Mn-Sn magnetic shape memory alloy thin films have been fabricated by using magnetron sputtering technique.The results clarify the influence of sputtering parameters on chemical compositions,surface morphology,film thickness and microstructures of the thin films by using X-ray diffraction analysis,atomic force microscopy and step profiler measurement.In addition,the mechanism of effect of Co doping on magnetic properties of Ni-Mn-Sn has been revealed by first-principles calculation.The change of martensitic phase transformation and magnetic properties of Ni-Mn-Sn under pressure has been illustrated and its physical nature has been clarified as well.The results show that as the sputtering power increases,the Ni content in the Ni-Mn-Sn alloy thin film decreases but the Mn content increases and the Sn content increases slightly.When the work pressure of Ar increases,the Ni content in the Ni-Mn-Sn thin film decrease slightly and the Sn content increase slightly and smaller change of the Mn content.The sputtering yield of Ni,Mn and Sn elements are less affected by substrate temperature.The surface roughness of thin film increases with increasing Ar working pressure or sputtering power.In addition,the thickness of Ni-Mn-Sn films linearly increased with sputtering power and sputtering time.The changes of Ar working pressure or substrate temperature have little effect on the thickness of the film.It is found that the broadened XRD diffraction peaks of the Ni-Mn-Sn alloy film fabricated at a substrate temperature of room temperature indicate that the film exhibits high degree of disorder with only partially crystalline state.The XRD characteristic diffraction peaks of the thin film which substrate is heated to 823 K fabricated become narrower and its characteristic diffraction intensity increased.It shows that using a method of heating the substrate the Ni-Mn-Sn films with well crystallized and high degree of ordering can be fabricated.The results also indicate that Co doping has a significant influence on the magnetic configuration and magnetic properties of Ni-Mn-Sn.The doping of Co change Mn-Mn interaction in Ni-Mn-Sn alloy from anti-ferromagnetism to ferromagnetism.Effect of Co doping on Ni-Mn-Sn magnetic exchange interaction directly change its magnetic moment.The saturation magnetization of Co doped Ni-Mn-Sn parent phase linearly increases with increasing Mn content.Moreover,the physical nature of increasing total magnetic moments by Co doping has been clarified based on the electronic structure.The calculated results show that the total magnetic moments of Ni-Mn-Sn parent phase linearly decrease with pressure increases.This change is due to the decrease of lattice constant under pressure and the increasing width of energy band.As the pressure increased,total energy difference of the paramagnetic state and the ferromagnetic state of Ni-Mn-Sn parent phase decrease and the Curie temperature decreases as well.The studies also indicate that increasing the pressure can make Ni-Mn-Sn martensite more stable relative to the parent phase.Therefore,the increase of martensitic transformation temperature is due to enhancement of the hybrid between Mn 3d state and Ni 3d state under pressure.