Properties Of Ferromagnetic Shape Memory Alloy Ni-Mn-Ga Thin Films Prepared By Magnetron Sputtering Deposition

Ferromagnetic Shape Memory Alloys(FSMAs) is a new type of intelligent material.Their notable character is shape memory effect which can be induced by magnetic field,and their martensite has large reversible magnetic-field-induced strain. However,the bulk has very high brittleness and low response speed,it is difficult to be machined to small parts,which restrain its application in certain extent.Recently, people developed the films of ferromagnetic shape memory alloys,which is a good solution to deal with this problem.In this text,Ni-Mn-Ga thin films were prepared by MW-ECR RF magnetron sputtering on Si substrate,Ni-Mn-Ga substrate and PbZrTiO₃(PZT) piezoelectric ceramics substrate.And then,the effect of preparation parameters on the composition of films and property were discussed.The results are given as below:The films were characterized with energy dispersive spectroscopy(EDS),the results show that sputtering power can affect the composition of the films.When the sputtering power is between 175W and 200W,the composition of the films is similar to the composition of target.With the increase of the sputtering power,Mn and Ni content increase slightly in the film,while the Ga content decreased in the film.However,when the films were deposited on the Ni-Mn-Ga substrate and the PZT substrate,the lapse rate of the Ga content in the film is large,which indicated that the different matrix material has obvious influence on the composites of the thin film.Then the films were annealed in vacuum sintering furnace.The heat treatment temperature is in the range of 500-900℃.By XRD analysis,the deposition thin films are amorphous and the annealed films are polycrystal with main grain orientation(022)(004).The size of grain presents the linear trend that rises as the increase of the heat treatment temperature.The flims were characterized with scanning electron microscopy(SEM),the result shows that the substrates can affect growth of the film.The surfaces of the films deposited on silicon substrate are much smoother than that of the films deposited on PZT or Ni-Mn-Ga substrate.Some particles existed in the surface of the film and the largest diameter of the particle is about 2μm.The cross-sectional SEM image of the thin film deposited on the PZT substrate show that the Ni-Mn-Ga cylindrical grains grow with a preferential orientation normal to substrates.The thickness of the film is about 5μm.By WYKO analysis,the surface roughness of the films increases with the sputtering power increases.By nanometer sclerometer(Tribolndenter) system and friction force microscope(LFM) analysis,as the annealing temperature rises,its surface hardness and elastic modulus increase.By atomic force microscope(AFM) analysis, the growth of the films belong to the model nuclear,and described its growth process.The strain and magnetic field intensity curve shows that the strain grows with the increase of magnetic field intensity.When the field is about 4.0KOe,the largest strain of heated films on Si substrates and Ni-Mn-Ga substrate are -85ppm and -142ppm respectively,the largest strain of unheated films on Si substrate is -80ppm.