Effect Of Co - Doped On The Properties Of Ni - Mn - Ga Alloy Films

Ni-Mn-Ga shape memory alloy film is becoming more and more popular of all the magnetic materials in MEMS field. As Ni-Mn-Ga film is easier to be processed than bulk materials, and it has big magnetically induced strain and high frequency response. In order to obtain better properties of Ni-Mn-Ga films, people improved the preparation process, chemical composition and other conditions to optimize its property. At present, doping is one manner to improve the properties of Ni-Mn-Ga thin films. At the same time, Co-doping has a great influence on properties of Ni-Mn-Ga films.Ni-Mn-Ga-Co thin films were prepared by radio-frequency magnetron sputtering. By controlling the heat treatment temperature and the sputtering time we prepared different Ni-Mn-Ga-Co films.The results indicated that small amount of Co-doped have a great impact on the films. The grain size of the Ni-Mn-Ga-Co films surface become small, the grains refined obviously. The surface roughness of the films become large. Films doped with Co are easy to be magnetized. Large applied magnetic field can make them to reach saturation. At the same time, the coercive force and the Curie temperature is also decreased. When the test temperature changes, Undoped films did not occur martensitic transformation.Sputtering time have a significant effect on the properties of Ni-Mn-Ga-Co thin films. The particle size of the film surface gradually becomes smaller and the saturation magnetization increases when the sputtering time increases. When the sputtering time was 60 min, saturation magnetization reaches a maximum. When the sputtering time is 20 minutes,remanence and coercivity become low. The curie temperature of Ni-Mn-Ga-Co film rises when the sputtering time gradually increases. The curie temperature of the film is 355 K when the sputtering time is 60 min. This film has the best magnetic properties.Annealing temperature has a significant effect on the performance of Ni-Mn-Ga-Co thin films. When the Ni-Mn-Ga-Co thin films annealed at 1073 K, the film has the largest saturation magnetization. When the annealing temperature increases or decreases, the magnetic properties of the film become worse.