| Co-based nanocrystalline film was widely used in high-frequency soft magnetic recording and perpendicular magnetic recording as the reason of high saturation magnetization and easy to obtained perpendicular magnetic anisotropy of Co-based alloys. The Co-based nanocrystalline films were prepared by electrodeposition method because it is both economical and effective. Furthermore, the properties of films expected to be better with nanostructure and the nanocrystalline films can be prepared through controlling the electrodeposition bath and electrical parameters (pulse-electrodeposition). In general, the electrodeposited films were annealed to form chemical order and relieve stress which caused by the non-equilibrium state of electro-crystallization. However, the traditional heat treatment always leads to the abnormal growth of crystals which will destroy the excellent properties of nano-materials. In order to control the grain growth more rational, kinds of external field had been applied during thermal annealing by many researchers. In recent years, thermal annealing under the non-contact magnetic field was reported as a promising method to control the crystal growth during recrystallization and to improve the microstructure and magnetic property at the same time. However, those research always under a weak magnetic field (B<1T), the effects of magnetic field were not very significant because of thermal disturbance. In order to make the obtained conclusions more confident, an indeep analysis was in need for the present results and this analysis need to be expanded under high magnetic fields.As the reasons mentioned above, the high magnetic fields with different strength were applied during thermal annealing of electrodeposited Co-based films in this paper. The aim of this paper is to investigate the effect of magnetic annealing on the microstructure and properties of electrodeposited Co-based films. FE-SEM was used to detect the evolution of surface morphology. More details about grain size and roughness of films were quantitatively analyzed by AFM (Nova). For the characterization of the crystal structure of the films, XRD measurements were performed. The mechanical properties of the films, such as Nano-hardness and Young’s modulus were measured by Nano-indentation method. The magnetic properties of the samples before and after annealing with and without high magnetic fields were investigated by using VSM. The results of this paper were shown below:(1) for the case of magnetic annealing monometal Co films:when applying the magnetic field during thermal annealing, the particle boundary became clear. Besides, the particle size and roughness of films were decreased.(2) for the case of magnetic annealing CoNiP films electrodeposited with unidirectional pulse: the particle size and roughness of films were increased when annealing under field of6T compared with the films annealing without magnetic field. However, when the intensity of magnetic field increased above6T, the particle size and roughness were decreased. The minimum particle size and roughness were obtained under the magnetic field of9T. The content of ε-Co alloy (hcp) increased with magnetic field strength increasing. Meanwhile, the diffraction of fcc-Ni (111) was found when annealed under magnetic field of9T.(3) for the case of magnetic annealing CoNiP films electrodeposited with bidirectional pulse: two kinds of typical surface morphology were found after annealing, one is intestine-like at field of6T and the other is pea-like at filed of OT and12T. The preferred orientation of films was (111) at field of OT and6T but change to (220) at12T. The hardness of films increased with the increase of magnetic field strength. Nonetheless, the Young modulus of the films was decrease to the minimum under the magnetic field of6T and then increased to the maximum under the magnetic field of12T. When the magnetic field was applied during thermal annealing, the saturation magnetization decreased but coercivity increased with the increase of magnetic field strength. When the film was annealed under an external magnetic field of6T, the coercivity field reached maximum and the saturation magnetization falls to minimum.In conclusion, the magnetic thermal annealing was found as an effective method to control the microstructure and properties of Co-based nanocrystalline films in this paper. The effect of magnetic field strength was non-liner for the films with different composition and process. Therefore, many kinds of films must be investigated to research the universal law of magneticfield and to obtain the best magnetic field parameters which can produce excellent comprehensive performance. All of the works mentioned above will expand the application of magnetic field thermal annealing method on micromachining. |
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