Electrochemical Preparation Of Cobalt-based Hard Magnetic Film And Performance

Cobalt base magnetic films play an important role in the modern high technological magnetic materials. Therein, the CoP series hard magnetic films attract great attentions due to their excellent hard magnetic properties. Among the preparation method of the CoP series hard magnetic films, the electrochemical method has great developmental potential in that it can deposit on large-scale complex surface in low temperature. However, due to the complex composition of plating bath, there are many factors which influence the magnetic properties of the film. To make clear the factors which influence the magnetic properties of the film and their order, in this thesis, the CoP series hard magnetic films were prepared by electroless plating and electrodeposition, respectively. The effect of the factors in deposit process on structure and magnetic properties were studied in detail. The relation of deposit process-structure-magnetic properties is gotten. Base on that, BaFe₁₂O₁₉ particles were incorporated in the film by composite electrodeposition which improves the hard magnetic properties further. The magnetic composite electrodeposition offers a new convenient way to prepare the hard magnetic film.The main content of the thesis list as following:1. The CoNiP alloy film was prepared by electroless plating. The optimize process and the main factors which influence the magnetic properties of the film were gotten by L₁₆₄₅ orthogonality experiment. It is found that the order of the factors is: the buffer concentration > the reduce agent concentration > the ratio of [Co²⁺ ]/[Ni²⁺ ] > pH > plating time.2. The effects of the buffer concentration and the reduce agent concentration on structure and magnetic properties were studied in detail. The result shows that the coercivity of the film is high when the film structure is the fcc β-Co solid solution. In a range, the finer the grain size is, the higher the coercivity is. Whereas the structure changes to the hcp α-Co solid solution, the coercivity declines.3. The effect of heat treatment of CoNiP alloy film was carried out. The result shows that the coercivity increases after heat treatment. When the treatment temperature between 100～350℃, two phases coexist and the grain size of β-Co grows up, which lead to theincreases of coercivity. When the treatment temperature comes 400℃ or even higher, the coercivity declines.4. The CoNiP alloy films were prepared by galvanostatic electrodoposition and potentiostatic electrodoposition. The deposition process was optimized. The result shows that the coercivity of the film is close to that prepared by electroless plating.5. The CoNiP-BaFe₁₂O₁₉ composite film was prepared by magnetic composite electrodeposition which uses controlled potential coulometry in CoNiP bath containing BaFe₁₂O₁₉ particles. The result shows the incorporation of BaFe₁₂O₁₉ particles enhanced the coercivity and squareness ratio dramatically.