Microstructure and Magnetic Anisotropy of Electro-Deposited FeCo Thin Films

FeCo films with various Fe/Co atomic ratios were deposited by electro-plating method. Microstructure, static magnetic properties and microwave permeability of as-deposited films were examined. FeCo films deposited from solution with an Fe²⁺/Co²⁺ mole ratio of 0.7:1 exhibited almost in-plane isotropy and a large coercivity Hc of about 100 Oe. With the increase in Fe²⁺ /Co²⁺ ratio and ions concentration in plating solution, the deposited films showed lower coercivity and well-defined in-plane anisotropy. For the film deposited from solution with an Fe²⁺/Co²⁺ mole ratio of 3:1 and total depositing ion ( Fe²⁺ and Co²⁺) concentration of 480 mmol/l, the ferromagnetic resonance frequency (f_r) corresponding to the maximum imaginary permeability (μ"_max) is around 1 GHz, and the static initial permeability (μ\´₀) is about 265. The formation of in-plane anisotropy and reduction of coercivity originates from the modification of the film microstructure and composition, which can be well understood by the random anisotropy theory. These soft FeCo films with in-plane anisotropy are promising for high-frequency applications in gigahertz due to their excellent microwave properties.