In-plane magnetic anisotropy induced in spin-sprayed Ni-Zn-Co ferrite films exhibiting strong magnetic loss at gigahertz range

Ni-Zn(-Co) ferrite films of 0.5-0.6 μm in thickness were deposited on glass substrates by the spin-sprayed ferrite plating at as low as 90°C applying external magnetic field of 50 Oe. Under no bias field, while the film without Co substitution (Ni_0.21Zn_0.27Fe_2.52O₄) exhibited a relatively high coercivity H_c of about 27 Oe, it decreased to 15 Oe for Co substituted film (Ni_0.21Zn_0.27Co_0.04Fe_2.48O₄), and a slight uniaxial anisotropy was induced along the liquid flow direction of sprayed solutions. The decrease in H_c was attributed to the anisotropy compensation originated by Fe²⁺ and Co²⁺. Under bias field of 50 Oe, a definite in-plane magnetic anisotropy was induced in the Co substituted film. The imaginary permeability μ´´ was greater than 20 over a wide frequency range from 300 MHz to 3 GHz. Since the product of μ´´×f, which is proportional to the absorption of conducted noise, increased even in gigahertz range reaching the peak at 1.7 GHz, Ni-Zn-Co ferrite films with in-plane uniaxial anisotropy are applicable as shielding materials for suppressing electromagnetic interference in gigahertz range.