Structural and magnetic properties of nanostructured Ni0.5Zn0.5Fe2O4 films fabricated by thermal spray

Nanostructured Ni0.5Zn0.5Fe2O4 thick films were fabricated by a high velocity oxygen fuel (HVOF) thermal spray approach with over 98% of the theoretical density and with no cracks, followed by heat treatment under an oxygen atmosphere. Crystallographic, microstructural, as well as static and dynamic magnetic properties of the films were studied by x-ray diffraction, high-resolution transmission electron microscopy, superconducting quantum interference device magnetometer, and high-frequency impedance analyzer. By controlling the nature of the flame, the crystal structure of the ferrite can be retained during thermal spraying while the grain size as small as 10-20 nm can be attained. By controlling the spray conditions and postannealing, the real part of initial complex permeability mu' reaches 120 while the image part mu" remains small in the frequency range up to 13 MHz. In comparison with a conventional Ni0.5Zn0.5Fe2O4 (mu'=800, cutoff frequency f(c)=1.5 MHz), a nanostructured sample possesses a much higher cutoff frequency, a merit for high-frequency application. It is determined that HVOF is a promising approach for the fabrication of nanostructured ferrite films. (C) 2003 American Institute of Physics.