Novel Ni–Mn–Co ferrite for gigahertz chip devices.

The effect of Mn and/or Co doping in Ni–Mn–Co ferrite on the static, dynamic magnetic properties, and thermal magnetic stability were investigated for high frequency microwave applications up to the gigahertz range. Saturation magnetization and coercivity increased with increased substitution of Mn and Co, respectively. Both Mn and Co substituted Ni–Mn–Co ferrite exhibited higher thermal stability factor rather than Ni–Mn and Ni–Co ferrites. The highest thermal stability factor was achieved to be -12.0×10^-4 °C/ppm for Ni_0.93Mn_0.05Co_0.02Fe₂O₄. The second highest, -11.88×10^-4 °C/ppm, was measured for Ni_0.7Mn_0.05Co_0.02Fe_2.23O₄. Permeability (μ), permittivity ([variant_greek_epsilon]), and cutoff frequency of Ni_0.93Mn_0.05Co_0.02Fe₂O₄ and Ni_0.7Mn_0.05Co_0.02Fe_2.23O₄ showed 7.41, 4.56, 1084 MHz, and 3.87, 4.55, 1436 MHz, respectively. Furthermore, the μ/[variant_greek_epsilon] ratio of Ni_0.93Mn_0.05Co_0.02Fe₂O₄ was found to be 1.63 (μ/[variant_greek_epsilon]=7.41/4.56). [ABSTRACT FROM AUTHOR]