High Temperature Measurement of Complex Permittivity and Permeability of Fe3O4 Powders in the Frequency Range of 0.2 to 13.5 GHz

The real and imaginary parts of relative permittivity (εr′ and εr″) and permeability (μr′ and μr″) of Fe3O4 powder were successfully measured over the temperature range of 25–575°C by means of the coaxial transmission line method in order to elucidate the heating behaviours of Fe3O4 powder. The measurement frequency range is from 0.2 to 13.5 GHz. With respect to the temperature dependencies of the complex permittivity, the εr′ values show a peak around 450–500°C. The εr″ values monotonically increase with increasing temperature, in particular, showing abrupt increase above ca. 400°C. As for the complex permeability, the μr′ values decrease with an increase in temperature, and reach the same level as that of vacuum (μr′=1) at 575°C, i.e., the maximum measurement temperature. The μr″ values increase with temperature until 500°C below 3.5 GHz although they monotonically decrease with an increase in temperature above 3.5 GHz.