Temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites

The temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites was investigated. Co²⁺ ions are known to lead to a compensation of the magneto-crystalline anisotropy in Ni-Zn ferrites, at a temperature depending on the cobalt content and the Ni/Zn ratio. We observed similar behaviour in Ni-Zn-Cu and it was found that the core loss goes through a minimum around this magneto-crystalline anisotropy compensation. Moreover, the anisotropy induced by the cobalt allowed a strong decrease of core loss, a ferrite having a core loss of 350 mW/cm³ at 80 °C was then developed (measured at 1.5 MHz and 25 mT). This result represents an improvement of a factor 4 compared to the state of art Ni-Zn ferrites.