  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 ^\circ 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.
