Abstract: The invention provides a manganese-zinc ferrite production process comprising a maximum temperature holding step for firing and a cooling step in a nitrogen atmosphere. The nitrogen atmosphere changeover temperature T in the cooling step is below 1,1500° C. and equal to or higher than 1,0000° C., and the cooling rate V1 conforms to the condition defined by: T≦(V1+1,450)/1.5  (1) Here T is the nitrogen atmosphere changeover temperature in ° C. and V1 is the cooling rate in ° C./hour from T down to 900° C.

Abstract: A ferrite core is provided. This ferrite core has high saturation flux density Bs at a high temperature of 100° C. or higher, and in particular, at around 150° C., and has excellent magnetic stability at a high temperature, experiencing reduced deterioration of magnetic properties, and in particular, reduced core loss at such high temperature (even by trading off some improvement in the level of the loss).

Abstract: MnZn ferrite comprises a main component comprising iron oxide 52.5 to 54.0 mol % in terms of Fe2O3, zinc oxide 7.7 to 10.8 mol % in terms of ZnO, and manganese oxide of the remaining, and sub-components of silicon oxide 60 to 140 ppm in terms of SiO2 and calcium oxide 350 to 700 ppm in terms of CaO, and further contains nickel oxide 4500 ppm or lower (not including 0) in terms of NiO.

Abstract: The invention provides a manganese-zinc ferrite production process comprising a maximum temperature holding step for firing and a cooling step in a nitrogen atmosphere. The nitrogen atmosphere changeover temperature T in the cooling step is below 1,1500° C. and equal to or higher than 1,0000° C.

Abstract: A ferrite having low power losses, high .DELTA.B=Bm-Br at high frequency, and improved .mu.a-B properties is provided as well as a core for a power supply using the same. The ferrite contains 30-41 mol % of MnO, 6-16 mol % of ZnO, and the balance of Fe.sub.2 O.sub.3 as main components and 50-250 ppm of SiO.sub.2, 200-1500 ppm of CaO, up to 4000 ppm of SnO.sub.2, up to 3000 ppm of TiO.sub.2, at least 300 ppm of SnO.sub.2 +TiO.sub.2, from more than 0 to 500 ppm of Nb.sub.2 O.sub.5, and from more than 0 to 400 ppm of ZrO.sub.2 as subordinate components.