Patent ID: 7183033

Claim:
A carrier core material for an electrophotographic developing agent, comprising ferrite particles containing a ferrite component represented by the following formula (A): (MnO) x (MgO) y (Fe 2 O 3 ) z (A) wherein x, y and z are each expressed in % by mol and are numbers satisfying the conditions of 40≦x≦60, 0.1≦y≦10 and x+y+z=100, and ZrO 2 in an amount of 0.01 to 5.0 parts by weight based on 100 parts by weight of the ferrite component, said ZrO 2 not forming a solid solution with the ferrite component and said ZrO 2 is finely dispersed in the ferrite component, wherein the carrier core material has a magnetization, at 1000(10 3 /4π·A/m), of 65 to 85 Am 2 /kg and an electrical resistance, at an applied voltage of 1000 V, of 10 5 to 10 9 Ω.