Patent ID: 8535867

Claim:
A ferrite core material for an electrophotographic developer, the ferrite core material having a ferrite particle composition represented by the formula (1) shown below, containing SrO replacing a part of (MnO) and/or (MgO) in the formula (1) shown below, having a Cl concentration of 0.1 to 100 ppm, as measured by an elution method of the ferrite core material, and having strontium ferrite and Sr—Fe compounds, wherein the proportion of the strontium ferrite in the whole of Sr—Fe compounds contained in the ferrite particle is in the range shown in the formula 2 below: (MnO) x (MgO) y (Fe 2 O 3 ) z (1) wherein x=35 to 45 mol %, y=5 to 15 mol %, z=40 to 60 mol %, and x+y+z=100 mol %; 0 ≦A /( A+B )≦0.8 (2) wherein A is the content (% by weight) of the strontium ferrite and B is the content (% by weight) of the Sr—Fe compounds.