Patent ID: 7172846

Claim:
A carrier, comprising: a manganese ferrite core material; and a layer located on a surface of the manganese ferrite core material, wherein the carrier satisfies the following conditions: 0.1â‰¦ Kâ‰¦ 30, where K=(S/M)Ã—100, S and M represent, respectively, a standard deviation and an average of the expression M 2 /(M 1 +M 2 ), wherein said average ranges from 0.05 to 0.45, and where M 1 and M 2 represent, respectively, a content of iron and a content of manganese in a carrier particle determined by a method comprising: magnetically holding the carrier on a cylindrical sleeve having a magnetic pole area located over a magnetic pole having a peak magnetic flux density of about 100 mT in a direction perpendicular to a rotational axis of the cylindrical sleeve; rotating the cylindrical sleeve around the rotational axis for 30 min; and removing the carrier from the magnetic pole area by applying a force in said direction, said force being approximately equal to three times as much as a gravitational weight of the carrier; a magnetization ranging from approximately 45 to 75 emu/g at 1,000 Oe; a mass-averaged particle diameter, D 4 , between 25 and 65 Î¼m, wherein carrier particles having a particle diameter not greater than 12 Î¼m are included in an amount not greater than 0.3% by weight; and a ratio D 4 /D 1 is between 1 and 1.3, where D 1 is a number-averaged particle diameter of the carrier.