Magnetic sensor device

A magnetic sensor device for sensing and distinguishing between different types of detection objects including at least a first sheet-like detection object that includes a first magnetic body having a first coercivity and a second sheet-like detection object that includes a second magnetic body having a second coercivity that is larger than the first coercivity, the magnetic sensor device composing:

• a magnetizing magnet configured to generate a magnetization magnetic field in a transport plane and separately magnetize the detection objects, wherein a magnitude of a magnetic field component parallel to the transport plane in the transport plane of the magnetization magnetic field being larger than or equal to a saturation magnetic field of the second magnetic body having the second coercivity and larger than a saturation magnetic field of the first magnetic body having the first coercivity;
• a bias magnet configured to generate a bias magnetic field having a magnetic force direction of a center of a magnetic flux that intersects a plane of the detection object magnetized by the magnetizing magnet transported along the transport plane, wherein a magnitude of a magnetic field component parallel to the plane of the detection object in the bias magnetic field occurring in the plane of the detection object is larger than the first coercivity and less than the second coercivity;
• and
• a magnetoresistive effect demon disposed at the bias magnet and facing the plane of the detection object,
• wherein the bias magnetic field has, in a plane parallel to the transport plane, (i) a positive-direction component magnetic field that is directed in the same direction as a transport direction in which the detection object is transported, and (ii) a negative-direction component magnetic field that is directed opposite to the transport direction, and
• upon the detection object passing through the bias magnetic field, (i) when the detection object is the first sheet-like detection object that includes the first magnetic body having the first coercivity, the bias magnet is configured to reverse a direction of magnetization of foe first magnetic body, and (ii) when the detection object is foe second sheet-like detection object that includes the second magnetic body having the second coercivity, the bias magnet is configured to maintain a direction of magnetization of the second magnetic body the same as that of magnetization of the second magnetic body by the magnetizing magnet.