A multi-channel magnetoresistance effect type magnetic head has a short wavelength region magnetic head element and a relatively longer wavelength region magnetic head element. The two head elements are provided on a magnetic substrate with each having a magnetic circuit containing a magnetic gap facing a surface adjacent to and across from a magnetic recording medium. Each magnetic circuit has a discontinuity portion with a bridging magnetoresistance effect sensing element to magnetically connect the discontinuity portion. The longer wavelength magnetic head discontinuity portion is spaced at a greater distance from the adjacent surface than is the discontinuity portion of the shorter wavelength magnetic head element.

A magnetic transducer and method of operation is disclosed for removing the effect of interference magnetic fields present when detecting information magnetically coded on a carrier. The transducer is provided with a magnetoresistive compensating element disposed to develop a voltage in response to the interference magnetic fields equal to that developed across a magnetoresistive detecting element; however, the compensating element is positioned out of the magnetic leakage field of the coded information.

A reader for a magnetically coded card with a magnetodiode as the magnetic field sensor. A circuit for compensating for changes in magnetodiode resistance due to ambient temperature change. First and second amplifiers connected in a self balancing nulling system and having the magnetodiode signal as an input, and providing a null output signal for no magnetic field at the diode, with third and fourth amplifiers connected as comparitors and providing high and low output signals for magnetic fields of opposite polarity.

A magnetic detection apparatus for use in an encoder includes a first magnetic sensor for detecting an external magnetic field and a second magnetic sensor for detecting a signal magnetic field. The first magnetic sensor is constructed by two magnetoresistive elements and a conductive layer arranged therebetween for applying a magnetic bias thereto. The second magnetic sensor is constructed by two magnetoresistive elements, first conductive layer arranged therebetween for applying a magnetic bias thereto and second conductive layer arranged on one side of two magnetoresistive elements for canceling an effect of the external magnetic field by feeding back a differential output derived from the first magnetic sensor thereto. In such a construction, it is possible to derive from the second magnetic sensor only a signal representing the signal magnetic field without being affected by the external magnetic field.

An electromagnetic transducer particularly of the magneto-resistive (MR) type is biased by an inductive circuit means and operates within the linear portion of its characteristic curve. The inductive circuit means is interconnected to the output terminals of said transducer. An amplifier means is connected to the output terminals of the transducer and the inductive circuit means. The amplifier means is also biased by the inductive circuit means. The biasing scheme is enhanced when a gyrator is used as the inductive circuit means.