Patent ID: 8680855

Claim:
A magnetic field measuring apparatus for measuring an in-plane high-frequency magnetic field intensity that is generated from a microwave generation mechanism equipped with a microwave-assisted magnetic head, the measuring apparatus comprising: an anchoring mechanism for anchoring the microwave-assisted magnetic head that is a target of measurement; a high-frequency current driving system for applying a high-frequency current to the microwave generation mechanism equipped with the microwave-assisted magnetic head; a magnetic sensor having a tunneling magnetoresistive (TMR) element for measuring the in-plane high-frequency magnetic field intensity generated from the microwave generation mechanism; a measuring circuit system connected to the magnetic sensor; and a stage capable of moving in three dimensional directions on which the magnetic sensor is mounted, wherein the measuring circuit system has an amplifier and a band-pass filter connected in sequence on an output terminal side of the TMR element, the band-pass filter is a narrow-range band-pass filter such that a peak pass frequency of the filter that is a center is a basic frequency selected from a range of 10 to 40 GHz and a band width centered around the basic frequency is a narrow range of ±0.5 to ±4 GHz; and with the measuring circuit system, an S/N ratio (SNR) of 3 dB or greater is obtained, the SNR being defined by a ratio of an amplitude S of a high-frequency generated signal induced by the TMR element to a total noise N that is a sum of a head noise generated by the TMR element and a circuit noise generated by the amplifier, the microwave-assisted magnetic head that is the target of measurement provides a main magnetic pole and an auxiliary magnetic pole, a main coil for generating a perpendicular recording magnetic field is provided with the main magnetic pole, and a spin torque oscillator is provided in a gap formed with the main magnetic pole and the auxiliary magnetic pole and/or in the vicinity thereof, the spin torque oscillator being configured with multiple magnetic thin films for generating an alternating current in the microwave band.