Apparatus for measuring magnetic field of microwave-assisted head
A measuring circuit system in a magnetic field measuring apparatus of the invention 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 SIN 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. With such a configuration, an in-plane high-frequency magnetic field generated by a microwave-assisted magnetic head is reliably and precisely measured.
1. 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 SIN 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.
2. The magnetic field measuring apparatus of claim 1 , wherein
the amplifier in the measuring circuit system is configured with a pre-amplifier and a main amplifier connected in sequence.
3. The magnetic field measuring apparatus of claim 1 , wherein
the amplifier in the measuring circuit system is a main amplifier.
4. The magnetic field measuring apparatus of claim 1 , wherein
a comparator is connected next to the narrow range band-pass filter in the measuring circuit system.
5. The magnetic field measuring apparatus of claim 1 , wherein
a low-pass filter and a comparator are connected in sequence next to the narrow-range band-pass filter in the measuring circuit system.
6. The magnetic field measuring apparatus of claim 1 , wherein
the magnetic sensor mounted on the stage is positioned facing an air bearing surface (ABS) of the microwave-assisted magnetic head anchored by the anchoring mechanism, and
the stage is moved so that the magnetic sensor scans a predetermined region of the ABS, and that the in-plane high-frequency magnetic field intensity generated by the microwave generation mechanism equipped with the microwave-assisted magnetic head is measured by this magnetic sensor.
7. The magnetic field measuring apparatus of claim 1 , wherein
the TMR element has a lamination layer structure with a barrier layer interposed between two magnetic layers.
8. The magnetic field measuring apparatus of claim 1 , wherein
the microwave-assisted magnetic head that is the target of measurement provides a main magnetic pole and an auxiliary magnetic pole, and
a main coil for generating a perpendicular recording magnetic field is provided with the main magnetic pole, and
a supplementary coil for driving an alternating current in the microwave band is provided in a gap formed with the main magnetic pole and the auxiliary magnetic pole and/or in the vicinity thereof.
9. The magnetic field measuring apparatus of claim 8 , wherein
an in-plane alternating magnetic field is generated by driving the alternating current in the microwave band to the supplementary coil of the microwave-assisted magnetic head, and
a frequency of the alternating current is substantially the same as a ferromagnetic resonant frequency of a recording layer of a magnetic recording medium that is a target of recording, and
the frequency of the alternating current is in a range of 10 GHz to 40 GHz.