The miniaturization of the bit size of a record medium is promoted according to the enhancement of the recording density of a hard disk drive (HDD). However, as the miniaturization of the bit size is advanced, the extinction by thermal fluctuation of a recorded state is feared. To settle such a problem and to stably maintain a bit in future high density recording, it is required to use a record medium the coercive force of which is large (that is, the magnetic anisotropy of which is large). However, a strong recording magnetic field is required to record on the record medium the coercive force of which is large. Actually, the enhancement of the strength of the recording magnetic field is limited because of narrowing the width of a recording head and the limitation of available magnetic materials. For such a reason, the coercive force of the record medium is limited by the dimension of a recording magnetic field that can be generated by the recording head. As described above, to correspond to incompatible requests for the high thermal stability of the medium and the coercive force that is easy to record, a recording method of effectively reducing the coercive force of a record medium only in recording using various auxiliary means is devised and heat-assisted recording in which recording is made using a magnetic head and heating means such as a laser together is its representative.
In the meantime, a method of locally reducing the coercive force of a record medium by using a recording magnetic field from a recording head and a high-frequency field together and recording also exists. For example, JP-A No. 1994-243527 discloses technique for recording information by heating a magnetic record medium by Joule heating or magnetic resonance by a high-frequency field and locally reducing the coercive force of the medium. In such a recording method (hereinafter called microwave assisted recording) of utilizing magnetic resonance between a high-frequency field and a magnetic field applied by a magnetic head, a large high-frequency field proportional to an anisotropy field of a medium is required to be applied so as to acquire the effect of reducing an inverted magnetic field because magnetic resonance is utilized.
Recently, a principle for generating a high-frequency field using spin torque as in a spin-torque oscillator is proposed and the possibility of microwave assisted recording is being realized. For example, “Bias-Field-Free Microwave Oscillator Driven by Perpendicularly Polarized Spin Current” written by X. Zhu and J. G. Zhu, IEEE TRANSACTIONS ON MAGNETICS, P2670, VOL. 42, NO. 10 (2006) discloses results of the calculation of a spin-torque oscillator that oscillates without a biased magnetic field from an external device. Further, in “Microwave Assisted Magnetic Recording” written by J. G. Zhu and X. Zhu, the Magnetic Recording Conference (TMRC) 2007 Paper B6 (2007) discloses technique for recording information on a magnetic record medium the magnetic anisotropy of which is large by arranging a field generation layer (FGL) the magnetization in which is spun at high speed by spin torque next to a main pole of a perpendicular magnetic head and in the vicinity of the magnetic record medium and generating a microwave (a high-frequency field). Further, “Microwave Assisted Magnetic Recording with Circular AC Field Generated by Spin Torque Transfer” written by J. Zhu and Y. Wang, MMM Conference 2008 Paper GA-02 (2008) presents a spin-torque oscillator that controls a rotation direction of FGL utilizing a magnetic field of a main pole close to the FGL and it is described that hereby, microwave assisted magnetic reversal of a medium can be efficiently realized.