Y. Itoh

“Contact” solid immersion lens near-field optical recording in magneto-optical TbFeCo media

The solid immersion lens (SIL) near-field magneto-optical (MO) recording technique offers a significant increase in areal density through near-field resolution enhancement. Since the near-field recording scheme requires close proximity of the optical recording head and the magnetic medium, the SIL MO recording setup is usually changed to a “first surface” recording. This requires further optimization of the optical flying head design and a MO medium. In this work marks as small as 150 nm using a SIL with a 680 nm laser source and a TbFeCo magneto-optical medium were recorded. The minimum size of a recorded mark is strongly dependent on the slider flying height, the flying attitude, and lens centering. It should be emphasized that recording power as small as 4 mW is sufficient enough to achieve carrier-to-noise ratio of more than 30 dB.

Solid immersion lens near field optical approach for high density optical recording

High-density magneto-optical recording using near field optics with a solid immersion lens is discussed. The spot size, and defocusing distance are calculated for various combinations of n and NA. Also, the misalignment of the objective lens and SIL is discussed. The magnetic and magneto-optical properties of SIL media candidates of TbFeCo/Pt multilayers are presented.

Relaxation time and thermal stability in magneto-optical recording media

The time dependence of the magnetization process in amorphous TbFeCo thin films and (TbFeCo/Pt) multilayers is studied. By assuming a Gaussian distribution of relaxation times for magnetic aftereffect, the non-Arrhenius behavior of the magnetization decay is found in almost all samples. From a fitting of experimental data one can determine the mean value of relaxation time /spl tau//sub 0/ and also its width /spl Delta//spl tau//sub 0/. The multilayers of TbFeCo/Pt show a high stability compared to single layers of TbFeCo with also a small activation volume.

Magnetic and magneto-optical properties of TbFeCo/(Pt, Pd) multilayers optimized for short wavelength recording

Magnetic and magneto-optical properties of TbFeCo/Pt and TbFeCo/Pd multilayer films prepared by sputter deposition are discussed in conjunction with the multilayer structure. The magnetic behaviors in TbFeCo/Pt and TbFeCo/Pd multilayers are very similar to each other, and the saturation magnetization Ms at 298 K increases with thickness t of Pt and Pd up to tPt, tPd=12 A. In TbFeCo/Pt multilayers, the contribution of Pt to the polar Kerr spectra is significant at ultraviolet photon energies. The Kerr rotation θK and ellipticity ηK are enhanced with Pt layer thickness and become saturated at tPt=12 A. On the other hand, little contribution from Pd atoms is found in the TbFeCo/Pd multilayer.

EFFECT OF PT IN TBFECO ON MAGNETIC AND MAGNETO-OPTICAL PROPERTIES

The effect of Pt additives in TbFeCo(Pt)/Pt multilayers on magnetic properties and magneto-optical Kerr effect is investigated. The perpendicular magnetic anisotropy Ku of the multilayer becomes larger (∼2×106 erg/cm3) than that of the TbFeCo(Pt) single layer. Pt layers are found to contribute significantly to the polar Kerr spectra at ultraviolet photon energies beyond 4 eV. The largest enhancement in the Kerr rotation θK is found at about 5 eV. The Kerr rotation θK and ellipticity ηK are enhanced with increasing Pt layer-thickness tPt, and become saturated at tPt=12 A. This result implies that Pt atoms up to about 6 A from the interfaces are contributing to the Kerr activity.

Magnetic and magneto-optical properties in TbFeCo/(Pt, Pd) multilayers

The magnetic and magneto-optical properties of TbFeCo/(Pt, Pd) multilayer films prepared by sputter deposition are discussed in conjunction with their multilayer structure. The effect of polarized Pt on the polar Kerr spectra is significant at ultraviolet photon energies (∼5 eV). Based on the magnetic and magneto-optical properties, it is quite reasonable to surmise that an alloy is formed at the interface in real multilayers. It is the most obvious evidence that the saturation magnetization drastically increases with Pt and Pd thickness up to 12 A, which indicates that the interfacial regions are essentially due to Fe–Pt and Fe–Pd alloys. This possibility was supported by the simulation of Kerr spectrum for the proposed model based on the layered-structural analyses.

A high numerical aperture solid immersion lens magneto-optical recording system

A high numerical aperture solid immersion lens (SIL MO) magneto-optical recording system based on supersphere SIL approach is described. Effects of SIL on the recording performance of the magneto-optical system are analyzed. It is found that effective numerical aperture as high as 1.46 can be achieved using a contact SIL operation mode and evanescent coupling optimized TbFeCo recording media. A novel quadrilayer media design with CNR value of 50 dB is proposed.

Thermal Stability in Magnetic and Magneto-Optical Recording Media

First, a brief review of thermal decay of magnetization is given. Discussions on activation volume are presented in detail for longitudinal recording media. It is noted that the activation volume estimated based on waiting time methods is found to decrease with increasing reversing field for all the media under consideration. This result suggests that an activation volume in a written bit changes from place to place, depending upon on stray field due to a bit-transition. The recording noise is closely related to activation volume as well. Thermal stability of amorphous TbFeCo mono-layers and {TbFeCo/Pt} multilayers is studied by magnetic viscosity measurements M(t). Using, isothermal remanence measurements the relationship between the magnetization reversal process and its time dependence is investigated. The non-linear evolution of magnetization with In(time) takes place when the mechanism responsible for magnetization reversal process is mainly domain nucleation. On the other hand domain wall motion process induces a linear M(t) behavior. For multilayers with very small Pt thickness (samples with high square hysteresis loop), magnetization time decay can be described by a single energy barrier E B model. As Pt thickness increases, the distribution of E B becomes wider leading to almost linear magnetization decay with In(time) as in longitudinal recording media. Finally, the life time of written domains is discussed in terms of domain size. It is concluded that the difference between a pinning field and wall-field is a decisive factor for governing a life time.

High density magneto-optical recording using solid immersion lens with magnetic field modulation

A near field optical technique based on combined supersphere solid immersion lens (SIL) with magnetic field modulation (MFM) recording is described. A better resolution is achieved by using SIL with MFM recording in comparison with light intensity modulation. A recorded mark as small as 0.3 /spl mu/m/spl times/0.2 /spl mu/m could successfully be detected. These marks were readout by the SIL head with a typical signal to noise ratio value of 36 dB. The present study demonstrates the capability to achieve a very high areal density beyond 20 Gb/in/sup 2/.