We have studied propagation of magnetostatic surface waves in yttrium iron garnet films with attached 1D periodic arrays of metal strips. For different experimental geometries and different designs of 1D periodic arrays of metal strips, propagation spectra of magnetostatic surface waves were measured and analyzed. We have shown a way to control propagation characteristics of magnetostatic surface waves by changing of electrical contact between periodic metal strips.

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Thermally assisted magnetic recording (TAMR) is a promising technology to achieve a recording density of over several Tbit/inch². We analyzed the use of a plasmon antenna as well as the effect of a particle medium with Finite-Difference Time-Domain (FDTD) method. Using a plasmon antenna, we analyzed the dependence of flying height (FH) on the power intensity (E²). FH is the distance between the medium and the antenna. We also analyzed the dependence of full width half maximum (FWHM) on near-field optics. We investigated the influence of different compositions of the antenna and of the media on plasmon resonance. Three compositions of the particle medium were Au, Pt, and Co. For metallic particles, the FWHM was less than 15 nm when FH was 5 nm to 20 nm. The peak intensity for the particle medium was higher than that of the continuous film across various values for FH. Furthermore, the overall power distribution was higher as well. These results show that particles positioned at the apex of the antenna can be heated by a small, concentrated spot.

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Magneto-Optical (MO) recording on ultra thin discs with 92 μm thickness succeeded. Key technologies are a nano-imprint for embossing on the thin disc and aerodynamic stabilizer (ADS) for stable disc rotation. The ADS made the thin disc rotation stable by providing an air cushion between the glass stabilizer and thin disc. The ADS was also available for the thin disc with a magnetic flying head. Using TbFeCo film, the thin disc had almost the same performance as that of a normal disc with 1.2 mm thickness. Stacked Volumetric Optical Discs (SVOD) can enhance the volumetric capacity with a lot of thin discs stored in a compact cartridge. Because the 40 nm mark length recording corresponds to the 100 GB/disc with CD size which has already succeeded in MO recording, the combination of MO recording and SVOD with 100 thin discs will enable the possibility to provide a 10 TB cartridge capacity.

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We demonstrate a newly developed magneto-photonic crystal (MPC) based magneto-optic spatial light modulator (MOSLM) which was designed to enhance the performance of a conventional MOSLM, and describe the preparation and fundamental properties of it. By introduction of MPC, the magneto-optical property of MOSLM was improved, and as driving properties, the saturation of brightness was shown around ±1 kOe and the change occurred from about ±300 Oe by external magnetic field. Also, we conformed that Kerr rotation angle of this device was varied by applying voltage to PZT film. The change of each pixel by applying voltage, however, could not be detected because of the small variation of brightness.

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We present experiments on optical writing and erasing of microscopic magnetic domain patterns on an epitaxial ferrite-garnet film. The film is initially uniformly magnetized normally to the surface. A weak constant magnetic field pointing in the same direction as the magnetization is applied, and magnetic domain patterns are written and erased by locally heating the film with a pulsed focused laser beam. For switching the magnetization, in both directions, only the beam diameter and the peak power of the laser pulse need to be controlled; the direction and strength of the external magnetic field are kept unchanged. The switching is essentially all-optical, which widens the area of potential applications of the method. We also show that domain patterns can be optically recorded in multilayered ferrite-garnet samples. Large Faraday-rotation angles in our films enable both spatial and temporal observations of the magnetization reversal.

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The magneto-optic spatial light modulator (MOSLM) can modulate amplitude, phase, and polarization of optical wave front at high speed. However, past MOSLM requires large driving current. To overcome the disadvantage, we have developed the MOSLM with PZT layer driven by electric field and external magnetic field. The effective structure of the voltage-driven MOSLM was also investigated using finite element simulation. A magneto photonic crystal(MPC), which consists of dielectric mirror and magnetic defect layer, can largely enhance MO effect. The stress distribution calculation of MPC structure with good stress distribution and a large Faraday rotation was done based on a structure of a thin MO film.

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This paper described a specially synthesized novel polymer lubricant with high thermal stability for heat assisted magnetic recording media. The contact angle and touchdown/takeoff behaviors of the lubricant were investigated by comparing to commercial available lubricants. A thermal stability of the polymer lubricant at 449°C has been achieved. The results suggest that the takeoff/touchdown behavior of a slider over a lubricated hard disk depends on the molecular interactions of the lubricant molecules. Thermal stabilities of all the tested lubricants were found increasing with the heating rate and follow the same trend. A higher thermal stability of the lubricant film under flash heating and cooling conditions is predicted. A heat-sink layer was experimentally confirmed as effective approach to reduce the peak temperature duration onto the lubricant or carbon overcoat.

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Iron Garnet single crystals like Bi₃Fe₅O₁₂ are important ceramic systems with extensive applications in structural ceramics and optoelectronics. Currently, it is desirable to integrate such macroscopic components on a single chip (e.g. Si, SiO₂, ...) as in the case of microelectronics (integrated optics). High quality magneto-optical active garnet films with high Faraday rotation are also needed for magneto-optical imaging.
In our present work we studied the integration of Bi₃Fe₅O₁₂ on different SiO₂ substrates using the pulsed laser deposition method. Therefore we deposited a Y₃Fe₅O₁₂ buffer first which was optimized in a post-annealing step above 900 °C in order to form a polycrystalline garnet phase, which is needed for further Bi₃Fe₅O₁₂ growth.
We measured the Faraday rotation of the films and intensely studied them with x-ray diffraction, Rutherford Backscattering Spectroscopy, Environmental Scanning Electron Microscopy, X-ray photoelectron spectroscopy and High-Resolution Transmission Electron Microscopy. The attained Faraday rotation can be compared with epitaxial Bi₃Fe₅O₁₂ films grown on Gd₃Ga₅O₁₂ substrates.
Finally we present an easy solution to generate linear polarized light on the substrate by an organic light emitting diode, which can be coupled into to the garnet thin film.

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We reported simulated results of coupled granular and continuous (CGC)-like film, consisting of FePt granular under layer that act as a domain pinning of TbFeCo layer. For further increasing the recording density, grain diameter and period of each grain p have to be decreased until comparable scale with the domain wall width W_d and it causes difficulty to predict the domain structure. Simulated result shows it could be formed on p ≅ W_d (domain diameter D_d = 25 nm), which domain size is suitable to 1 Tbit/inch². Moreover, we clarified that D_d = 22 nm (it is suitable at 1.33 Tbit/inch²) at the TbFeCo surface and domain shape could be formed even under the condition of p < W_d. And we estimated the effective wall coercivity H_w from the simulation varying the applied magnetic field until domain is shrank and disappear. Suitable value of H_w ( >10kOe) was observed. Furthermore, to elucidate the details of this contribution by interfacial exchange coupling we carried out simulations while varying the values of interfacial exchange constant A_int over wide range. The observed pinning effect can be attributed to interfacial exchange coupling even much smaller value of A_int ( < 0.047 × 10^-6 erg/cm) comparing with A of TbFeCo (0.2 × 10^-6 erg/cm) and FePt (1.13 × 10^-6 erg/cm).

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We survey the properties of all-garnet magneto-optical (MO) heteroepitaxial film structures grown by pulsed laser deposition and rf-magnetron sputtering. 1D MO-photonic crystals (MOPCs) were composed of λ/4 garnet layers alternating highly gyrotropic Bi₃Fe₅O₁₂ (BIG) and MO-passive rare earth gallium garnets. As designed, MOPCs' spectra exhibit optical stop band with the transmittance central peak caused by light localization in λ/2 thick BIG cavity. The first all-garnet BIG/YIG MOPC showed 140% enhancement of the Faraday rotation (FR) compared to a single layer BIG film [APL 84, 1438 (2004)]. Further improvement of MO-performance has been achieved due to the replacement of optically dense YIG by transparent Gd- (GGG), Sm- and novel La-Ga-garnets [APL 86, 141108 (2005); 87, 122504 (2005); 90, 191113 (2007); JAP 101, 053906 (2007)]. At the resonance wavelengths 750 (980) nm, specific FR θ_F = −20.5 (−7.3) deg/μm and MO-quality factor Q=2 | θ_F | /absorption=66 (43.6) deg represent the highest MOPC performance achieved so far. Respectively, this is 470 (810) % and 31 (190) % enhancement compared to a single layer BIG. MO-remanence (latching capability) has been engineered in the series of BIG:GGG (n:m) superlattices. Regular alternating of lattice mismatched garnet layers impedes the nucleation of misfit dislocations, preserves a long range coherent compressive strain through the whole multilayer thickness thus results in a strong uniaxial magnetic anisotropy. 2.5 μm thick BIG:GGG (3:2) film at 678nm shows FR = ± 1.4deg, transmittance 82%, 92% squareness of magnetization loop, saturation and coercive fields as low as 56 and 25 Oe, respectively. Nanostructured garnets were used to build MO-visualizer and current driven MO-display [APL 88, 242504 (2006)].

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To meet the ever-growing demand for digital storage, the recording industry has been maintaining a phenomenal growth in the data storage density. This growth has been maintained by increasing the anisotropy of each of the grains each time their volume was decreased. Heat Assisted Magnetic Recording will allow this scaling to continue by removing the write-ability barrier; Heating the medium during the write process lowers the anisotropy, such that even with a modest magnetic field a bit can be switched, yet remain thermally stable at ambient temperature. In this paper we will address three major challenges that were overcome to successfully put together a Heat Assisted Magnetic Recording system.

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Bi-substituted yttrium iron garnet, Y_3-xBi_xFe₅O₁₂ (Bi:YIG, x = 1, 1.5), films were prepared on Gd₃Ga₅O₁₂ (111) substrates by metal-organic decomposition (MOD) method to use as MO indicator films. Those films had the in-plane magnetic anisotropy and Faraday rotation as large as that of the single crystal and do not show prominent magnetic domain structure, which is often observed in single crystalline garnet films grown by liquid phase epitaxy method. Disappearance o magnetic domain structure can be attributed to a granular structure with a grain size of ∼ 50 nm in Bi:YIG thin films. The characteristics are suitable for MO indicator films to visualize a stray magnetic field strayed from a specimen. In this paper, MO imaging of Nb films with groove patterns is demonstrated.

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Simulation of near-field assisted recording using the finite-difference time-domain (FDTD) method and thermal analysis was carried out. Improvement of optical coupling efficiency between nano-patterned medium and optical near-field probe is the most important issue to design and optimize heat assisted near-field magnetic recording system. We propose the new nano-patterned medium structure that constructs the multi layer structure of silver and magnetic recording material. Local plasmon enhancement of silver layer is effective in order to improve optical near-field coupling efficiency of nano-patterned medium. The generated heat at silver layer conducts into magnetic recording material layer.

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Heat assisted magnetic recording head needs near-field element as a micro heat generator and light guide structure. We have proposed a triangular aperture as a near-filed element. Computer simulation using finite difference time domain (FDTD) method shows that the triangular aperture has a near-field peak on the edge perpendicular to the polarization of the incident light. Therefore it achieves a near-field spot less than 20 nm (FWHM) in the direction of the polarization, which is not limited by the aperture size. SNOM and contact slider experiments in the previous study also show that the triangular aperture is effective. We have also proposed a compact light guide structure with an optical fiber. Using light guide structure with a polarization maintaining fiber and micro optics can achieve a thin and small (1.6x1.6x0.7 mm) near-field flying head. The head was fabricated. Signal readout was demonstrated in flying operation. It could read 300 nm L&S patterns.

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Heat assisted magnetic recording(HAMR) is a magnetic recording method that circumvents the superparamagnetic limit by heating the media. We investigate the effects heat leakage will have on the decay of tracks adjacent to the hot spot by measuring the distribution of energy barriers to thermal flipping. The energy barrier distribution width is found to increase with temperature in a medium sample. This effect will result in more decay at adjacent track aging temperatures than would be predicted by the scaling of measurements made at room temperature.

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We developed a multilayer optical head with a planar structure that was designed using the finite-difference time domain (FDTD) method for hybrid recording. This optical head has a butted-grating structure, including its central and side parts. We initially discuss the advantages of the method of end-fire coupling for using the planar optical head. Second, we briefly explain our optical head and demonstrate how it can project a single-peak spot, even if multimode light is supplied by end-fire coupling that can be used. Finally, we present details on the asymmetric butted-grating optical head to position the output beam close to the magnetic writer pole in practical use.

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We have proposed a novel thermally assisted magnetic recording head for future hard disk drives using a “Focusing Waveguide” (waveguide-type spot size converter). The Focusing Waveguide, which has a small size enough to be integrated into a flying slider, can focus the spot diameter of incident light less than one tenth while the light propagate only 200 μm in the waveguide. The focused spot illuminates a plasmon antenna to generate an enhanced near-field spot for heating a very small region of a recording media. We fabricated the Focusing Waveguide and evaluated its focusing properties by means of SNOM measurement method. A measured spot size was 0.37 μm × 0.42 μm (FWHM, Incident spot size = 5 μm). Since a core of the Focusing Waveguide is made of silicon, wavelength of the incident light was set to be 1310 nm. In order to examine the plasmon enhancement of the gold plasmon antenna at this wavelength, FDTD simulations and SNOM measurement was conducted. The results have shown that the combination of a gold plasmon antenna and the silicon substrate gives the fairly good plasmon enhancement at the wavelength of 1310 nm.

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