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For bit patterned media (BPM) applications, while significant progress has recently been made in demonstrating high-resolution dot patterning using e-beam direct writing, and followed by the successful imprint process, many serious issues in fabrication still remain. This paper will only discuss the key challenges in the BPM lithography, including 1) the commercial availability of a high-resolution rotating stage e-beam system; 2) the approach and limitation of directed polymer self-assembly for resist pattern quality improvement and resolution enhancement; 3) the difficulties and limitations in the fabrication and replication of a 1 x template with a density beyond 1 Tbit per square inch (Tb/[in.sup.2]), while the defectivity, lifetime, and damage of the template are still questionable; 4) the tight requirements of size uniformity and placement accuracy; and 5) the needs of advanced metrology associated with the very small dot size and defect characterization. In this paper, we will address the above challenges and present some experimental data along with possible solutions for the challenges. Index Terms--Advanced lithography, bit patterned media, directed self-assembly, nanoimprint lithography.

A complex transverse ac susceptibility ([[chi].sub.T]) technique based on magneto-optical detection has been developed with sufficient sensitivity for thin-film recording media. The technique has been used to measure the dispersions in grain size and the anisotropy field of perpendicular magnetic recording media. Experiments have been designed to study the key factors contributing to the anisotropy field distribution ([sigma][H.sub.k]) in perpendicular media. The correlation between anisotropy dispersion, stacking faults, and recording performance have also been studied. A good correlation between stacking faults and [sigma][H.sub.K] has been established. Lower stacking faults result in smaller anisotropy distribution and better media signal-to-noise ratio. The main factors controlling stacking faults are studied. Theoretical studies of the effect of interactions on the [[chi].sub.T] are also presented. Index Terms--AC suseptibility, anisotropy distribution, magnetic recording, perpendicular media, stacking faults.

Due to the limits of conventional perpendicular magnetic recording, it appears that alternative technologies are needed at areal densities >500 Gb/[in.sup.2]. Heat-assisted magnetic recording (HAMR) is a promising approach to extend areal densities to 1 Tb/[in.sup.2] and beyond. All of the unique components necessary for a working HAMR system have been demonstrated. Although HAMR permits writing on high Hc media with lower magnetic fields and can produce higher write gradients than conventional magnetic recording, head/media spacing and the development of high Hc media with small grains remains challenging. Index Terms--Heat-assisted magnetic recording (HAMR), high-density recording.

A complex transverse alternating-current (ac) suspectibility [X.sub.T] technique based on magneto-optical detection is developed with sufficient sensitivity for thin film recording media. The technique is used to measure the dispersions in grain size and anisotropy field in perpendicular magnetic recording media.

The selected aspects of the recording physics of magnetic data storage specific to writing and reading in patterned medium are discussed. The influence of a recording layer design on playback resolution is evaluated, which offers guidelines for the design and optimization of patterned magnetic recording medium.

Exploring new Co-alloy composition to achieve both chemical segregation and suitable magnetic properties is a priority task for the development of the future perpendicular magnetic recording media. With proper interlayer (IL) design, columnar Co-alloy grains with narrow orientation distribution ([DELTA][[theta].sub.50] < 6[degrees]) have been obtained on thin IL (4 nm thick). We demonstrate CoCrPtB-alloys with full remanence squareness and large negative reverse field ([H.sub.r] < -1.5 kOe) at low IL and magnetic layer thickness of 4 and 11 nm, respectively. It is also shown that carbon overcoat thickness reduction results in a signal-to-noise ratio gain of about 0.5 dB/nm. Index Terms--Co-alloy, microstructure, perpendicular magnetic recording media, recording performance.

Numerical and analytical calculations of rotational process in perpendicular recording media are presented. The work supports recent experimental studies that suggest that the measurement of rotational magnetization processes can be used to determine the value of the anisotropy constant. An expression for the rotational magnetization for a noninteracting system is derived taking into account the dispersion of K and the easy-axis orientation. The calculations show that the experiments determine the mean value of [H.sub.K], essentially independent of the angular dispersion. A numerical (Monte-Carlo based) micromagnetic model is used to study the effects of magnetostatic and exchange interactions at nonzero temperatures. It is shown that for small values of KV/kT, irreversible magnetization processes take place, which precludes the use of the rotational magnetization method to determine K values. This effect is enhanced by the presence of the magnetostatic interaction. However, the presence of exchange interactions is found to enforce coherent rotation in small fields, reducing the irreversible processes and allowing the determination of [H.sub.K]. Under these circumstances, it is shown that the exchange does not significantly affect the value of [H.sub.K], and that a well-defined demagnetization correction of 4[pi] M is appropriate. Finally, a comparison with experimental data gives good agreement for multilayer and granular media and shows the role of domain formation on the rotational magnetization process. Index Terms--Anisotropy, micromagnetics, perpendicular media, rotational magnetization.

We present a novel experimental method to determine the switching field distribution in perpendicular thin-film magnetic recording media. The method assumes a constant demagnetization factor independent of the magnetic state during switching and a log-normal switching field distribution. The new technique allows a deconvolution of the effects of the switching field distribution and demagnetization, which is important for the development of low-noise perpendicular magnetic recording media. Index Terms--Magnetic characterization, magnetization reversal, perpendicular recording, switching field distribution.

The problem of energy shortage and environmental pollution is becoming remarkably important and has attracted much attention. Driven by this situation, self-powered devices are highly desirable in all areas. Herein, a broadband photoresponse, self-powered, polarization-sensitive photodetector based on stacked two-dimensional type-II GaSe/ReS2 heterostructures is demonstrated. Because of the formation of the type-II band alignment, GaSe/ReS2 heterostructures display a self-powered photoresponse with an Ion/Ioff ratio of about 8.3 × 102 and exhibit a high responsivity of 54 mA/W under illumination with 532 nm laser light. A maximum photoresponsivity of 170 mA/W and an external quantum efficiency of 10% can be achieved by illumination with a 340 nm laser. Additionally, benefiting from the highly in-plane anisotropic atomic arrangements of ReS2, the photodetector shows a polarization-sensitive photocurrent. The dichroic ratio and polarization sensitivity are determined to be 1.73 and 3.03, respectively, and the highest photoresponsivity of the photodetector can reach up to 94 mA/W when the direction of the incident polarized laser is parallel to the b-axis of ReS2. Importantly, the self-passivating behavior of GaSe can maintain the performance of the heterojunction for 1 week. The present findings open new opportunities for developing air-stable, high-performance van der Waals heterostructure photodetectors. [ABSTRACT FROM AUTHOR]

Design considerations for areal densities beyond 20 Gb/in.(super 2) are discussed. The demonstration profited by more advanced channels, modeling and experiment showed that it was not required to reduce the bit-aspect ratio.

The transformation temperature in low-temperature phase and high-temperature phase is lowered by the partial substitution of chromium (Cr) for manganese in manganese bismuth (MnBi) film from 360 to 250 degrees Celsius without affecting the magneto-optical properties, in which case the magnetic and structural transformation decoupling is completed. This is considered one of the merits of alloying MnBi thin films with Cr.

The coercivity mechanism of (Co/Pt) multilayers with high Hc and high squareness fabricated by sputtering is mainly due to the wall-pinning rather than the nucleation process. In order to estimate the size of a wall-pinning site, a study of the temperature dependence of the coercivity, perpendicular magnetic anisotropy, and saturation magnetization for multilayers fabricated under various substrate conditions has been carried out. The size r(sub o) of the pinning sites of about 4A was obtained for the multilayer film deposited onto an etched SiNx film. The size r(sub o) increases with less interface-sharpness, confirmed by X-ray low angle diffraction. This implies that the pinning site is closely related to the interfacial region. The result is compared to the case of Tb26(FeCo)74 films in which case the size is found to be about 60A is similar to 250A.

Selected aspects of the recording physics of data storage systems based on patterned magnetic recording medium are discussed. The micromagnetic study of the magnetization reversal in patterned magnetic recording medium is presented. The effects of bit size, head/medium misregistration, bit-to-bit spacing, soft underlayer (SUL) patterning, and side wall roughness on magnetization reversal are explored. The results offer the guidelines for the design and optimization of patterned magnetic recording medium. Index Terms--Bit magnetization reversal, micromagnetics, patterned medium recording.

We report on the fabrication of 1 Tdot/in² bit patterned media with high coercivity (HC) and narrow intrinsic switching field distribution (iSFD) based on nanoimprint from a master pattern formed by e-beam guided block copolymer assembly onto a carbon hard mask and subsequent pattern transfer via etching into a thin CoCrPt perpendicular anisotropy recording layer. We demonstrate that an additional vacuum annealing step after pattern transfer into the CoCrPt layer and after Carbon hard mask removal not only yields recovery from undesired damage of the island edges, but actually transforms the islands into a magnetically more favorable compositional phase with higher HC, lower iSFD/HC, and three-fold increased thermal stability. Energy filtered transmission electron microscopy analysis reveals that the diffusion of Cr from the island cores to the periphery of the islands during post-annealing is responsible for the transformation of the magnetic bits into a more stable state. [ABSTRACT FROM AUTHOR]

A new experimental method has recently been proposed to determine the switching field distribution for perpendicular media. The advantage of the new technique is that it separates the effects of the switching field distribution and the effective demagnetization factor, which are difficult to estimate independently. In this paper, this methodology is extended to the [DELTA]M measurement, which is an indicator for intergranular exchange interactions. We present the magnetic properties for a set of CoCrPt alloy media and a set of [[CoX-Pd].sub.N] based multilayer perpendicular media. We correlate the effective demagnetization factor and the width of the switching field distribution to the exchange interaction and recording performance. Index Terms--Magnetic characterization, magnetization reversal, perpendicular recording, switching field distribution.

The noise performance of amorphous FeCoB soft underlayers (SULs) with radial magnetic anisotropy is examined. The internal stress declines with thermal annealing as the increase in annealing power reduces the dc noise and the SUL-induced dc noise drops to the electronic noise floor.