S. N. Piramanayagam

Perpendicular recording media for hard disk drives

Perpendicular recording technology has recently been introduced in hard disk drives for computer and consumer electronics applications. Although conceptualized in the late 1970s, making a product with perpendicular recording that has competing performance, reliability, and price advantage over the prevalent longitudinal recording technology has taken about three decades. One reason for the late entry of perpendicular recording is that the longitudinal recording technology was quite successful in overcoming many of its problems and in staying competitive. Other reasons are the risks, problems, and investment needed in making a successful transition to perpendicular recording technology. Iwasaki and co-workers came up with many inventions in the late 1970s, such as single-pole head, CoCr alloy media with a perpendicular anisotropy, and recording media with soft magnetic underlayers [S. Iwasaki and K. Takemura, IEEE Trans. Magn. 11, 1173 (1975); S. Iwasaki and Y. Nakamura, IEEE Trans. Magn. 14, 436 (1978); S...

Influence of dual-Ru intermediate layers on magnetic properties and recording performance of CoCrPt–SiO2 perpendicular recording media

CoCrPt–SiO2 perpendicular recording media containing dual-Ru intermediate layers have been studied. The bottom Ru layer deposited under a higher mobility condition, i.e., low Ar gas pressure and bias on substrate, helps to achieve a good crystalline texture, and the top Ru layer under a lower mobility condition, i.e., high Ar gas pressure, promotes the formation of a columnar microstructure. Three kinds of grain boundaries have been observed. The nucleation field and the coercivity as a function of the thickness and dc bias of the bottom Ru layer have been investigated. Medium noise reduction has been observed for dual-Ru intermediate layer media (dual-Ru media) in comparison with that of single intermediate layer media (single-Ru media). This is mainly attributed to the optimization of the physical grain segregation.

Micromagnetic study of spin wave propagation in bicomponent magnonic crystal waveguides

The propagation of spin waves in bicomponent magnonic crystal waveguides has been investigated by micromagnetic simulations. The nanostructured waveguides studied are regular square lattice arrays of circular Fe dots embedded in an yttrium iron garnet matrix. Our simulations show that the waveguides exhibit wide magnonic band gaps of the order of 10 GHz. Band gap tunability, arising from variations in the filling fraction, lattice constant, and applied magnetic field has been demonstrated. Our findings would be of value to the efficient transmission and processing of microwave signals on the nanoscale by means of spin waves.

Patterned Media Towards Nano-bit Magnetic Recording: Fabrication and Challenges

During the past decade, magnetic recording density of HDD has doubled almost every 18 months. To keep increasing the recording density, there is a need to make the small bits thermally stable. The most recent method using perpendicular recording media (PMR) will lose its fuel in a few years time and alternatives are sought. Patterned media, where the bits are magnetically separated from each other, offer the possibility to solve many issues encountered by PMR technology. However, implementation of patterned media would involve developing processing methods which offer high resolution (small bits), regular patterns, and high density. All these need to be achieved without sacrificing a high throughput and low cost. In this article, we review some of the ideas that have been proposed in this subject. However, the focus of the paper is on nano-imprint lithography (NIL) as it fulfills most of the needs of HDD as compared to conventional lithography using electron beam, EUV or X-Rays. The latest development of NIL and related technologies and their future prospects for patterned media are also discussed.

Grain size reduction in CoCrPt:SiO2 perpendicular recording media with oxide-based intermediate layers

CoCrPt–SiO2 perpendicular recording media containing an oxide-based intermediate layer have been studied in order to minimize the grain size in the recording layer. A RuCr alloy thin film deposited in an argon and oxygen reactive atmosphere was found to produce finer grains in the intermediate layer. When the recording layer was deposited on such an intermediate layer, the grain size of the recording layer was also observed to be smaller (about 6.4nm center-to-center distances). The results indicate that the introduction of RuCr-oxide-based intermediate layers is a possible approach to reduce the grain size in perpendicular recording media.

Developments in data storage : materials perspective

Preface. Acknowledgments. 1. Introduction. 2.Fundamentals of Magnetism. 3. Longitudinal Recording Media. 4. Perpendicular Recording Medium. 5. Writer heads Fundamentals. 6. Magneto-resistive Read Heads: Fundamentals and Functionality. 7. Read sensors for over 1 Terabits per square inch. 8. Thin film media Lubricants: Structure, Characterization and Performance. 9. Overcoat Materials for Magnetic Recording Media. 10. Heat Assisted Magnetic Recording. 11. L lo FePt for Magnetic Recording Media Applications. 12. Patterned Magnetic Recording Media: Progress and Prospects. 13. Phase Change Random Access Memory. 14. Non-volatile Solid State Magnetic Memory.

Magnetic and transport properties of Co-doped Fe3O4 films

We present a systematic study of the structural, magnetic, and magnetotransport properties of Co-doped Fe3O4 films deposited on MgO (100) substrates by cosputtering technique. Transmission electron microscopy images suggest that the undoped and Co-doped Fe3O4 films are polycrystalline in nature and consist of a well defined grain boundary network. The temperature dependence of resistance also shows that the transport mechanism in our films is dominated by electron tunneling across antiferromagnetically coupled grain boundaries. We observed that the magnetic properties of the doped films are markedly sensitive to the Co doping concentration, with the magnetization curves showing drastic changes in coercivity with increasing doping concentration. In-plane magnetoresistance curves show linear magnetic field dependence for the undoped Fe3O4 films while a reduction in magnetoresistance and a departure from linear field dependence are observed for the Co-doped films.

Spin transfer torque switching for multi-bit per cell magnetic memory with perpendicular anisotropy

A novel multi-bit dual pseudo spin valve with perpendicular magnetic anisotropy is investigated for spin transfer torque (STT) switching. The structure consists of two free layers and one reference layer, and all are based on Co/Pd multilayer. STT switching of the multi-bit device shows distinct four resistance levels. The selection of intrinsic properties of each ferromagnetic layer can be controlled for distinct separation of the resistance levels as well as the respective STT switching current. Reversible transitions between different states can be achieved by a pulsed current, in which its critical value is found to be linearly dependent on pulse duration.

Effect of magnetostatic energy on domain structure and magnetization reversal in (Co/Pd) multilayers

Magnetization reversal in (Co/Pd) multilayers with perpendicular anisotropy for different numbers of bilayers (N) is investigated experimentally and by theoretical modeling. The focus of this study is on the magnetostatic energy in these structures and its effect on the magnetization reversal behavior and the nature of domain formation. For (Co/Pd) multilayers with small N, sharp magnetization switching and large domains were observed. In contrast, (Co/Pd) multilayers with a large N have long tail in the hysteresis loop that gets more pronounced as N increases. The size of domains becomes considerably smaller as N increases. Based on theoretical modeling that takes into account of the magnetostatic energy from the different magnetic layers, the domain size dependence on the number of bilayers is explained. For large N, the tail in the hysteresis loop is revealed to be the result of an increase in the magnetostatic energy, which at the same time leads to a drastic reduction in domain width.

Advanced perpendicular recording media structure with a magnetic intermediate layer

CoCrPt–SiO2 perpendicular recording media containing a CoCr-based magnetic layer as an intermediate layer was studied. CoCr film deposited on a growth control layer such as Ta could grow with a hcp[0002] out-of-plane orientation, which could induce the desired perpendicular easy-axis orientation for the CoCrPt:SiO2 magnetic layer. It was observed that the growth of an intermediate layer based on Ru between the magnetic intermediate layer and the magnetic recording layer is crucial to reduce the noise. Recording performance of disks with a magnetic intermediate layer was comparable or better than that of conventional perpendicular media indicating the potential of the proposed structure.