Papers by Keyword: Magnetic Recording

Abstract: This study investigates the performance of bit patterned media (BPM) in hard disk drives. It is revealed that written-in errors, rather than traditional signal-to-noise ratio, drive the recording performance of BPM. The staggered BPM structure allows for a larger write pole size, resulting in a larger write field. However, the lateral spacing between adjacent islands in staggered BPM is typically less than conventional BPM, leading to a higher written-in error rate. The investigation determines the effective switching field affected by the magneto-interaction field and finds that the write field is 21% higher in staggered BPM compared to conventional BPM. By analysing the error rate up to areal density of 5 Tb/in², the study shows that conventional BPM achieves 1 Tb/in² with the acceptable error rate, while staggered BPM can reach an areal density of 5 Tb/in² with tight synchronous writing requirements. These insights are useful for designing the structure of BPM in hard disk drives.

Abstract: Low temperature oxidized core-shelled magnetite is paramount important in recording geomagnetic field. To characterize the effects of transition zone between the core-shell on the magnetic properties of low temperature oxidation of magnetite, micromagnetic models of hysteresis parameters and microstructures of a multi-layer core-shelled model were systematically investigated by MERRILL (Micromagnetic Earth Related Rapid Interpreted Language Laboratory). Numerical simulations indicate that SD particles (<70 nm) remain highly uniform magnetization, but show decreasing coercivities as oxidation preceeds. For fine SV particles (80 nm to 120 nm), the hysteresis parameters respectively increase and dramatic decrease at the early and late stage of oxidation, and the micromagnetic behaviors vary significantly. Finally the hysteresis parameters of larger SV (>130) particles remain nearly unchanged during oxidation. It indicates that fine SV particles are more sensitive to oxidation, and dominate the dramatic change of experiment observation. Overall, low temperature oxidation of magnetite preferring a multi-layer coupled oxidation process from outside to interior and is capable of recording paleomagnetic signals.

Abstract: In this work, magnetic force microscopy (MFM) tips coated with a nickel thin-film were prepared and characterized for applications in the measurement of the magnetic write field. Nickel films with various thicknesses in a range of 20 – 80 nm were deposited on silicon substrates and silicon atomic force microscopy (AFM) tips by electron beam evaporation. Film surface morphologies and magnetic properties of the coated nickel films were investigated by using AFM and vibrating sample magnetometry (VSM). The rms roughness increased with the film thickness and was in a range between 0.1 and 0.3 nm. VSM results revealed that the mean coercive field of the nickel films was 20 Oe and there was an increase in the coercivity as the film thickness increased. In addition, the prepared MFM tips were evaluated for the tip response to the dc and ac magnetic field generated from perpendicular write heads. It was found that the MFM tip had the best response to the write field when coated with 60 nm thick nickel film. The coating thickness over 60 nm was inapplicable due to the cantilever bending caused by the film stress.

Abstract: CoPt-C films were fabricated on silicon substrate by dc reactive magnetron sputtering followed by vacuum annealing. The effects of C additions and annealing temperature on the microstructure and magnetic properties were investigated. The as-deposited films had flat, compact surfaces and face-centered cubic structure, which transforms into the face-centered tetragonal structure after thermal annealing at 700°C for 1 hour. The grain size of CoPt increased with the annealing temperature but decreased with increasing C content. No carbide appearing, the C content exists in amorphous state in the nanocomposite films, and it is homogeneous distributed between the CoPt nanograins, which have the benefit to restrain grain growth and obtain isolated CoPt particles with uniform size. The fct-CoPt films annealed at 700°C exhibited high in-plane coercivity, up to 4200 Oe at room temperature and better square degrees. In the CoPt-C granular films, the best doping amount is about 35 at.% C. These CoPt-C films with novel embedded structure and moderate coercivity have shown promise for high density magnetic recording medium.

Abstract: Constant increase of magnetic recording density requires application of modern ferromagnetic materials with high value of magnetic anisotropy constant and coercivity. Thin films on the bases of L1₀-FePt ordered phase is one of such materials. However, practical application of such materials requires to solve a number of materials science problems such as decrease of ordered phase formation temperature, formation of its predominantly oriented grains and increase of coercivity. Factors that affect structure formation and properties of FePt based films have been examined in this study. A number of modern studies aimed on solving problems mentioned above have been analyzed.

Abstract: A possibility to fabricate nanodot arrays with a dot size of <10 nm="" and="" a="" dot="" pitch="" of="" 12="" along="" guide="" lines="" has="" been="" studied="" for="" ultrahigh-density="" patterned="" media="" in="" magnetic="" recording="" this="" was="" by="" using="" self-assembling="" block="" copolymers="" polystyrene-poly="" dimethyl="" siloxane="" ps-pdms="" electron="" beam="" eb="" drawing="" with="" hydrogen="" silsesquioxane="" hsq="" negative="" resist="" their="" fusion="" method="" it="" demonstrated="" that="" the="" could="" possibly="" achieve="" 6-nm-sized="" nanodot="" arrays="" 10="" 4="" x="" sup="">2 using self-assembling with PS-PDMS of molecular weight 7000-1500 and EB-drawing for narrow guide lines. These results prove that the fusion method is required for achieving extremely small dot arrays as 5 Tbit/in² magnetic storage devices.Keywords: Nanodot, self-assembly, electron-beam drawing, graphoepitaxy, patterned media, magnetic recording.

Abstract: The magnetic anisotropy of Co/Ti-doped Ba ferrite particles for application in recording media is studied. A method which deduces the anisotropy from the measurement of the reduced perpendicular magnetization and allows to find also the distribution of anisotropy fields is employed. The effect of the doping ions content, of the alignment degree of the particles and of the variation of the temperature on the anisotropy is analysed and discussed, taking account of the contemporary presence of magnetocrystalline and shape anisotropy, with different easy magnetization axes, in the Ba ferrite particles.

Abstract: The elemental magnetic moments of Co and Cr in CoCrPt films were investigated using xray magnetic circular dichroism (XMCD). The spin and orbital moments of Co was calculated using the sum rules; it was found that the magnetic moment of Co in CoCrPt films was dominated by spin moment contribution. The total magnetic moment of Co was found to be lower than that of bulk Co. Further, the Cr moment was aligned anti-ferromagnetically with respect to Co, resulting in a decrease of saturation magnetization (Ms) in CoCrPt films.