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In this paper, magnetic and structural properties of near-equiatomic CoPt thin films, which exhibited a high coercivity in the film-normal direction-suitable for perpendicular magnetic recording media applications-are reported. The films exhibited a larger coercivity of about 6.5 kOe at 8 nm. The coercivity showed a monotonous decrease as the film thickness was increased. The transmission electron microscopy images indicated that the as fabricated CoPt film generally consists of a stack of magnetically hard hexagonal-close-packed phase, followed by stacking faults and face-centred-cubic phase. The thickness dependent magnetic properties are explained on the basis of exchange-coupled composite media. Epitaxial growth on Ru layers is a possible factor leading to the unusual observation of magnetically hard hcp-phase at high concentrations of Pt. [ABSTRACT FROM AUTHOR] more...

Spin reorientation in antiferromagnetically coupled (AFC) Co/Pd multilayers, wherein the thickness of the constituent Co layers was varied, was studied. AFC-Co/Pd multilayers were observed to have perpendicular magnetic anisotropy even for a Co sublayer thickness of 1 nm, much larger than what is usually observed in systems without antiferromagnetic coupling. When similar multilayer structures were prepared without antiferromagnetic coupling, this effect was not observed. The results indicate that the additional anisotropy energy contribution arising from the antiferromagnetic coupling, which is estimated to be around 6×106 ergs/cm3, induces the spin-reorientation. [ABSTRACT FROM AUTHOR] more...

In this report, a method to determine the dynamic remnant coercivity over a larger time-scale is proposed. Dynamic coercivity is also measured by a few existing methods. The stability factor measured from all these methods is used to compare different techniques. It is suggested that measurement of dynamic remnant coercivity is more suitable than the measurement of dynamic coercivity. Index Terms--Dynamic coercivity, remnant coercivity, Sharrock's equation, thermal stability factor. more...

Effect of exchange-bias coupling between ferromagnetic (FM) layer and antiferromagnetic (AFM) underlayer on the H-field and thermal reversal properties was studied analytically by minimizing the free energy E([Alpha], [Beta]) of the bilayer system. Correlation between the effective-thermal-stability-factor [([K.sub.u] V*/[k.sub.B] T).sub.eff], coercivity [H.sub.C] and parameters of the bilayer system is presented. Emphasis is on analyzing the energy-barrier [E.sub.B] influence upon the moment reversal properties. Index Terms--Antiferromagnetism, exchange-bias, switching volume, thermal activation, thermal stability. more...

Analytical solutions for coercivity [H.sub.CM1], [H.sub.CM2], effective [(Mrt).sub.eff], energy-barrier and effective thermal stability factor as a function of coupling constant J and other film parameters have been derived for two coupled ferromagnetic layers (FM-FM layer) with different magnetic properties for the first time. The condition for reduced effective [(Mrt).sub.eff] is analyzed. These results are valuable for laminated antiferromagnetically coupled media design. This may open up a channel to raise thermal stability significantly while maintaining lower noise for longitudinal recording media. Index Terms--Antiferromagnetically coupled film, energy barrier, magnetic recording media, thermal stability. more...

Recently proposed antiferromagnetic-coupled (AFC) media is studied in detail. The parameters, which control the switching field of the stabilizing layer and hence, the [M.sub.r][Delta] reduction are understood by theory and experiment. It was observed that the switching field of the stabilizing layer could be controlled by experimental parameters to be on either side of remanence. [M.sub.r][Delta] reduction could be achieved by a reduction of anisotropy constant, thickness or magnetization of the stabilizing layer. The coercivity and thermal stability of the AFC media is larger than that of a single magnetic layer. Index Terms--Anisotropy, antiferromagnetic coupling, magnetic recording, recording media, thermal stability. more...

Magnetostatic interactions in patterned media are responsible for increasing the switching field distribution and reducing the thermal stability. Micromagnetic simulations indicate that a reduced saturation magnetization (Ms) and increased anisotropy constant (Ku) lead to better thermal stability. However, writability will be a concern with this approach. Patterned media with an antiferromagnetically coupled (AFC) recording media structure is studied to obtain high thermal stability even with a larger Ms and larger Ku. With the AFC structure, the reduced remanence magnetization (Mr) leads to a reduced magnetostatic interaction, even though the Ms is larger. Magnetic force microscopy measurements indicate that the AFC media show a narrower switching field distribution. [ABSTRACT FROM AUTHOR] more...

CoRuCr-oxide based intermediate layers have been introduced as a replacement for pure Ru-based intermediate layers in perpendicular recording media. It was observed that the CoRuCr intermediate layers provide better C-axis orientation than the Ru intermediate layers. The introduction of oxygen during the deposition of CoRuCr increases the C-axis dispersion slightly but it is still comparable to that of Ru intermediate layer. Grain size and grain size distribution were reduced with CoRuCr-oxide intermediate layers. Magnetic properties were also optimized, indicating that the CoRuCr-oxide intermediate layers are good candidates for perpendicular recording media. [ABSTRACT FROM AUTHOR] more...

Thermally stable, highly textured CoCrPt–SiO2 perpendicular magnetic recording media with ∼6 nm size exchange decoupled grains and tight grain size distribution were prepared on synthetic nucleation layers. The media structure consisted of 14 nm thick CoCrPt–SiO2 recording layer on one Ru intermediate layer. For these films, insertion of a synthetic nucleation layer directly under the recording layer was seen to reduce the grain sizes from 6.7 to 6.2 nm and grain size distribution from 17% to 14%. Significant reduction in the intergranular exchange coupling interactions could be achieved while improving magnetic properties. The crystallographic texture of the recording layer remained strongly (00·2) oriented with the dispersion Δθ50 below 3.7°. Isothermal remanence magnetization and thermal stability behavior were studied. A model that describes the role of the synthetic nucleation layer in affecting the grain growth and magnetic properties of the recording layer is presented to understand these observations. [ABSTRACT FROM AUTHOR] more...

A novel hybrid magnetic overcoat (Hy-MOC), consisting of a bilayer, suitable for ultrahigh density recording, has been proposed and investigated. The top layer is a thin layer of carbon (about 1 nm) employed mainly for the purpose of lubrication affinity. The bottom layer is a thin CoCrPt alloy layer with silicon oxide/nitride grain boundary (about 4 nm), which helps as an overcoat to prevent corrosion and also in reducing the magnetic spacing. Media prepared with such an overcoat showed a better recording performace and thermal stability than the media with a-C overcoat. The microstructure of the media with carbon overcoats and the magnetic overcoats obtained by transmission electron microscopy were comparable. Improved corrosion protection properties were also observed. These results indicate that Hy-MOC provides a possible solution for ultrathin overcoat system necessary for ultrahigh density media. [ABSTRACT FROM AUTHOR] more...

The transfer of spin angular momentum from a polarized current to a ferromagnet can induce reversal of magnetization and generation of spin waves. In this article, we present micromagnetic simulations of magnetization dynamics in spin valve structure under effect of spin-polarized current and external magnetic field. Unlike the previous studies, the magnetizations of pinned layer, and the free layer in this study are orthogonal. Such a configuration, which is closer to that of the spin-valve sensors, shows many interesting results such as the observation of steady and oscillatory states. [ABSTRACT FROM AUTHOR] more...

We present a simple fabrication of FePt and Fe nanocomposite by annealing self-assembled FePt nanoparticles. 5 nm FePt nanoparticles were prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in the presence of oleic acid and oleylamine as stabilizers. The as-synthesized FePt nanoparticles can self-organize well on a clean SiO/Si substrate and, then, were annealed in a vacuum using a rapid thermal process at different temperatures for 0.5 h. It is found that the annealing temperature plays a key role in determining the final products. The samples annealed at 550 °C and 700 °C consist of a FePt-face-centered-tetragonal (fct) phase with a coercivity of around 1000 and 8800 Oe, respectively, whereas, the samples annealed at 580 °C are composed of two phases: one is the FePt-fct phase and the other is a Fe-body-centered-cubic phase. The hysteresis loop of the sample annealed at 580 °C is also two-phase like with a kink at low field and its coercivity is around 8000 Oe. That indicates that Fe can be segregated from FePt by proper annealing, forming FePt and Fe nanocomposites. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR] more...

[variant_greek_epsilon]-cobalt nanoparticles with different shapes and sizes, e.g., rod-shaped Co (2×25 nm) and ball-shaped Co (diameter 4–9 nm), were synthesized by the rapid pyrolysis of octacarbonyldicobalt in o-dichlorobenzene solution in the presence of the surfactant, oleic acid. The size, size distribution, and the shape of the nanoparticles were influenced by changing the preparation conditions, such as the molar ratio of the surfactant (oleic acid) to reactant (cobalt carbonyl). The effects of the preparation conditions and annealing temperature on the shape and magnetic properties of cobalt nanoparticles have been investigated. It was found that as-synthesized rod-shaped cobalt nanoparticles (2×25 nm) show paramagnetic properties, but as-synthesized ball-shaped cobalt nanoparticles exhibit superparamagnetic behavior. After postannealing at 773 K for 30 min, the rod-shaped Co nanoparticles formed hcp structure and show ferromagnetic properties. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR] more...

In this study, we propose a new "atomic wall" approach to underlayer design. In this design, a CrX underlayer is used where X and Cr are not miscible in the bulk phase, resulting in a reduced grain size. We have studied the addition of Zr to Cr layers and found that CrZr gives magnetic properties comparable to those of CrMo underlayers. In addition, a CrZr underlayer gives rise to a smaller grain size of 5.5 nm, in comparison to a grain size of 6.2 nm in the case of CrMo underlayers. To our knowledge, this is the smallest grain size reported for Co-alloy recording media. The recording measurements also show a higher signal to noise ratio for CrZr underlayers than for CrMo underlayers, suggesting that CrZr underlayers have potential for use in ultrahigh areal densities. [ABSTRACT FROM AUTHOR] more...

In this report, we will present our experimental and micromagnetic simulation studies to show that laminated antiferromagnetically coupled media has potentials to push the areal density beyond 100 Gbit/in². Exchange coupling constant as high as 0.32 erg/cm² has been obtained for basic two layer configuration by inserting an ultrathin Co interface layer between CoCrPtB and Ru layers, which is 3-4 times higher than the reported values in literature. This technique improved the thermal stability factor by more than 40%. A type of sandwich three-layer configuration for the antiferromagnetic coupled media is proposed which may double the antiferromagnetic coupling effect for the recording CoCrPtB layer. It also can further reduce the M[sub r]t value (less than 0.2 memu/cm²) while keeping high thermal stability that may be preferred for future application once extreme high sensitivity read head appears. [ABSTRACT FROM AUTHOR] more...

This paper describes numerical magnetohydrodynamic (MHD) calculation of heat plasma used in heating and welding processes. Most of the calculation models have been two dimensional and static. Since physical phenomena are three dimensional and nonstatic, three dimensional, dynamic MHD calculation of heat plasma is developed in this paper. Since local heat balance is assumed, the heat plasma is considered as a conductive fluid dynamic material such as molten metal. However, heat plasma's material constants such as density, heat transfer coefficient, specific heat, and electrical conductivity are strong functions of the temperature. Temperature is governed by heat plasma material transfer and heat transfer. Material transfer is driven by the electromagnetic force. Turbulent flow is modeled by the large eddy simulator including heat transfer. The electrical phenomenon is modeled using the Poisson equation in a dc magnetic field. It is assumed that the static electrical force may be ignored. Calculations show that the heat plasma concentrates at the center. The center area is of low density and high electrical conductivity. To verify the usefulness of this 3D dynamic MHD method, a conventional model, which is 2D and static is compared to a k - ε model. Comparison of velocity distributions shows good agreement. [ABSTRACT FROM AUTHOR] more...

Magnetic and structural properties of Co80Pt20 films were modified by controlled ion implantation through a dot-patterned mask for possible application in the mass production of patterned recording media. The dot patterns were fabricated using self-assembly of di-block copolymers. The effects of 14N + and 40Ar+ ion implantation at energies as high as 40 and 100 keV, respectively, were studied. Although both ions cause changes in the structural and magnetic properties, 40 Ar+ ion implantation leads to more significant changes. The structural changes, predicted using simulations and experimentally observed using X-ray diffraction, indicate a mixing of Co into the layers below, leading to layers richer in Pt at the top. Magnetic force microscopy measurements show an increase in domain width and domain wall thickness as a function of ion fluences. The results are analyzed with measurements of magnetic anisotropy constant and micromagnetic simulations. [ABSTRACT FROM PUBLISHER] more...

Examines the magnetic and conversion electron Mössbauer spectroscopy in iron/tantalum multilayers. Analysis of the spectra; Ways in which the fitting for all spectra were carried out; Factor which indicates the presence at each interface of a dead iron layer. more...

Studies the change in the temperature coefficient of resistivity with manganese (Mn) addition in iron- and cobalt-rich amorphous alloys. Difficulty of determining the temperature dependence of electrical resistivity in amorphous ferromagnetic materials; Effect of the substitution of iron in the presence of Mn on the temperature coefficients of resistivity; Functional form of positive temperature coefficients of resistivity. more...

Partial crystallization in amorphous magnetic film is observed in this study. The film of Co46Fe46Zr5B3/Ru/Co46Fe46Zr5B3 (CFZB/Ru/CFZB) was prepared on glass substrate by DC magnetron sputtering. The CFZB underlayer (CFZB-UL) and the CFZB overlayer (CFZB-OL) were deposited under nominally same sputtering conditions, i.e. target, working gas, working pressure, input power, and deposition duration. The transmission electron microscopy (TEM) images with fast Fourier transform (FFT) patterns revealed that the CFZB-UL was amorphous while the CFZB-OL became unexpectedly partially crystallized. The result of X-ray diffraction (XRD) spectra verified the TEM observation. The cause of the partial crystallization is attributed to the lower concentration of glass formers and the lattice matching between the overlayer and the Ru layer below. [ABSTRACT FROM AUTHOR] more...