High-density Magnetic Recording Media Research Articles

FePt-Ag Nanocomposite Thin Films with Longitudinal Magnetic Anisotropy

A well-controlled method to fabricate FePt thin films with the (200) texture and longitudinal magnetic anisotropy for high-density magnetic recording media is reported. FePt-Ag nanocomposite thin films with L1(0) ordered FePt grains embedded in an Ag matrix were deposited on the Cr90Ru10/glass by co-sputtering from Ag and FePt targets. The Ag doping suppressed the (001) texture but improved the L1(0) FePt (200) texture. The magnetic easy axis of FePt-Ag thin films changed from perpendicular to longitudinal in direction. In-plane coercivity of the films varied from 0.8 kOe to 6.5 kOe, depending on Ag contents in the films and under-layer thickness. The change from the (001) to (200) texture could be due to the competition of grain-boundary energy and epitaxial-strain energy.

Deconvolution processing for increasing the resolution of magnetic force microscopymeasurements

Magnetic force microscopy (MFM) is a widely used form of scanning probe microscopy(SPM) that is used for obtaining a magnetic image from a surface with nanoscaleresolution. Currently, the resolution of MFM is limited to approximately 20 nm due to thelong-range nature of magnetic interactions between the MFM probe’s tip and themagnetic medium. This paper describes an optimal signal processing solutionto the problem of achieving high resolution MFM with the goal of significantlyexceeding the level at which MFM metrology currently performs, thus providingmetrologists with a means of resolution increase that is believed will enable, forexample, the rapid development of high-density magnetic recording media(>100 Gbit in−2). This is achieved by using focused-ion beam trimming of a conventional tip to create aprobe tip of predictable magnetic characteristics and then, provided that the sample couldbe approximated as a thin-film, using knowledge of this tip’s sensitivity field for performinga deconvolution on the measured signal to better estimate the magnetic state of the surfaceunder study. Stated differently, as the MFM measured signal is modelled as the convolutionof the magnetized surface and the tip’s sensitivity field, we exploit knowledge of the tip’sproperties to increase the resolution of the MFM image. Details of the deconvolutionapproach as well as images resulting from this processing are the focus of this paper.

Magnetic Domain Imaging of Ni Micro Ring and Micro Dot array by Photoelectron Emission Microscopy

The magnetic domain structures of Ni micro ring (the inner and outer diameters are changed in a micrometer region) and micro dot array with different shapes and with a small separation between dots were observed by the combined method of photoelectron emission microscopy and X-ray magnetic circular dichroism. For the micro rings with a large inner diameter, a flux-closure (FC) domain structure tends to appear more easily than for those with a small inner diameter. This means that the FC domain structure of the micro rings with a large inner diameter is energetically more stable than those of the micro rings with a small inner diameter and the disks. After applying an external pulsed magnetic field of about 40 mT in the in-plane direction, each domain structure switched to an almost perfect single-domain structure. Because of the absence of a central vortex core in the ring as compared with the disks, exchange energy decreases substantially. These phenomena are discussed along with the simulation results. For the micro dot array, the interaction between dots was directly observed. Particularly for the circular disks with a small diameter showing FC domains, no interaction is observed due to the lack of stray fields from each disk. On the other hand, dots with multi domain structures interacted. These types of information may provide us fundamental knowledge for designing high-density magnetic recording media.

Synthesis of acicular Fe–Co nanoparticles and the effect of Al addition on their magneticproperties

We have obtained Al(III)-protected Fe–Co metal nanoparticles with acicularshape by thermal reduction with hydrogen from Al(III)–Co(II)-codopedacicular goethite precursors prepared by oxidation with air of aFeSO4 solutioncontaining Al(NO3)3 andCo(NO3)3 precipitatedwith Na2CO3. These precursor particles were smaller ( nm in length) than those prepared by a previously reported procedure, resulting in smallermetal particles ( nm in length) suitable for high-density magnetic recording media in which higherbit-packing densities could be obtained. The location of Co and Al in the goethiteprecursors, as well as in the final metal particles, have been studied for a betterunderstanding of role that these elements play in the microstructural features and themagnetic properties of the final metal particles. It was found that the Al content in theparticle outer layers was enhanced during the reduction process, while cobaltdiffuses toward the inner part of iron nanoparticles forming an Fe–Co alloy. Theincorporation of cobalt helps to increase the magnetization saturation because itavoids corrosion and minimizes the growth of the iron crystals. The presence ofAl(III) in the particle outer layers of the precursors inhibited the growth of ironcrystals and preserved the acicular shape during the reduction process, whichhas a very favourable effect on the coercivity and the squareness of the metalsamples.

FePt Magnetic Recording Media: Problems and Possibilities for Practical Use

AbstractFor Abstract see ChemInform Abstract in Full Text.

High Density Perpendicular Magnetic Recording Media of Granular-type FePt/MgO/Fe-Ta-C double-layers

Granular-type FePt films with perpendicular magnetic anisotropy are obtained on top of Fe-Ta-C magnetic soft underlayer by annealing FePt/MgO multilayers. For high-density perpendicular magnetic recording medium application, the issues regarding the FePt film crystallographic texture, microstructure, chemical ordering and magnetic properties are addressed in this paper. Based on this medium design, double-layered FePt disks are fabricated on 2.5-inch glass discs. The magnetic recordin performances of these disks are evaluated by a spin-stand. The results reveal a close correlation between the disks SNmR recording performance with the initial multilayer structure.

Ｃｏ−Ｍｏ，Ｃｏ−Ｗ膜の磁気異方性と二相分離

Seeking new materials for high-density magnetic recording media, we investigated the magnetic anisotropy and phase separation of Co-Mo and Co-W binary alloy thin films. Both alloys exhibit much larger magnetic anisotropy than does Co-Cr. Thermodynamic calculations on phase equilibria of Co-X (X = Cr, Mo, W) binary systems predict that magnetically induced two-phase separation can occur in these binary alloys as has been experimentally observed in Co-Cr. In fact, their saturation magnetization and Curie temperature are obviously enhanced by annealing or depositing them at high temperatures, suggesting the promotion of two- (ferro/para) phase separation. Microscopic compositional modulation due to the phase separation was confirmed in a Co-Mo film by micro EDX analysis. However, the amplitude of the compositional modulation is much weaker than the thermodynamic calculations, indicating that the miscibility gap is considerably narrowed probably due to large misfit energy at the ferro/para interface or due to very limited diffusion constants of Mo and W.

Preparation and magnetic properties of CoPt and CoPt:Ag nanocluster films

CoPt and CoPt:Ag nanocluster films have been prepared using a sputtering gas-aggregation cluster source. The cluster size can be controlled in a range from 3 to 8 nm. CoPt cluster films are directly deposited onto Si or 7059 glass substrates. CoPt:Ag cluster films are deposited by co-sputtering or by a CoPt cluster layer with a Ag underlayer and an overlayer. Crystal structure, nanostructure and magnetic properties of the samples were characterized by X-ray diffraction, transmission electron microscopy, and magnetometry. The as-deposited cluster films contain the magnetically soft disordered FCC CoPt phase. Tetragonal L1 0 ordering is realized in the films annealed at a temperature above 650°C. The orientation of clusters is generally 〈1 1 1〉. The coercivity increases with increase of annealing temperature and annealing time, and very high in-plane and out-of-plane coercivities have been achieved in both CoPt and CoPt:Ag cluster films after annealing at a temperature of 700°C for 10 min. The effect of Ag addition on the CoPt:Ag cluster films and the atomic ordering process in these films, and their relations to the hard magnetic properties, is discussed. The preparation of cluster films may provide a new method for fabrication of extremely high-density magnetic recording media.

Statistical approach for the optimal deposition of Cr underlayer for SmCo/Cr magnetic films

The quality of sputtered-deposited SmCo/Cr films used for high-density magnetic recording media depends on several sputtering factors of the Cr underlayer. Investigation into the optimal sputtering conditions needs a large number of experiments. So it is desirable to minimise the number of experiments and maximise the amount of information gained from them. The orthogonal design of experiments and mathematical statistical method are considered as effective methods to optimise the sputtering condition of the Cr underlayer for high coercivity of SmCo/Cr films. Using the orthogonal design method, the effects of the four factors, such as the target–substrate distance, the DC power, the sputtering pressure and the sputtering time, were simultaneously investigated by only nine experiments. The optimal condition of the Cr underlayer was obtained. At the optimal condition, the coercivity was promoted to 3.12 kOe. The target–substrate distance, the DC power and the sputtering pressure are very important factors for coercivity values; on the other hand, the effect of sputtering time is not obvious. It can be proved that our orthogonal design of experiment is of 95% confidence.

Statistical approach for the optimal deposition of SmCo layer for SmCo/Cr magnetic films

The quality of sputtered-deposited SmCo/Cr films used for high-density magnetic recording media depends on several sputtering factors of the SmCo magnetic layer. The investigation into the optimal sputtering conditions needs a large number of experiments. The orthogonal design of experiments and the analysis of variance are considered effective methods, which not only minimize the number of experiments but also optimize the sputtering condition of the SmCo layer for high coercivity of SmCo/Cr films. Using the orthogonal design of experiments, the effects of four factors, such as target–substrate distance, DC power, sputtering pressure and sputtering time, were simultaneously investigated by only nine experiments. It is found that target–substrate distance, DC power and the sputtering pressure are very important factors for coercivity, while the effect of sputtering time is not obvious. In addition, the optimal condition of the SmCo layer was obtained. It can be proved that the results of our experiment are at the 95% level.

Advanced Approaches to Functional Glasses

Two key technologies were reviewed to propose effective approaches to functional glasses. One is combinatorial glass synthesis system. The combinatorial glass synthesis system consists of automatic batch preparation apparatus and two types of automatic apparatuses for melting of glass batches in crucibles. The combinatorial system was effective to search new glass forming systems and to speed up preparation of glass samples. The system was useful for the developments of bulk functional glasses based on doping of ions or compounds. The other is a new technique based on anodization of aluminum. The anodic oxidation of sputtered aluminum film on glass surfaces was applied to preparation of alumina nanostructures possessing nanopore arrays on glass surfaces. Oxides or metallic compounds could be introduced into nanopores using sol-gel technique or electrodeposition technique. The introduction of TiO 2 by sol-gel process yielded high performance photocatalysis showing decomposition rate of acetaldehyde higher by about 13 times than that of P-25 commercial high performance TiO 2 powder catalysis. The impregnation of Ni metal into nanopores by electrodeposition gave high density magnetic rod array of about 600 G/inch 2 , suggesting that the process would be applicable to the development of high density magnetic recording media. The new process based on anodic oxidation of sputtered aluminum was very effective to develop functional nanostructure layers on glass surfaces.

FePt Magnetic Recording Media: Problems and Possibilities for Practical Use

FePt with ordered L10 structure is a promising material for high-density magnetic recording media because the material has high magnetic anisotropy energy. The film is considered to show excellent thermal stability. However, the practical use of FePt media is hindered by several problems that must be solved, i.e. decrease of ordering temperature, realization of films with perpendicular magnetic anisotropy, reduction of media noise, and development of writing methods of bits on high-coercive-force media. Among these problems, the former two problems are being resolved, but the problems associated with reducing media noise and developing writing methods still remain unsolved. It is expected that these problems will be solved by introducing new ideas or methods. Hereafter it will be important to form double-layer perpendicular magnetic recording media and to estimate the read and write characteristics of the media.

Magnetic properties of (Pr0.17Co0.83)69C31 nanocomposite films prepared by pulsed filtered vacuum arc deposition

Nanocomposite (Pr0.17Co0.83)69C31 thin films were prepared by pulsed filtered vacuum arc deposition. Rapid thermal annealing was performed at various temperatures in argon. The variations of the structure and magnetic properties of these films with various annealing temperatures were studied systematically. The sample annealed at 700 °C for 1 min shows a large coercivity of 5.2 kOe and a small grain size of 7.8 nm. The overall small negative ΔM of this film indicates that virtually all the Pr0.17Co0.83 grains are isolated single domain particles with only weak dipolar interactions among them. These results indicate that (Pr0.17Co0.83)69C31 nanocomposite thin films would be a promising candidate for high-density magnetic recording medium applications.

Monodispersed spindle-type goethite nanoparticles from FeIII solutions

A new synthetic route for producing monodispersed and single crystal acicular goethite particles with small particle size and a high axial ratio adequate for use as a high density magnetic recording media precursor is reported. It essentially consists of the hydrolysis of alkaline FeIII suspensions in the presence of carbonate by a three-step procedure, the formation of ferrihydrite primary particles, the ferrihydrite dissolution and nucleation of goethite, and the growth of the goethite nuclei. Changing the temperature of heating during ageing achieved a separation of the two last stages. X-Ray diffraction, transmission electron microscopy, infrared spectroscopy and surface area data have been used to determine the mechanism responsible for the formation of goethite particles with controlled size and shape. The best conditions to prepare monodispersed goethite particles have been established. The results show that uniform goethite particles of (a) 60 nm length with an axial ratio of 6 and (b) 230 nm length with a high axial ratio of 10, can be obtained by using an [OH]/[Fe] molar ratio of 0.35 in the initial suspensions with carbonate or sodium hydroxide, respectively. The [OH]/[Fe] molar ratio determines the particle size and elongation by controlling the hydrolysis reaction rate, while the carbonate ions promote a constant [OH] in the solution, keeping the pH around 10 during the entire synthesis process. This procedure, associated with the appropriate temperature control, leads, under certain conditions, to highly homogeneous goethite particles with sizes smaller than those obtained using sodium hydroxide with the same [OH]/[Fe] ratio.

Microstructure and magnetic properties of nanocomposite FePtCr–SiN thin films

[ (FePt) 100−x Cr x ] 100–δ –[ SiN ] δ nanocomposite thin films with x=0–25 at. %, and δ=0–30 vol. % were fabricated on a natural-oxidized Si(100) substrate by dc and rf magnetron cosputtering of FePt, Cr, and Si3N4 targets. The thickness of the films was kept at 10 nm in order to examine the possibility for applying in high-density magnetic recording media. Transmission electron microscopy (TEM) and electron diffraction analyses indicated that the face-centered-cubic (fcc) γ-phase FePt, body-centered-cubic (bcc) Cr, and amorphous SiN coexisted in as-deposited films. The as-deposited films were annealed in vacuum between 350 and 750 °C for 30 min, and then ice-water quench cooling, in order to transform the soft magnetic fcc γ-FePt phase to the hard magnetic face-centered-tetragonal (fct) γ1 phase. Cr was added to inhibit the FePt grain growth, and was observed by TEM and energy disperse spectrum analysis in the grain surface area of FePt grains. The TEM observation indicated that the structure of the film was an amorphous SiN matrix with FePtCr particles dispersed in it. The particle size of FePtCr in annealed film was increased with the annealing temperature but decreased with the increase of SiN and Cr contents. Magnetization measurements indicated that the optimum condition for high-density magnetic recording purpose of the film was found with x=10 at. % and δ=15 vol. %, annealing at 600 °C for 30 min. The average grain size of the FePtCr in this film is about 9.5 nm, the saturation magnetization is 450 emu/cm3, in-plane coercivity is 3.7 kOe, and in-plane squareness is about 0.75.

ＣｏＰｔ‐（Ｃ４Ｆ８）ｎグラニュラー薄膜の磁気特性

We studied CoPt-(C4F8)n granular thin films for use in high-density magnetic recording media. The (C4F8)n matrix in granular film is very hard and flat, and these properties are advantageous for recording media. CoPt-(C4F8)n granular films were fabricated by the facing targets sputtering method with plasma polymerizing reaction. The CoPt alloy was deposited on substrate and the (C4F8)n matrix was polymerized at the same time. After annealing at 300°C, the CoPt-(C4F8)n thin film had a high coercivity of 4.1 kOe. AFM images of the CoPt-(C4F8)n granular thin films indicated that the grain size was decreased by addition of (C4F8)n matrix. It is considered that the CoPt-(C4F8)n granular films has the potential to be used in high-density recording media.

Functional Effects of Carbon-Coated Iron Metal Particles for Magnetic Recording Media

Magnetic particles with finer size, higher coercive force, and lower electrical resistance are required to produce better magnetic recording media. Metal has become one of the most suitable materials for high-density magnetic recording media; however metal particles are chemically unstable and their magnetic properties such as coercive force and saturation magnetization are easily ruined. We have tried carbon coating using a chemical agent to aid the carbon to adhere to the surface of metal particles. The carbon-coated particles become chemically stable and their oxidation is gradual enough to extinguish the ignition point. Magnetic tapes prepared using the carbon-coated metal particles in the recording layer exhibit improvements in both electrical resistance and orientation properties. A decrease in the electrical resistance of about two orders of magnitude relative to conventionally prepared tapes is achieved when about 10% of the particle weight is carbon black. The squareness and orientation ratio are also raised and viscosity is lowered because the dispersibility of these particles in magnetic lacquer is better than that of the uncoated metal particles. Transmission electron microscopy photographs indicate that all of the carbon black is bound to the surface of the metal particles. © 2002 The Electrochemical Society. All rights reserved.

Cluster growth processes by direct simulation monte carlo method

Thin films obtained by cluster deposition have attracted strong attention both as a new manufacturing technique to realize high-density magnetic recording media and to create systems with unique magnetic properties. Because the film’s features are influenced by the cluster properties during the flight path, the relevant physical scale to be studied is as large as centimeters. In this paper, a new model of cluster growth processes based on a combination of the Direct Simulation Monte Carlo (DSMC) method and the cluster growth model is introduced to examine the effects of experimental conditions on cluster growth by an adiabatic expansion process. From the macroscopic viewpoint, we simulate the behavior of clusters and inert gas in the flight path under different experimental conditions. The internal energy of the cluster, which consists of rotational and vibrational energies, is limited by the binding energy which depends on the cluster size. These internal and binding energies are used as criteria of the cluster growth. The binding energy is estimated by surface and volume terms. Several types of size distribution of generated clusters under various conditions are obtained by the present model. The results of the present numerical simulations reveal that the size distribution is strongly related to the experimental conditions and can be controlled.

Prediction of effective elements for magnetically induced phase separation in Co–Cr-based magnetic recording media

Thermodynamic calculations of the magnetically induced phase separation of the hcp phase in Co–Cr-based alloy systems, which is the origin of the compositional modulation observed in magnetic recording media, have been carried out. The magnetic and nonmagnetic terms in the Gibbs energy are evaluated from available thermodynamic data and Miedema’s semiempirical values. It is demonstrated that the phase separation in Co–Cr–X ternary alloys can be classified into four types, depending on the values of interaction energies between Co and/or Cr and X atoms. Existing magnetic data on Co–Cr-based recording media are discussed in terms of the phase stability of the hcp phases. The present calculations would be useful for development of high-density magnetic recording media.

Quantitative noninterferometric Lorentz microscopy

Noninterferometric phase reconstruction based on the transport of intensity equation (TIE) is applied to experimental images for a Permalloy thin film and to a computational magnetization pattern for a high density magnetic recording medium. An alternative derivation of the TIE is given, based on linear image formation theory. A compact formal solution, suitable for numerical computation, is given.