Perpendicular Recording Media Research Articles

Microstructures of hot-pressed Cr–Ti–Cu targets and their film properties for perpendicular magnetic recording application

In this study, the effect of Cr50−0.5xTi50−0.5xCux (x = 0, 10, 20, 30, 40, 50) hot-pressed target on film performance was investigated. By increasing the ratio of Cu, the target strength and anti crack properties showed significant improvements due to the decrease of brittle intermetallic compound. In addition, the target properties were found to affect the performance of sputtering process and its film. During sputtering test, the arcing behavior was significantly suppressed by reducing the incoherent defects of the target. The results of film analysis also showed the advantages with increasing Cu ratio in Cr–Ti–Cu alloy systems, including the decrease on sheet resistivity, intrinsic stress and surface roughness. Moreover, all as-deposited films were clarified as amorphous structures to meet the requirement for perpendicular recording media application, and further analyzed with Ω and δ indices, which were subjected to quasi-chemical energy and the atomic size difference, respectively. Unfortunately, the excessive Cu addition makes a side effect on the corrosion resistance in acid environment. Related results mentioned above were supported by bending strength measurement, X-ray diffraction, scanning electron microscope, atomic force microscope, Twyman–Green interferometer, and four-point probes method.

Model of advanced recording media: The angular dependence of the coercivity including the effect of exchange interaction

We use a micromagnetic model based on the kinetic Monte-Carlo approach to investigate theoretically the magnetic properties of advanced recording media. The model is employed to examine the impact of the magnetostatic and exchange interaction between grains of realistic perpendicular recording media on the angular-dependent coercivity since the exchange field between grains is an important factor in recording performance. The micromagnetic model allows to take the easy axis distribution and the exchange interaction between grains into account. The results confirm the importance of exchange interaction since the variation of coercivity with angle between the applied field and the orientation of easy axis which is perpendicular to the film plane, (θ) is seen to broaden with decreasing exchange field. We show that a two-stage fitting procedure involving the separate determination of the exchange field and easy axis dispersion provides a useful tool for the characterization of media for perpendicular recording and heat assisted recording. We find excellent agreement between previous experimental results and the simulations including exchange interactions leading to estimate of the exchange coupling and easy axis dispersion.

Promotion of Self-Assembly Patterning of FePt Nanoparticles by Tuning the Concentration of Oleylamine/Oleic Acid Surfactants in a Coating Solution

To provide a bit-patterned perpendicular magnetic recording medium consisting of an array of FePt magnetic nanoparticles, the effect of the total dispersant concentrations of oleylamine and oleic acid in a FePt-nanoparticle/toluene coating solution on a self-assembled nanoparticle array with a long-range periodicity on a flat SiO2/Si substrate and two patterned substrates, respectively, was examined. At a surfactant concentration greater than 0.8 vol%, FePt nanoparticles with an average size of 4.4 nm were arrayed in a two-dimensional and hexagonal-close-packed ordered array with 8.3-nm pitches on the flat surface. Self-assembled nanoparticles were arrayed on the bottom surface of the patterned trench, the array exhibited a hexagonal-close-packed structure. Furthermore the line defects in the arrays are caused by the waviness of the trench walls, and the surface roughness.

Effect of Exchange-Coupling on Switching Fields in Magnetic Recording

Increased levels of exchange in a thin-film granular perpendicular recording media generally lead to reduced coercivity. However, this behavior cannot be deduced simply from the mean-field theory. To gain some insights into this behavior, a simple 2-D chain-of-grains model is employed. It can be recognized that the reduction in coercivity is due to the presence of in-plane magnetization and the corresponding in-plane fields that arise at the transitions between magnetized regions. In addition, a comparison is made between the two classical forms for exchange energy, 1-cos $\theta $ and ${\scriptsize {1/2}}\theta ^{2}$ , that link adjacent grains. The latter form is found to have a much larger impact on coercivity and results in a more Kondorsky-like angular dependence.

Effect of Carbon Overcoat Implantation on the Magnetic and Structural Properties of Perpendicular Recording Media

Carbon overcoats play an important role in the corrosion protection of recording media used in hard disk drive technology. For achieving high areal density, there is a need to reduce the magnetic spacing. Since Carbon overcoat thickness is one of the major contributors to the spacing, it is essential to design suitable overcoats that can protect the media even when they are thin. Filtered cathodic vacuum arc (FCVA) has been studied in the past as potential media overcoat. In order to achieve desired property of FCVA carbon, it is essential to apply a suitable bias voltage, which results in an energetic carbon deposition on the magnetic layer of the recording media [1]. We have recently reported the preliminary results of damage caused on antiferromagnetically coupled (AFC) media layer based on XPS and some magnetic characterization techniques [2]. In this paper, we focus our attention on the implantation effects of energetic carbon on the magnetic and structural properties of recording media of two types; AFC and a single layer, in order to gain more meaningful insight on the implantation and its effect.

Developing Biotemplated Data Storage: Room Temperature Biomineralization of L10 CoPt Magnetic Nanoparticles

L10 cobalt platinum can be used to record data at approximately sixfold higher densities than it is possible to on existing hard disks. Currently, fabricating L10 CoPt requires high temperatures (≈500 °C) and expensive equipment. One ecological alternative is to exploit biomolecules that template nanomaterials at ambient temperatures. Here, it is demonstrated that a dual affinity peptide (DAP) can be used to biotemplate L10 CoPt onto a surface at room temperature from an aqueous solution. One part of the peptide nucleates and controls the growth of CoPt nanoparticles from solution, and the other part binds to SiO2. A native silicon oxide surface is functionalized with a high loading of the DAP using microcontact printing. The DAP biotemplates a monolayer of uniformly sized and shaped nanoparticles when immobilized on the silicon surface. X‐ray diffraction shows that the biotemplated nanoparticles have the L10 CoPt crystal structure, and magnetic measurements reveal stable, multiparticle zones of interaction, similar to those seen in perpendicular recording media. This is the first time that the L10 phase of CoPt has been formed without high temperature/vacuum treatment (e.g., annealing or sputtering) and offers a significant advancement toward developing environmentally friendly, biotemplated materials for use in data storage.

Extracting magnetic cluster size and its distributions in advanced perpendicular recording media with shrinking grain size using small angle x-ray scattering

We analyze the magnetic cluster size (MCS) and magnetic cluster size distribution (MCSD) in a variety of perpendicular magnetic recording (PMR) media designs using resonant small angle x-ray scattering at the Co L3 absorption edge. The different PMR media flavors considered here vary in grain size between 7.5 and 9.5 nm as well as in lateral inter-granular exchange strength, which is controlled via the segregant amount. While for high inter-granular exchange, the MCS increases rapidly for grain sizes below 8.5 nm, we show that for increased amount of segregant with less exchange the MCS remains relatively small, even for grain sizes of 7.5 and 8 nm. However, the MCSD still increases sharply when shrinking grains from 8 to 7.5 nm. We show evidence that recording performance such as signal-to-noise-ratio on the spin stand correlates well with the product of magnetic cluster size and magnetic cluster size distribution.

Exchange interaction energy in magnetic recording simulation

Based on a phenomenological theory, micromagnetic simulations and experiments are used to evaluate an improved function for the exchange interaction between magnetic particles in perpendicular recording media. Assuming diluted spin layers in the particle boundary and a gradual rather than abrupt rotation of magnetization between grain cores, the exchange energy is better described by an even power series of θ, rather than a cosine function. The conventional cosine function does not have a restoring torque near θ = π and adjacent grains tend to align strictly antiparallel. In contrast, using a power series of θ, adjacent grains tend to align at a small angle away from θ = π. This gives rise to a small in-plane magnetization component and therefore a distinct peak in in-plane susceptibility is observed around H = 0. From magnetization measurements of a real medium, a peak is observed around H = 0, which matches with an assumption of 2 or 3 spin layers. In some situations, the exchange interaction between discretized cells for numerical calculation is better described by a power series rather than a cosine function.

Synthesis and magnetic properties of (Eu–Ni) substituted Y-type hexaferrite by surfactant assisted co-precipitation method

A series of (Eu–Ni) substituted Y-type hexaferrite with composition Sr2Co(2−x)NixEuyFe(12−y)O22 (x=0.0–1, Y=0.0–0.1) were prepared by the surfactant assisted co-precipitation method. The present samples were sintered at 1050°C for 8h. The shape of the particles is plate-like which is very advantageous for various applications and the grain size varies from 73 to 269nm. The values of saturation magnetization (Ms), remanent magnetization (Mr) and magnetic moment (nB) were found to decrease which are attributed to the weakening of super exchange interactions. The values of in-plane Squareness ratios (Mr/Ms) ranging from 0.41 to 0.65 whereas in case of out of plane measurement it varies from 0.30 to 0.62.The investigated samples can be used in perpendicular recording media (PRM) due to high value of coercivity 2300Oe which is analogous to the those of M-type and W-type hard magnetic.

Effects of La3+–Nd3+ ions and pre-calcination on the growth of hexaferrite nanoparticles prepared by gel to crystallization technique: Non-isothermal crystallization kinetics analysis

This is the first report ever on La3+–Nd3+ doped M-type hexaferrite nanoparticles: SrNdxLayFe12−x−yO19 (0 ≤ x ≤ 1) prepared by citrate precursor using the sol–gel technique followed by gel to crystallization. The substitution effects of ions and molar ratio of Fe3+/Sr2+ on the formation of ferrite phase were examined using powder differential thermal analysis (DTA) technique, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (Mid-IR) and vibrating sample magnetometer (VSM). The present work aim to study the crystallization of binary La3+- Nd3+ doped hexaferrite nanoparticles. DTA technique was employed to investigate the formation of nanocrystalline SrNd0.4La0.4Fe11.2O19 and revealed that the formation of ferrite phase was occurred in steps and crystallization take place by the means of endothermic reactions. The value of activation energy and crystallization temperature has been obtained from DTA data using different non-isothermal methods. XRD and Mid-IR studies have confirmed the formation of ferrite phase. Through this work an optimum calcination condition was established for the synthesis of single phase hexaferrite nanoparticles even after the substitution of binary rare earth elements. Magnetic properties were determined by using a vibrating sample magnetometer. The magnetic results revealed that the synthesized nanoparticles are suitable for perpendicular recording media due to their high coercivity value.

ChemInform Abstract: Crystal Structure, Magnetic Properties and Advances in Hexaferrites: A Brief Review

AbstractReview: 22 refs.

Effective damping factor for CoPtCr-SiO<sub>2</sub> perpendicular magnetic recording medium with partially switched magnetic domains

Effective damping factor for CoPtCr-SiO<sub>2</sub> perpendicular magnetic recording medium with partially switched magnetic domains

Exploratory Experiments in Recording on Sputtered Magnetic Tape at an Areal Density of 148 Gb/in<inline-formula> <tex-math notation="LaTeX">$^{\textbf 2}$ </tex-math></inline-formula>

A sputter deposited CoPtCr-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> perpendicular recording media with excellent orientation was successfully grown on a thin polyamide film. Using 32-channel GMR tape heads and advanced hard-disk drive heads, the recording performance and durability of this media was investigated. These studies demonstrated an unprecedented broadband signal-to-noise ratio of 17 dB at 896 kb/in using a 77 nm-wide TMR reader, corresponding to an estimated 148 Gb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> recording density, and provided a preliminary assessment of durability exceeding current tape media specifications.

Investigations of Stacking Faults in Stacked Granular Perpendicular Recording Media With a High-Anisotropy CoPt Layer

Microstructural investigations of granular perpendicular recording media based on stacked CoPt-alloy layers were carried out using high-resolution transmission electron microscopy (HRTEM). In the structure investigated, a thin layer of CoPt with high Pt concentration was inserted to meet the thermal stability requirements at higher densities. The increase in the coercivity and nucleation field of the sample observed for the insertion of a thin layer of CoPt (3 nm), and the decrease beyond this critical thickness has been explained based on HRTEM studies. HRTEM results indicated that the insertion of thicker CoPt layer causes stacking faults and the presence of fcc phase in the CoCrPt layers on the top. The number of stacking faults and the fcc content in grains depend on the thickness of CoPt layer, indicating that the observed changes in magnetic properties arise due to the microstructural changes.

Magnetic interactions in CoCrPt-oxide based perpendicular magnetic recording media

First order reversal curves (FORC) method has been reported to be an efficient tool to study interaction between grains and layers of magnetic materials. Although a few studies have been carried out on perpendicular recording media in the past, a study on the effect of systematic variation of exchange interaction in granular perpendicular magnetic recording media on FORC contours has not been carried out in detail. Such a study will help to understand the use of FORC better. In this paper, we have made a systematic set of samples in order to study the variation in exchange coupling and its effect on FORC contours. The pressure during the deposition of the second ruthenium layer and the magnetic layer was varied to alter the separation between the grains and hence the exchange interaction between the grains in the CoCrPt-oxide recording layer. In addition, the thickness of Co-alloy cap layer was used as an additional tool to control the exchange interaction between the magnetic grains. The results indicated that the interaction field obtained from the FORC does not vary in a significant manner when the changes in exchange interaction are small. In comparison, the peak intensity of the FORC shows a clear trend as the exchange coupling is varied, making it a more suitable parameter to study the exchange and magnetostatic interactions in systems such as magnetic recording media.

Investigations of stacking fault density in perpendicular recording media

In magnetic recording media, the grains or clusters reverse their magnetization over a range of reversal field, resulting in a switching field distribution. In order to achieve high areal densities, it is desirable to understand and minimize such a distribution. Clusters of grains which contain stacking faults (SF) or fcc phase have lower anisotropy, an order lower than those without them. It is believed that such low anisotropy regions reverse their magnetization at a much lower reversal field than the rest of the material with a larger anisotropy. Such clusters/grains cause recording performance deterioration, such as adjacent track erasure and dc noise. Therefore, the observation of clusters that reverse at very low reversal fields (nucleation sites, NS) could give information on the noise and the adjacent track erasure. Potentially, the observed clusters could also provide information on the SF. In this paper, we study the reversal of nucleation sites in granular perpendicular media based on a magnetic force microscope (MFM) methodology and validate the observations with high resolution cross-section transmission electron microscopy (HRTEM) measurements. Samples, wherein a high anisotropy CoPt layer was introduced to control the NS or SF in a systematic way, were evaluated by MFM, TEM, and magnetometry. The magnetic properties indicated that the thickness of the CoPt layer results in an increase of nucleation sites. TEM measurements indicated a correlation between the thickness of CoPt layer and the stacking fault density. A clear correlation was also observed between the MFM results, TEM observations, and the coercivity and nucleation field of the samples, validating the effectiveness of the proposed method in evaluating the nucleation sites which potentially arise from stacking faults.

Magnetic structure calculations of Ir0.5Mn0.5 over- and sub-layer at Co(001) surface

Density functional theory calculations are performed to investigate the magnetic structure of Ir0.5Mn0.5 chemically alloyed over- and sub-layer at Co(001) surface. Ir0.5Mn0.5 exhibits ferrimagnetic ordering as the ground state for both systems. Alloyed Ir0.5Mn0.5 chemically ordered monolayer is found to be more stable at the surface rather than the sub-surface of Co(001). The magnetic moments of Mn surface atoms, MnI and MnII, in Ir0.5Mn0.5/Co(001) over-layer system are found to be 3.49μB and −3.56μB, respectively with intra-layer antiferromagnetic (AFM) coupling. While the MnI couples ferromagnetically with Co subsurface moment (1.68μB), MnII couples antiferromagnetically. Ir0.5Mn0.5/Co(001) system exhibits a magnetocrystalline anisotropy energy (MAE) of −2.8meV/cell (−0.7meV/Mn atom), in the direction along [001]. The ferrimagnetic surface ordering and the high MAE of Ir0.5Mn0.5/Co(001) are believed to be promising for potential applications in perpendicular recording media.

Effects of temperature on intergranular exchange coupling in L1 FePt thin films

The effects of temperature on intergranular exchange coupling for FePt:X:FePt (X = TaOx, SiOx, Cr) sputtered thin film stacks were investigated. In-plane FePt layers separated by a thin layer of segregant were used as an experimental model for the intergranular region in perpendicular recording media. Magnetic hysteresis was measured for varying segregant thicknesses (0.5 nm–1.5 nm) at varying temperatures (300 K–700 K). Exchange coupling energies were calculated using the reversal field, saturation magnetization, and coercivity. The intergranular exchange coupling energy was observed to be well-behaved, decreasing linearly with increasing temperature to 600 K. TaOx resulted in the lowest exchange coupling energy at any given temperature, while SiOx and Cr showed similar decoupling capabilities. At 600 K and beyond, antiferromagnetic behavior was observed. Exchange coupling was found to be negligible at operating temperatures above 600 K even with as little as 0.5 nm of TaOx segregant or 1 nm of SiOx segregant.

Noise Characterization of Perpendicular Recording Media by Cluster Size Measurements

New methodology to obtain reliable correlation between magnetic cluster details measured using magnetic force microscopy (MFM) and noise in perpendicular recording media is reported. In addition to the ac demagnetized state, which is often studied by several researchers, magnetic clusters were examined at two other magnetic states of the recording medium to obtain details on thermally unstable and relatively nonreversible clusters that would increase noise and bit-error rates. The proposed method was employed to study magnetic clusters of media samples fabricated at different conditions. Measurements on various samples demonstrated that the MFM can be used to understand the thermally unstable and irreversible clusters in a perpendicular recording medium. A direct correlation between the signal-to-noise ratio of the medium measured using spin-stand and magnetic cluster details from MFM images is obtained. The trend can also be used to understand and distinguish the source of noise (such as writing issues or the media microstructure issues).

Wideband ferromagnetic resonance in nanostructured line arrays

AbstractDynamic properties of magnetic nanostructures have recently been intensively studied due to their potential application in high density perpendicular recording media or magnetic sensors. Permalloy nanostructured line arrays have been prepared using interference lithography. The film thickness is of 50 nm for different lattice periods. The anisotropy field can be investigated by various techniques. One of these techniques is the ferromagnetic resonance spectroscopy (FMR) due to the fact that the resonance field depends directly on the anisotropy. Ferromagnetic resonance measurements have been carried out at as a function of frequency from 1 to 10 GHz for magnetic fields up to 10 kA/m. The sample was placed in coplanar waveguide with the sample plane parallel to the magnetic field. The frequency dependence of the resonance field can be used to calculate the magnetization saturation and anisotropy field under suitable approximations. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)