Nonmagnetic Intermediate Layer Research Articles

The influence of the interlayer on the magnetic and structural properties of three-layer systems

This article is dedicated to the influence analysis of the thickness and composition of nonmagnetic intermediate layers, tNM, on the magnetic and structural properties of Co/Mo/Co, Co/Si/Co, Co/Bi/Co and Fe1/PDP/Fe2 thin-film systems, as well as comparing the mechanisms of exchange interaction between ferromagnetic, FM, layers through NM spacers. The thicknesses of Co layers are equal to 5.0 nm and the thickness of Fe layers is varied from 14.0 to 50.0 nm. The thickness of NM layers, depending on its composition, is changed from 0.2 to 50.0 nm. It is found that the hysteresis loops for some samples measured in a magnetic field applied parallel to the easy magnetization axis have a rectangular form and for others – more complex two-step ones. The saturation field, HS, of Co/Mo/Co, Co/Si/Co and Co/Bi/Co samples oscillates in magnitude. These data are explained by the presence of exchange coupling between the Co layers through a NM spacer. Fe1/PDP/Fe2 samples have a two-step hysteresis loops, which at tPDP ≥ 10 nm are explained by the exchange coupling between the Fe layers through the PDP layer, and at tPDP > 10 nm - by the magnetostatic interaction between the Fe layers due to the difference in their thickness.

Writability Improvement in Perpendicular Recording Media Using Crystalline Soft Underlayer Materials

Perpendicular recording media technology faces limitation in the writability of media with high anisotropy. Therefore, alternative methods are sought to overcome this problem. Heat-assisted magnetic recording may give rise to high areal densities, but the technological process will take time. We have studied methods to improve the writability in perpendicular recording media using crystalline soft underlayer (C-SUL) materials with fcc(111) texture. One of the recording media designs consists of a simple insertion of C-SUL material between the nonmagnetic intermediate layers, thus providing a path for magnetic flux during the writing. In the alternative methods, part of the nonmagnetic intermediate layer material was replaced with C-SUL material. Overwrite improvement was observed in both the cases, indicating that the C-SUL material will play a major role in improving writability in recording media.

Small, highly oriented Ru grains in intermediate layer realized through suppressing relaxation of low-angle grain boundaries for perpendicular recording media

Through analyzing the growth mechanism of the Ru layer in a nonmagnetic intermediate layer (NMIL) for perpendicular magnetic recording media, a concept for the NMIL is proposed in order to realize a recording layer of small, highly c-plane oriented grains with no intergranular exchange coupling. It was found that (1) fast Fourier transform analysis of plan-view transmission electron microscopy lattice images of Ru layers revealed that hexagonal close packed Ru grains in a c-plane oriented film readily coalesce with each other due to the disappearance of low-angle tilt boundaries. (2) A promising candidate for a NMIL consists of three individual epitaxially grown functional layers: a large-grain seed layer with a highly oriented sheet texture, a first interlayer of small grains, and a second interlayer of nonmagnetic grains isolated by a segregated oxide. (3) The Ru–SiO2/Ru/Mg NMIL based on the proposed concept exhibited small (diameter: 4.8 nm) Ru grains while retaining a narrow orientation distribution of 4.1°.

A novel crystalline soft magnetic intermediate layer for perpendicular recording media

In order to improve the recording efficiency in current perpendicular recording media, it is important to reduce the distance from the head to soft underlayer. In this paper, a soft magnetic intermediate layer is proposed to partially replace the presently used Ru intermediate layer. The new soft magnetic intermediate layer serves two purposes, which are as follows: (1) to decrease the thickness of the nonmagnetic Ru intermediate layer by providing a proper crystalline texture and surface morphology for the optimal crystalline grain growth of the magnetic storage layer on top and (2) to act as an additional soft magnetic underlayer that is closer to the head air bearing surface to enhance the recording performance. The prototypes of the soft magnetic intermediate layer consists of CoIr:SiO2/CoPt:SiO2/NiW multilayer structure. CoIr and CoPt were chosen because both have the hcp structure but the opposite sign for K1. A zero effective magnetoanisotropy of a composite grain is accomplished by varying the thickness ratio of each layer of CoIr and CoPt. The developed multilayer film shows the hcp (00.2) orientation with a dome morphology for facilitating the growth of the top magnetic storage layer as well as soft magnetic properties (K1=6.8×105 erg/cc).

Ultrahigh-density (001)-oriented FePt nanoparticles by atomic-scale-multilayer deposition

Highly ordered (001)-oriented FePt nanoparticles (NPs) with controllable sizes and well-aligned easy axis were obtained by tuning the total layer number n of atomic-scale [Fe/Pt/SiO2]n multilayers deposited on SiO2∥Si substrates. After annealing at 700 °C, the ordered FePt NPs with a small particle size of 5.5 nm (an extremely high areal density of 1.2×1013dots/in.2), a large out-of-plane coercivity of 28.5 kOe, and a narrow size distribution of 13% were attained. All NPs were embedded in the SiO2 substrates, resulting in a flat top surface. Finally, a full-stack film structure of perpendicular recording media composed of FePt NPs (recording layer), SiO2 (nonmagnetic intermediate layer) and CoZrTa (soft underlayer) was demonstrated.

Topological bumped surface induced by the lattice extension of the RuCr intermediate layer for granular-type perpendicular recording media

Surface roughness caused by the grain growth of the RuCr non-magnetic intermediate layer (NMIL) was evaluated using the X-ray total reflection method. In the case of Ru NMIL, the value of root mean square roughness of NMIL ( σ) increases from 0.59 to 1.45 nm with increase in Ar gas pressure and/or thickness of the Ru layer. Judging from the loop slope and normalized coercivity, the degree of magnetic isolation increases as σ increases, independent of the Cr content of a RuCr NMIL. Furthermore, it was found that σ of NMIL is strongly correlated with wettability to the seed layer material and is enhanced by the lattice extension of NMIL.

Advanced granular-type perpendicular recording media

We introduce our recent experimental results for three blocked layers for currently used perpendicular recording media; a recording layer (RL: for recording), a soft magnetic underlayer (SUL: magnetic flux path in writing), and a nonmagnetic intermediate layer (NMIL: underlayer of RL and separation layer between RL and SUL). For the NMIL, uniaxial crystallographic symmetry is an essential requirement for suppression of variant growth of magnetic grains in granular-type RL. From this view point, AlN with wurtzite structure and materials with pseudo-hcp structure, which means fcc structure with stacking faults, were found to be effective. For the SUL, disordered hcp CoIr with negative K u were found to well suppress both spike noise and track erasure due to a wide distribution of magnetic flux under the return yoke in writing and formation of a Neel wall instead of a Bloch wall in the SUL. For the RL, positive-/negative- K u stacked media with incoherent switching mode was found to be effective in order to solve the recent write-ability problem for high K u RL material with high thermal stability. Applying all these items, an advanced medium concept with the stacking structure of “CoPtCr-oxide/CoIr-oxide/CoIr/pseudo-hcp nonmagnetic layer/substrate” is very promising from the view point of (1) switching field reduction of a RL with high K u material, (2) conventional amorphous SUL free, and (3) conventional NMIL free.

Control of Interfacial Structure for Granular Type Perpendicular Magnetic Recording Media

For realizing perpendicular magnetic recording media (PRM) for hard disk drive (HDD), precisely controlled fabrication technology with angstrom scale according to the required properties is essential from material, processes, and physical view point. PRM presently consist of three functional parts; a soft magnetic underlayer (SUL), a nonmagnetic intermediate layer, and a recording layer (RL). The control of domain structure through interlayer coupling induced by RKKY-like interaction in SUL and narrower size distribution of the magnetic particles with magnetically decoupling in recording layer are indispensable for advanced PRM with high signal to noise ratio and thermal stability. In this paper, structure and magnetic properties for SUL and RL in a real fabricated PRM is discussed in connection with sputtering process parameters and also target materials.

Pseudo-hcp nonmagnetic intermediate layer for granular media with high perpendicular magnetic anisotropy

Materials with the hexagonal close-packed structure (hcp) and the face-centred-cubic structure with stacking faults (pseudo-hcp) are examined for the nonmagnetic intermediate layer (NMIL) in order to suppress variant growth of magnetic grains for granular-type perpendicular recording media. Judging from the analysis of the epitaxial growth of Co-based magnetic grains, it has been found that a lattice misfit between NMIL and magnetic grain of less than 6% and a spreading coefficient of wettability of magnetic grain on NMIL of greater than 0.3 J m−3 are required for the recording layer to have high perpendicular magnetic anisotropy energy.

Improvement of magnetic properties of granular perpendicular recording media by using a fcc nonmagnetic intermediate layer with stacking faults

Various binary systems are investigated as face-centered cubic (fcc) bases for the nonmagnetic intermediate layer (NMIL) in granular perpendicular recording media. Loss of stacking order on the (111) plane in fcc NMIL is found to enhance the perpendicular magnetic anisotropy energy (KuRL) of the overlying medium. One persuasive reason for this enhancement is the preferred epitaxial growth of magnetic grains on only the (111) atomic terrace of the fcc NMIL due to collapse of the sixfold symmetry of (1¯11), (11¯1), and (111¯) atomic terraces of the fcc NMIL.

Thin-film recording media on flexible substrates for tape applications

Co-based alloys were investigated as candidates for sputtered thin-film magnetic tape media. Magnetic media on polymeric substrates having acceptable magnetic properties were obtained by applying NiAl/CrMn underlayers prior to CoCrPt deposition with a nonmagnetic CoCrTa intermediate layer. Typical sputtered tape media deposited on traditional polymeric substrates at room temperature revealed sideband modulation noise and large intergranular exchange coupling. A substantial improvement in surface roughness by utilizing smooth polymeric substrates eliminated this modulation noise and accounted for the signal dependent broad-band noise power. This suggests that transition noise is a dominant component of medium noise in sputtered tape media. Additionally, substrate bias is shown to be effective in producing grain decoupling that is necessary for good signal-to-noise ratio.

Effect of non-magnetic intermediate layer on film structure, magnetic properties, and noise characteristics of FeCSi soft magnetic multilayers

The film structures, magnetic properties, and noise characteristics of soft magnetic multilayers with alternately stacked FeCSi soft magnetic layers and non-magnetic intermediate layers were investigated. The FeCSi layers in an as-deposited multilayer with C or Ta intermediate layers had the same nano-sized fine crystalline grains and low media noise as an as-deposited FeCSi monolayer. Amorphous C intermediate layers suppressed the amplitude of spike noise especially well. In contrast, FeCSi layers in an as-deposited multilayer with Cr or Ti intermediate layers were composed of coarse crystalline grains, which increased the media noise. The crystallographic match at the interface between the layers in a multilayer could explain these phenomena. The similarity of the atomic arrangement at the interface between layers and the crystallographic match of less than a few percent for the distance between atoms crystallized FeCSi layers with nano-sized fine crystalline grains into ones with coarse crystalline grains during deposition.

Suppression of Spike Noise from FeCSi Film for Backlayer of Double-Layered Perpendicular Magnetic Recording Medium

The relationships among magnetic properties, noise characteristics, and structures of FeCSi laminated films developed as soft magnetic backlayers of double-layered perpendicular magnetic recording media were examined to find a way to suppress spike noise. FeCSi laminated films were fabricated by alternately stacking soft magnetic layers with non-magnetic intermediate layers. The periods of the cross-tie walls in FeCSi monolayers lengthened as the film thickness decreased. The periods of the cross-tie walls in the laminated films were longer than those in the monolayers. This indicated that the lamination technique was effective in preventing free poles from forming on the surface of the laminated films and that amplitudes of spike noise from the laminated films should have been suppressed. By using FeCSi soft magnetic layers with a thickness of 20 nm and carbon intermediate layers with a thickness of 5 nm, amplitudes of spike noise from the laminated films were suppressed sufficiently for practical use. The laminated films had a high saturation magnetization of 1.6 T and low media noise that was on the same level as in conventional longitudinal magnetic recording media.

Low-noise CoCrPt/FeTaC double-layered perpendicular media with NiTaZr intermediate layer

The effects of a non-magnetic NiTaZr intermediate layer between a CoCrPt recording layer and an FeTaC soft-magnetic underlayer on magnetic and noise properties have been investigated. Introducing a 2-nm-thick NiTaZr layer significantly increased perpendicular coercivity H c and squareness SQ due to the enhanced c-axis vertical orientation of the CoCrPt layer. A medium with a NiTaZr intermediate layer had lower noise properties than the one with a conventional TiCr intermediate layer, apparently due to the improved initial growth of the CoCrPt layer.

MFM study of magnetic interaction between recording and soft magnetic layers

Magnetic force microscopy was used to study the magnetic interaction between the recording and the soft magnetic layers in double-layer perpendicular media by observing the magnetization structure from the soft magnetic layer side. There was a strong magnetic interaction between the recording and the soft magnetic layers. Introducing a thin nonmagnetic intermediate layer between the two layers greatly reduced the magnetic interaction and drastically reduced the medium noise.

Optimization of the writing and erasing characteristics of MO tri-layered films using the non-magnetic intermediate layer

Exchange coupling of tri-layered films using the non-magnetic intermediate layer had been studied. Based on the magnetization reversal mechanisms of exchange coupled double-layered (ECDL) films, the exchange coupling energy was calculated. Temperature dependence of the exchange coupling energy was discussed. Furthermore, influence of the thickness of the intermediate AlN layer on the exchange coupling energy was studied in detail. The results showed that the exchange coupling energy could be adjusted by variation of the thickness of the AlN layer. Finally, the writing and erasing characteristics of TbFeCo/AlN/DyFeCo films has been proposed.

The micromagnetics of periodic arrays of defects in trilayers with interlayer exchange coupling (abstract)

A significant loss in the giant magnetoresistive signal of magnetic stacks with antiferromagnetic coupling across nonmagnetic intermediate layers is caused by regions with a ferro- rather than an antiferromagnetic coupling. The impact of these ferromagnetic coupling regions extends itself into the lateral direction due to the bulk exchange coupling. The present micromagnetic model provides a tool by which a detailed quantitative evaluation of the impact of periodic arrays of parallel line defects is possible. These defects have deviating exchange-coupling constants, and/or anisotropy constants or directions, bulk exchange constants, saturation magnetization, etc., in specific regions. Previously, we developed a phenomenological model of trilayers with two magnetic films separated by a nonmagnetic interlayer that contains one such defect. This model, with a relatively small number of free parameters, allows one to trace complete hysteresis curves. A large number of mode branches reveal themselves and jumpwise transitions between these modes frequently occur along the hysteresis loops. The present micromagnetic model requires a sufficiently accurate assessment of the starting magnetization configuration in order to get a convergence of the code. In general, the micromagnetic code is not capable of overcoming the above irreversible mode conversions. The mode branches evaluated by the phenomenological model are applied to provide the micromagnetic model with appropriate starting configurations after meeting a situation of nonstability. The micromagnetic theory of Brown constitutes the basis of the present approach. The micromagnetic effective field is calculated at grid points and the torque exerted by it on the magnetic dipole is made zero at each grid side by an iteration scheme. The long ranging magnetostatic fields are given by convolution integrals and are evaluated in the Fourier space by using two-dimensional fast Fourier transforms. The single defect is micromagnetically studied by zero padding techniques. Depending on the course of the external field, two different wall regions reveal themselves, to wit, the wall core and the so-called Néel tails. These tails were not incorporated into the phenomenological model. Provided that the defects are sufficiently wide spaced, the agreement between both models is rather good in the core regions. The impact on the GMR signal, in particular of the Néel tails, will be discussed with emphasis on systems with weak interlayer coupling, e.g., the decoupled systems.

Recording medium that can be magnetized vertically and method for manufacturing same

A recording medium which can be magnetized vertically contains a plate-shaped carrier body of nonmagnetic material of which at least one flat side is provided with a thin nonmagnetic intermediate layer having a very smooth surface, to which at least one magnetic recording layer of a material is applied, the axis of easy magnetization of which points in a direction perpendicular to the surface of the medium. The surface of this intermediate layer should be capable of being made smooth in a relatively simple manner. The intermediate layer comprises a glass plate, preferably of fused silica or silicate glass, which is cemented to the carrier body. For the carrier body, particularly a high-strength hardened Al-alloy can be used.

Magnetic transducer head utilizing magnetoresistance effect

In the MR magnetic head of the present invention, its sensing element (2) comprises a plurality of superposed magnetic layers (4,5) having magnetoresistance effect in at least one of them and a nonmagnetic intermediate layer (3) sandwiched therebetween, and a sensing current (i) is fed to flow in the sensing element (2) in the same direction as a signal magnetic field applied to the element. Each of the magnetic layers (4,5) is so formed as to have an easy axis of magnetization substantially perpendicular to the signal magnetic field or to have an isotropic magnetic characteristic in the magneticfilm plane, thereby avoiding generation of Barkhausen noise with certainty.

Multilayered Co-Cr films with non-magnetic intermediate layers by FTS system

Multilayered Co-Cr films with non-magnetic intermediate layers have been successfully prepared aiming for the formation of the Co-Cr film with uniform microstructure throughout the whole thickness of the film. The films were prepared on glass, Si wafer, and polyimide substrates by sputtering 21at%Cr-Co alloy targets using Facing Targets Sputtering (FTS) system. It has been confirmed that Co-Cr 2000-Å-thick multilayered films with carbon intermediate layers are composed of fine spherical Co-Cr particles and are uniform throughout the whole thickness of the film. The c-axes of hcp crystallites in each Co-Cr 200-Å-thick layer in the film are well oriented resulting in a strong perpendicular magnetic anisotropy as a whole when the thickness of the intermediate layers is 50 ∼ 100 Å. This result implies that such control of the microstructure in the Co-Cr films may be useful for preparing suitable media for ultra high density perpendicular magnetic recording.