High Perpendicular Coercivity Research Articles

Low-temperature growth of perpendicular FePt films

L1/sub 0/ FePt films with high perpendicular coercivity were successfully fabricated by using Cr/sub 65/Mo/sub 15/Mn/sub 20/ underlayers with subsequent forming gas (Ar 95% + H/sub 2/ 5%;) annealing. To adjust the strain energy and the orientation of FePt, Fe and Pt intermediate layers were used. Samples annealed at 275/spl deg/C with thin Pt layers (<5 nm) show relatively small coercivity due to the stabilizing effects from the underlayers. With the increasing thickness of Pt, the strain was locally released and the (111) grains appeared. The nucleation of the ordered L1/sub 0/ FePt phase accompanied the formation of the FePt (111) phase, resulting in a high coercivity but deteriorated perpendicular anisotropy. To maintain the [001] preferred orientation with high coercivity, the sample with a 3.5-nm Pt layer was annealed at 350/spl deg/C. The coercivity as high as 8400 Oe was realized.

Pulse-Reverse Electrodeposited Nanograinsized CoNiP Thin Films and Microarrays for MEMS Actuators

This paper reports on a low residual stress hard magnetic CoNiP alloy electrodeposition technique for microelectromechanical systems (MEMS) applications based on techniques previously developed for CoNiP thin films for perpendicular magnetic recording. Besides electrolyte chemicals, various processing parameters including applied current density, film thickness, electrolyte agitation, electrolyte pH, and temperature are optimized to provide thick films with low residual stress. The resulting hard magnetic CoNiP alloy exhibits a relatively high perpendicular coercivity of around and a high saturation magnetization of . Thick films up to with a low residual stress have been realized using this CoNiP electrodeposition technique. In addition, CoNiP microarrays thick are surface micromachined for the integrations with magnetic MEMS devices. Experimental results confirm that these microarray configurations have a higher coercivity and maximum magnetic energy density, , than thin films in the perpendicular direction.

Magnetic and structural properties of Co–Pt perpendicular recording media with large magnetic anisotropy

A Co–Pt film with large magnetic anisotropy at room temperature deposition was studied in terms of magnetic and structural properties. A high Ar gas pressure deposition of the Co–Pt film with a high crystal orientation could realize excellent magnetic properties such as a high perpendicular coercivity and a large magnetic anisotropy. This deposition technique of the Co–Pt film could form physically isolated and magnetically weak coupled grains. Magnetization reversal mechanism of the Co–Pt film deposited at a high Ar gas pressure was revealed to be a rotational mode, while the Co–Pt film deposited at low gas pressure seemed to be a magnetic domain wall motion.

Fabrication of hard magnetic microarrays by electroless codeposition for MEMS actuators

We report on a new electroless codeposition system for fabricating hard magnetic NdFeB particle–NiP alloy magnets for magnetic micro-electro-mechanical systems (MEMS) actuators. In the newly developed electroless codeposition process, an NdFeB hard magnetic particle, which cannot be independently deposited from aqueous electrolytes, is added to an acidic NiP alloy electroless plating electrolyte. An NdFeB (particle)-NiP (matrix) composite thin film has been successfully obtained using an optimized electroless codeposition technique. In addition, NdFeB–NiP microarrays magnets with a thickness of 20 μm have been realized by surface micro-machining techniques. These micromachined magnets exhibit good magnetic properties such as a large ( BH) max and a high perpendicular coercivity ( H c) that are particularly well suited for magnetic MEMS actuators. This deposition technique is compatible with many MEMS fabrication processes since it does not demand high processing temperatures.

Nanostructured L1 0 Co–Pt thin films by an electrodeposition process

Nanostructured L1 0 Co–Pt thin films with high perpendicular coercivity have been successfully synthesized on the substrate of Pt buffer layer/Cr seed layer/Si(0 0 1) by an electrodeposition process from a novel plating bath containing ammonium tartrate and ammonia solution as complexing agent and by subsequent annealing. Results show that the alloy compositions can be readily controlled by adjusting the metal ions ratio in the plating bath and applied current density. The as-deposited films with nanocrystalline structure contain a disordered face-central cubic (fcc) structure. By annealing above 600 °C, the films with the disordered phase structure transform to L1 0 ordered phase structure. The nanostructured L1 0 ordered Co–Pt thin films exhibit high perpendicular coercivity comparable to traditional magnetic recording media. The present synthesis provides a unique and effective electrochemical means for inexpensively preparing L1 0 ordered Co–Pt thin films as new magnetic recording media from the aqueous solution.

Si-Doping of Co/Pd Multilayers for Improved Signal to Noise in Perpendicular Magnetic Recording Media

Co/Pd-based multilayers have been Si doped in order to enhance their potential for extremely high-density perpendicular magnetic recording (PMR) media. Co/Pd multilayers have high interface-induced perpendicular anisotropy, high coercivity, and high remnant squareness, all of which make them excellent candidates for PMR. Dopants can be utilized to reduce grain size as well as to reduce magnetic coupling between grains via compositional segregation to the grain boundaries. Here, Si was chosen for a dopant because the phase diagrams indicated that Si may migrate to form silicides at the grain boundaries. An additional benefit of Si as a dopant is that it can be detected chemically, unlike the more common dopant B, which is a much lighter element. A significant difference between the current doping and all other doping in PMR media is that Si was added into the Pd layers rather than the Co layers, which keeps the magnetic layer pure and improves the magnetic properties. This media was also made at room temperature, which yields smaller grains and reduces interfacial diffusion. The static magnetic properties of the Si-doped multilayers were very promising as measured by vibrating sample magnetometry: Hc= 5400 Oe, Ms= 160 emu/cm/sup 3/, and /spl alpha/=4/spl pi/dM/dH/spl ap/1. The fact that the latter term was unity suggests that the grains are magnetically decoupled which promises low transition noise. The samples were measured by atomic force and magnetic force microscopy (AFM/MFM) and by X-ray scattering. They were found to have 12-nm grains. In addition, Si-doped multilayer media that were spin-stand tested showed an increase in signal-to-noise ratio of 5 dB compared to high-performing B-doped media.

Two-Step 방식을 이용한 수직자기 기록용 Co-Cr-Ta 박막의 제작

In order to improve c-axis crystalline orientation and high perpendicular coercivity of deposited <TEX>${Co}_77{Cr}_20{Ta}_3$</TEX>perpendicualr recording layer, Two step method was investigated using a Facing Targets Sputtering System(FTS). The </TEX>${\Delta\theta}_50$</TEX> of <TEX>${Co}_77{Cr}_20{Ta}_3$</TEX>recording layer deposited on seedlayer prepared at Room Temperature was as low as <TEX>$5^\circ$</TEX>, while that of the recording layer without seedlayer was about 11<TEX>$^{\circ}$</TEX>. The Two-Step method using <TEX>${Co}_77{Cr}_20{Ta}_3$</TEX>seedlayer prepared at Room Temperature was shown to be very effective in controling the c-axis orientation of <TEX>${Co}_77{Cr}_20{Ta}_3$</TEX> recording layer with thin thickness.

Electrodeposited Co–Pt micron-size magnets with strong perpendicular magnetic anisotropy for MEMS applications

Co80Pt20 cylindrical magnets (height, h=2 μm and diameter, Φ=5 μm and 10 μm) have been succesfully fabricated by electroplating through resist mask onto Cu(1 1 1) seed layer, at current density of 30 mA/cm2. Strong perpendicular magnetic anisotropy was observed owing to the large magnetocrystalline anisotropy, which yielded high perpendicular coercivity (4.7 kOe or 374 kA/m) and retentivity (6.2 kG or 0.62 T). Large energy product (6.52 MGOe or 52 kJ/m3) was achieved which compares favorably with that of bulk ferrites, rendering these structures potential candidates for hard magnetic componenets in MEMS.

Optimization of the Thickness Ratio of Pd/Si Intermediate Layer in Co/Pd Multilayer Perpendicular Magnetic Recording Medium

The effect of the thicknesses of Pd and Si films in the Pd/Si dual intermediate layer on magnetic properties of the Co/Pd multilayer for double-layered perpendicular magnetic recording medium was studied with the aim of developing an ultra-thin intermediate layer for producing fine magnetic clusters in the Co/Pd multilayered film. The magnetic properties were found to be strongly dependent on the ratio of the Pd or Si layer thickness to the total thickness of the Pd/Si dual film. When the ratio of the Pd layer thickness to the total thickness was 0.7-0.8, high perpendicular coercivity and small slope parameter of the major hysteresis loop were attained simultaneously, which resulted from weak intergranular exchange coupling of the Co/Pd multilayered film. In addition, the total thickness of the Pd/Si intermediate layer was successfully reduced to 4 nm, while retaining its high perpendicular coercivity and fine magnetic clusters, by optimizing the thicknesses of Pd and Si layers. Read-write experiments revealed that improvements in reproducing resolution and signal-to-noise ratio of the Co/Pd multilayered media were achieved by the decrease in the intermediate layer thickness.

ＣｏＣｒＰｔ系垂直磁気記録媒体の下地膜による高抗磁力化

The relationship between the magnetic properties of Co-Cr-Pt film and the film’s surface morphology was investigated in terms of the differences in surface free energy and interatomic distance between the Co and the underlayers. It was found that high perpendicular coercivity was obtained in the film structure where it was flat and smooth and grain separation had begun to occur. Moreover, the surface free energy was found to be one of the factors controlling not only the film surface morphology, but also the crystal orientation.

フラッシュアニール法によるＰｔ下地層上の六方晶フェライト薄膜の特性改善

Thin films of various kinds of hexagonal Magneto-plumbite type (M-type) ferrites as magnetic layer with Pt underlayer were prepared using flash annealing process. M-type strontium ferrite with substitution of Sr2+ and Fe3+ by La3+ and Co2+ thin films (LaCo-SrM) and M-type barium ferrite thin films (BaM) on Pt underlayer were prepared by the Facing-Targets Sputtering system. Since the grain size became huge enough because the high substrate temperature, e.g. around 500°C, is maintained particles by excess heating during the deposition. Flash-annealing technique means to anneal the specimen at high temperature above 900°C for a few moments after the deposition of the films at low temperature of 250°C enough for preventing crystallization. Annealing at 900°C for 3 minutes was an appropriate processing condition as a flash-annealing process to attain high perpendicular coercivity Hc⊥ and perpendicular squareness S⊥ ratio in case of BaM with maintaining the grain size as low as several tens nanometers. 30 nm-thick LaCo-SrM films prepared by flash-annealing at 900°C and for 5 minutes exhibited very smooth surface and small particle size about 22 nm. The film revealed large Hc and squareness of 4.5 kOe and 0.75, respectively. Flash-annealing is very useful for preparing the superior magnetic recording media.

ＡｒとＫｒ混合ガススパッタによるＳｒフェライト薄膜の作製

Magnetoplumbite type Sr-ferrite (SrM) thin films with high magneto crystalline anisotropy were deposited on Pt underlayers. It was found that Pt underlayer is effective to enhance crystallization and the c-axis orientation perpendicular to the film plane. In order to get high crystallization and high coercivity and large squareness ratio, high substrate temperature (> 500 °C) and large thickness of magnetic layer (> 50 nm) were required. In this study, SrM/Pt bilayers were prepared using mixture gasses of Ar and Kr as sputtering gas. Ar and Kr mixture gasses was effective to deposit SrM films with high c-axis orientation and better crystallization even though their thickness below 20 nm. SrM layer sputter-deposited using Ar and Kr mixture gas revealed high perpendicular coercivity Hc⊥ around 3 kOe. SrM layer were able to be dethickness below 20 nm, and crystallized at substrate temperature 450 °C.

Fe-Co/Si]/sub n/ multilayers with high saturation magnetization for backlayer of perpendicular magnetic recording media

Summary form only given. A storage layer with high perpendicular coercivity (H/sub c/spl perp//) is essentially required to achieve high recording density with high bit stability for perpendicular magnetic recording media. A new material with large 4/spl pi/M/sub s/ above 20 kG must be developed for a soft magnetic backlayer (BL) beneath the storage layer as well as a writing head material (T. Osaka et al, 1998) for keeping away deterioration of the writing field gradients by saturation of the BL. In this study, (Fe-Co/Si)/sub n/ multilayers with large 4/spl pi/M/sub s/ as well as low coercivity are introduced. Domain structure and soft magnetic characteristic of (Fe-Co/Si)/sub n/ multilayers (ML) were compared with those of the other BL materials to clarify their suitability for BL in perpendicular recording media.

Structural and magnetic properties of CoCrPt perpendicular media grown on different buffer layers

The influence of buffer layer characteristics on the structural and magnetic properties of CoCrPt perpendicular media has been investigated. Thin (∼10–15 nm) buffer layers consisting of Ta/Ru, Ta/Hf, or amorphous (CoCrPt)Ta 25 produced media layers having high perpendicular coercivity of nearly 3 kOe, but the coercivity was only 1.7 kOe when using a Ta/Ti buffer. X-ray diffraction rocking curves showed the highest degree of (0 0 0 2) texture for the Ta/Ru buffer. In-plane diffraction indicated that the Ta/Ru buffer also had the smallest lattice mismatch (5.6%) with the CoCrPt. Cross-sectional transmission electron microscopy showed that the Ta/Ru buffer promoted local epitaxy with the media layer. Amorphous transition regions were observed at the interfaces between the media and the Ta/Hf and Ta/Ti buffer layers. Some small CoCrPt grains were observed at the interface with the amorphous CoCrPtTa buffer.

Preparation of Co–Cr–Pt alloy film with high perpendicular coercivity and large negative nucleation field

The magnetic properties of Co–Cr–Pt thin films for perpendicular magnetic recording media were studied in terms of the film composition. A very high perpendicular coercivity (Hc ⊥) greater than 5000 Oe was obtained at 13–18 at% Cr content and 12–22 at% Pt content. Perpendicular squareness (SQ ⊥) and the maximum nucleation field ( H N) were equal to unity and −2500 Oe, respectively. Co–Cr–Pt double layered medium has also showed SQ ⊥ of unity and large negative H N.

Effects of thin carbon intermediate layer on magnetic and structural properties of perpendicular recording media

CoCrPt/CoCr/carbon films were sputter-deposited on CoTaZr soft-magnetic underlayers and the effects of a carbon intermediate layer on magnetic and recording properties were investigated by changing a heating sequence in sample preparations. A heating process before a CoCr deposition was needed to obtain a high perpendicular coercivity. The carbon diffusion into a CoCr layer during its deposition led to small crystal grains in the CoCr layer and thereby the CoCrPt layer. Consequently, a high perpendicular coercivity was obtained, which was considered due to the change in magnetization process from a wall motion to a coherent rotation. The use of a thin (1–5 nm) carbon intermediate layer was found to be effective to obtain both low noise and high resolution.

Ｐｔ下地層改良によるＢａＭフェライト薄膜の微粒子化

Magnetoplumbite-type BaM ferrite films deposited on Pt under layers have a large perpendicular anisotropy which is enough for the contact type of perpendicular magnetic recording media. Addition of Ta proved thoroughly effective in attaining smaller grain size in BaM ferrite films. By adding 1 at.% of Ta into Pt under layers, we decreased the grain size of those Pt under layers. BaM ferrite films with smaller grain size have higher perpendicular coercivity (3.5 kOe) and greater squareness (0.69). Lower noise level and higher recording density were obtained through this improvement.

Co-Cr-Ta/Pt/Ti垂直記録膜の作製とPt中間層による微細粒子化

Pt/Ti layers were investigated for the under layers of Co-Cr-Ta perpendicular magnetic recording media. The Co-Cr-Ta/Pt/Ti trilayered films exhibited better c-axis orientation and higher perpendicular coercivity than the Co-Cr-Ta/Pt bilayered films. In order to decrease grain size of the Co-Cr-Ta recording layer, a 5-nm-thick Pt interlayer was introduced to compose [Co-Cr-Ta/Pt]n multilayers. We found that the Pt interlayer was effective for decreasing the grain size of the Co-Cr-Ta recording layer without degrading its perpendicular coercivity. The Pt/Ti under layer and Pt interlayer are useful for the development of Co-Cr-Ta perpendicular magnetic recording media.

磁性材料 有機可塑基板上に堆積させたＣｏ含有酸化鉄薄膜

Co-containing ferrite thin films were successfully deposited on organic flexible substrates by the reactive sputtering method using-an electron cyclotron resonance microwave plasma at a temperature lower than 150°C. The ferrite thin films had an amorphous-like structure, perpendicular magnetic anisotropy and high perpendicular coercivity of about 170kA/m. The perpendicular coercivity increased with increasing substrate thickness. Inserting SiO2 underlayer between organic flexible substrate and ferrite thin films enhanced the perpendicular coercivity.

CoCrPtTa single layer perpendicular magnetic recording media with carbon underlayer

Sputter-deposited amorphous carbon was applied as an underlayer for a Co73Cr18Pt6Ta3 single layer perpendicular magnetic recording medium. It is shown that the amorphous carbon underlayer can control the Co [001] preferred orientation of the Co73Cr18Pt6Ta3 magnetic recording layer and that the microcrystalline structure, magnetic properties, and read–write characteristics of Co73Cr18Pt6Ta3 media are greatly dependent on the carbon underlayer thickness. By x-ray diffraction experiments and transmission electron microscopy observations, it was confirmed that the distribution of the c-axis orientation of Co grains becomes broader in the direction perpendicular to the film surface with increasing carbon underlayer thickness. Furthermore, the Co73Cr18Pt6Ta3 medium with a thick carbon underlayer indicated a relatively high perpendicular coercivity of 2800 Oe and an excellent signal to noise ratio in read–write characteristics.