CoCrPt Films Research Articles

Surface and Microstructure Analysis of CoCrPt Film on RuCoCrX (X = Ti, Re) Intermediate Layers

The microstructural and magnetic properties of perpendicular anisotropic CoCrPt films deposited on Ru or RuCoCrX (X = Ti, Re) intermediate layers were studied. The c-axis of CoCrPt grains were promoted by (0002) textured RuCoCr, and RuCoCrX (X = Ti, Re) intermediate layers due to smaller lattice misfit as compared to Ru. The narrower rocking width (Δθ50 = 3.76°) in RuCoCrRe intermediate layer and CoCrPt shows higher out of plane coercivity (Hc = 6.2 kOe), magnetic anisotropy constant (Ku = 6.2 × 106 erg/cm3) and nucleation field (HN = −2.8kOe) as compared to the Ru intermediate layer (Hc = 5.4 kOe, Ku = 5.9 × 106 erg/cm3, HN = −1.6 kOe). The partial intergranular exchange decoupling of CoCrPt grains was observed. The grain boundaries oxides were formed by the residual oxygen in targets and sputtering processes. The minor Cr2O3, CoO, TiO2, ReO3 oxides were investigated by surface analysis. Due to the minor oxides and Cr segregation at grains boundaries, the CoCrPt films present high coercivity. Samples CoCrPt/RuCoCr and CoCrPt/RuCoCrTi present a minimum at 45° but the values are much higher than the ideal Stoner-Wohlfarth theoretical value 0.5 which could be due to fewer natural oxides for magnetic grains separation. In sample CoCrPt/RuCoCrRe, there is an increase of intergranular interaction as indicated by the large asymmetry and the shift of the minimum at lower angles.

Templates as Shadow Masks to Tune the Magnetic Anisotropy in Nanostructured CoCrPt/Ti Bilayer Films

Off‐axis deposition of Ti and CoCrPt films onto lithographically patterned templates has been used to make nanostructures with a lateral thickness variation that allows the tuning of the magnetic anisotropy. CoCrPt rectangles of 1 μm × 725 nm without a thickness variation show an out‐of‐plane easy axis and a single‐domain configuration after demagnetization. On the other hand, rectangles with a thickness variation along their longer dimension show an out‐of‐plane multidomain state, but an in‐plane vortex configuration occurs when the thickness variation is along the shorter dimension. The evolution of the magnetic behavior is understood from the change in both Ti and CoCrPt thicknesses and their effects on the magnetic anisotropy, and provides a simple method for controlling the magnetic state and reversal process of patterned nanostructures.

Domain-wall structure in thin films with perpendicular anisotropy: Magnetic force microscopy and polarized neutron reflectometry study

Ferromagnetic domain patterns and three-dimensional domain-wall configurations in thin CoCrPt films with perpendicular magnetic anisotropy were studied in detail by combining magnetic force microscopy and polarized neutron reflectometry with micromagnetic simulations. With the first method, lateral dimension of domains with alternative magnetization directions normal to the surface and separated by domain walls in 20-nm-thick CoCrPt films were determined in good agreement with micromagnetic simulations. Quantitative analysis of data on reflectometry shows that domain walls consist of a Bloch wall in the center of the thin film, which is gradually transformed into a pair of N\'eel caps at the surfaces. The width and in-depth thickness of the Bloch wall element, transition region, and N\'eel caps are found consistent with micromagnetic calculations. A complex structure of domain walls serves to compromise a competition between exchange interactions, keeping spins parallel, magnetic anisotropy orienting magnetization normal to the surface, and demagnetizing fields, promoting in-plane magnetization. It is shown that the result of such competition strongly depends on the film thickness, and in the thinner CoCrPt film (10 nm thick), simple Bloch walls separate domains. Their lateral dimensions estimated from neutron scattering experiments agree with micromagnetic simulations.

CoCrPt/Ti Perpendicular Media onto Nanostructured Polymer Templates

The fabrication and the study of the magnetic properties of CoCrPt/Ti nanostructures produced by sputtering onto ordered polymer templates are reported here. Samples exhibit a significant out-of-plane component of the magnetization higher than for planar films, and it is stronger for the thicker CoCrPt films, and for nanostructured films with the shorter period ordering. The shape of the polymeric templates plays an important role for the determination of magnetic easy-axis. Magnetic Force Microscopy images of the samples show a single magnetic domain structure with high out-of-plane anisotropy for the samples with longer ordering (480 nm period).

Influence of Pt Doping on Gilbert Damping in Permalloy Films and Comparison with the Perpendicularly Magnetized Alloy Films

Effects of Pt doping on magnetic properties and Gilbert damping are investigated for Ni80Fe20 permalloy films to compare with damping in alloy films containing Pt with a large perpendicular anisotropy. Gilbert damping constant α and g-factor g for (Ni80Fe20)100-xPtx (x = 0–34 at. %) are evaluated from out-of-plane angular variations of ferromagnetic resonance (FMR) linewidth and resonance field with an analysis based on the Landau–Lifshitz–Gilbert equation. Data of angular dependence of the FMR linewidth are fitted reasonably well by a theoretical model without having to take into account any extrinsic influences on linewidth, thereby allowing us to determine precise values of α. The α values show variation with increasing Pt concentration rising by ∼0.06 at a Pt concentration of 34 at. %, which is very close to those in perpendicularly magnetized CoCrPt and FePt film reported recently. Nevertheless, Gilbert damping rate G for the Pt doped permalloy films is smaller than those in CoCrPt and FePt films. These experimental results are discussed with a spin–orbit torque theory.

Effect of Magnetic Film Thickness on the Spatial Resolution of Magnetic Force Microscope Tips

Magnetic force microscope (MFM) tips were prepared by coating commercial atomic force microscope (AFM) tips of 5 nm radius with Co and CoCrPt magnetic thin films varying the thickness in a range of 10–80 nm. The structural and the magnetic properties of coated magnetic thin films were investigated by scanning electron microscopy, AFM, X-ray diffraction, and vibrating sample magnetometry. The tip radius and the film surface roughness increase with increasing the film thickness. With increasing the film thickness, the MFM signal sensitivity increases, whereas the resolution decreases due to increase of tip radius. The MFM observation resolutions of 10 nm and 23 nm are obtained with the tips coated with 20-nm-thick Co and 40-nm-thick CoCrPt films, respectively. The MFM resolution is influenced by both the tip radius and the magnetic moment of coated material.

Early Stage Growth Structure and Stress Relaxation of CoCrPt Thin Films on Spherically Modulated Polymer Surface

Combined study of in-situ stress measurements and atomic force microscopy (AFM) revealed drastic stress relaxation in the CoCrPt and PS(styrene)-PVP(vinyl pyridine) polymer hybrid structure that was closely related to the growth structure of the film. We have observed not only no large initial growth stress at the initial stages of film growth but also twice smaller stress in magnitude with opposite sign in the CoCrPt/PS-PVP/Si sample. The microstructural studies using AFM at the various film growth stages revealed that the film growth structure plays an important role in the stress relaxation mechanism of CoCrPt films on a corrugated polymer surface.

Fabrication of MgO-based magnetic tunnel junctions with CoCrPt perpendicularly magnetized electrodes

The applicability of perpendicularly magnetized CoCrPt films to the MgO-based magnetic tunnel junctions (MTJs) was investigated. For this study, CoCrPt films deposited on the Ru buffer exhibited hcp(0002)-oriented growth by sputtering method using the low substrate temperature of 250 °C, low saturation magnetization of around 360 emu/cm3, and high magnetic anisotropy field of 6 kOe, which is sufficient to retain the thermal stability of the magnetization direction. The MgO-based MTJs with a synthetic ferrimagnetlike structure were fabricated: CoFe was coupled magnetically with CoCrPt through the thin Ru layer. Transport properties with a magnetic field applied perpendicular to the film plane revealed a tunnel magnetoresistance ratio of about 6% at room temperature.

Scaling Behavior of the First Arrival Time of a Random-Walking Magnetic Domain

We report a universal scaling behavior of the first arrival time of a traveling magnetic domain wall into a finite space-time observation window of a magneto-optical microscope enabling direct visualization of a Barkhausen avalanche in real time. The first arrival time of the traveling magnetic domain wall exhibits a nontrivial fluctuation and its statistical distribution is described by universal power-law scaling with scaling exponents of 1.34+/-0.07 for CoCr and CoCrPt films, despite their quite different domain evolution patterns. Numerical simulation of the first arrival time with an assumption that the magnetic domain wall traveled as a random walker well matches our experimentally observed scaling behavior, providing an experimental support for the random-walking model of traveling magnetic domain walls.

Imaging of isolated magnetic cluster switching in thin CoCrPt films

Thin film permanent magnet materials are a vital component of magnetic recording read elements. However, local variations in the magnetic microstructure inherent in such devices can have numerous consequences on the magnetic state of the films. In this study, magnetic force microscopy is used to image the domains in thin nanocrystalline CoCrPt films that are part of a patterned read sensor device. The films were imaged before and after being subjected to stress fields of 1000–2000Oe (less than the sheet-film coercivity of the CoCrPt) transverse to the original magnet set direction. Subtraction of the images reveals that the magnetization of isolated magnetic clusters irreversibly rotates in the film. These data show that the mechanism for net moment rotation in such films is not a uniform grain moment rotation. The change in net magnetization occurs in discrete local moment switching similar to Barkhausen jumps, where moments of weakly coupled grains irreversibly rotate at fields that are lower than the b...

Magnetic reversal phenomena of perpendicular magnetic islands fabricated by block copolymer lithography

Templated block copolymer lithography has been proposed as a method of fabricating patterned magnetic media. This paper discusses the magnetic properties of perpendicular CoCrPt magnetic uniaxial islands in a range of sizes (5–15nm thick, 20–35nm diameter) fabricated by this method. Sputter-deposited films of perpendicular CoCrPt films were patterned in a series of reactive and ion beam etches. The magnetic islands maintain the perpendicular magnetization from the film, but show increased coercivity (800–1650Oe) as compared to the film (150Oe). Time-scale-dependent magnetic measurements show switching volumes (V*) on the order of the physical volume of the dots (∼5000nm3), suggesting that the dots switch their magnetization coherently and independently of each other. Last, we demonstrate selectively removable topographic templates for imposing long-range order to the system.

Investigation of Elemental Magnetic Moments of CoCrPt Films Using X-Ray Magnetic Circular Dichroism

The elemental magnetic moments of Co and Cr in CoCrPt films were investigated using xray magnetic circular dichroism (XMCD). The spin and orbital moments of Co was calculated using the sum rules; it was found that the magnetic moment of Co in CoCrPt films was dominated by spin moment contribution. The total magnetic moment of Co was found to be lower than that of bulk Co. Further, the Cr moment was aligned anti-ferromagnetically with respect to Co, resulting in a decrease of saturation magnetization (Ms) in CoCrPt films.

Effects of Interfaces on the Properties of Nanostructured Ni‐[Cu(II)‐C‐O] and CoCrPt Films

AbstractFor Abstract see ChemInform Abstract in Full Text.

Effects of PS–PVP diblock copolymer topography on the magnetic properties of CoCrPt thin films

AbstractThe magnetic properties and growth structure of Co68Cr18Pt14 thin films deposited on self‐assembled PS21400 (styrene)–PVP20700 (4‐vinyl pyridine) diblock copolymer surfaces were investigated using a magneto‐optical microscope magnetometer (MOMM). The perpendicular magnetic anisotropy as well as the coercivity of 200 Å CoCrPt/PS–PVP/Si(100) films in comparison with 200 Å CoCrPt/Si(100) were distinctly enhanced. An atomic force microscope (AFM) revealed that the enhanced perpendicular magnetic anisotropy and coercivity in CoCrPt/PS–PVP/Si(100) films might be ascribed to the reduction of the magnetic dipolar anisotropy of CoCrPt films having a rough surface arising from spherically modulated PS–PVP surface morphology and preferential deposition of CoCrPt on top of the PVP block. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of ion beam energy on magnetic properties of CoCrPt and CoPt thin films

The magnetic properties of Cr/CoPt and Cr/CoCrPt thin films prepared by ion beam deposition with Xe ions (0.6–1.5 kV) have been investigated. The effect of ion beam energy on the structural and magnetic properties has been studied. A strong dependence of in-plane coercivity on the beam energy was observed and the coercivity increased with beam energy for both CoPt and CoCrPt thin films. With increasing beam energy from 600 to 1500 eV, the coercivity for CoPt thin films increased from 1700 to 2100 Oe. In addition, CoPt thin films have a greater advantage over CoCrPt thin films. A 40% increase in coercivity for CoPt thin films was obtained at the same remanent magnetization-thickness (Mrt) product as compared to CoCrPt. A minimum thickness of 20 Å for the Cr underlayer and 600 eV beam energy were required for constant coercivity and Mrt. X-ray diffraction studies indicated that CoPt(101̄0) texture and in-plane hcp c-axis orientation were enhanced with increased beam energy. The increase of coercivity with beam energy is attributed to an increase in the peak intensity ratio (101̄0)/(0002). The decrease of grain size for CoPt(101̄0) texture with beam energy was attributed to contribute to improvement in coercivity. Compositional analysis using inductively coupled plasma indicated that the Pt content in CoPt thin films increased with beam energy. The increase of Pt content in the thin films accompanied by an increase in the d spacing (lattice constant) improved in-plane coercivity. From magnetic force microscopy studies, lower inter-granular exchange coupling was observed at higher beam energy.

Use of room-temperature bias sputtering to decrease intergranular coupling in magnetic media deposited on polymeric substrates

CoCrPt thin films sputter-deposited on polymeric substrates without explicit heating were investigated as a function of substrate bias. The coercivity and the coercive squareness in the CoCrPt films were strongly dependent on bias voltage. A significant reduction in the coercive squareness S/sup */ from a value near unity was observed with increasing bias voltage, implying a decrease in the degree of intergranular exchange coupling. With the addition of explicit substrate heating, S/sup */ was further reduced, and was associated with a significant improvement of coercivity. This paper presents a possible approach to achieve media with acceptably low exchange coupling deposited at temperatures well below the glass transition temperature of polymeric substrates.

Role of Ag seed layer for CoCrPt/Ti perpendicular recording media

2 nm metal seed layers (M=Al, Cu, Ni, Cr, Ag, Mg, Fe, Co, Pd, Au, Pt, Mo, and Hf) were sputtered to increase coercivity (Hc) and anisotropy (Ku) of CoCrPt/Ti perpendicular recording media. Among them 2 nm Ag seed layer was very effective to increase Hc of (Co78Cr22)100−xPtx/Ti (x=14,20). However, the effect was more pronounced when (Co78Cr22)100−xPtx films became thinner. In addition α [=4π(dM/dH)Hc] decreased when the Ag layer was used. The film thickness below which the seed Ag layer was effective was reduced with decreasing Pt content. However, x-ray diffraction data showed that the Ag seed layer did not promote (002) texture of Ti and CoCrPt layers. In magnetic force microscope observations, domain size was reduced when the Ag seed layer was used. The reason for the higher coercivity of CoCrPt films with the Ag seed layer is thought to be due to change of exchange constant of the grains, for which the grain boundary area plays an important role. Effects of film thickness and Pt content can also be explained successfully by the variation of exchange constant due to grain boundary.

Development of microstructure in Cr and Cr/CoCrPt films made by pulsed laser deposition

Cr films and Cr/CoCrPt bilayer films have been grown using ion-beam-assisted pulsed laser deposition (PLD). High mobility conditions such as a substrate temperature above 350 °C, a low deposition rate, and a high laser energy promote the formation of a {100} bcc crystallographic preferred orientation in the Cr layer, while a {110}-oriented film is formed under other conditions. The {100} orientation can be formed at lower temperatures if the film is bombarded by energetic Ar ions during growth. CoCrPt grows with the hcp-{112̄0} orientation on bcc-Cr {100} underlayers, which is the same epitaxial relationship that occurs in sputtered Cr/Co-alloy films used in hard disk recording media. PLD CoCrPt films also have magnetic properties broadly similar to those of sputtered films. The PLD film microstructure development is interpreted in terms of the preferential nucleation of {100}-oriented Cr crystals during the early stages of film growth.

Origins of substrate-topography-induced magnetic anisotropy in sputtered cobalt-alloy films

Cr(001)/CoCrPt (112̄0) films, used in magnetic hard disks, exhibit in-plane magnetic anisotropy when grown over a substrate patterned with shallow grooves. In this experiment, Cr/CoCrPt films are grown over substrates that have been patterned using lithographic techniques to produce well-controlled topography. The in-plane anisotropy, which is of the order of 104 J m−3, increases with the groove height and frequency. This magnetic anisotropy is a result of anisotropic in-plane crystallographic orientation and anisotropic stress. Stress-induced anisotropy accounts for up to 25% of the total in-plane anisotropy, but the major contribution to the anisotropy is a preferential Co c-axis alignment parallel to the groove direction.

보자력 향상을 위한 Ti/CoCrPt박막의 하지층

20nm이하의 얇은 박막에서도 높은 보자력이 요구되는 Ti/CoCrPt 수직자기기록박막의 보자력 향상을 위해 Al, Cu, Ni, Cr, Ag, Mg, Fe, Co, Pd, Au, Pt, Mo, Hf등의 여러 하지층과 제조조건이 보자력에 미치는 영향을 조사하였다 이들 중 Ag과 Mg하지층은 Ti/CoCrPt박막의 보자력을 향상시켰으며 특히 2nm Ag 하지층을 사용할 경우 10nm CoCrPt 박막에서 2200 Oe의 높은 보자력을 보일뿐 아니라 <TEX>$\alpha$</TEX>값을 낮추는 효과가 있었다. 그러나 Ag를 하지층으로 사용하면 기대와는 달리 Ti(002)면의 우선배향 성장이 전혀 일어나지 않아 보자력 증대에 다른 기구가 작용하는 것으로 판단되었다. 그리고 표면의 거칠기가 큰 기판에서는 보자력뿐만 아니라 역자구생성자계도 감소하였다. Sputtering conditions and various underlayer such as Al, Cu, Ni, Cr, Ag, Mg, Fe, Co, Pd, Au, Pt, Mo and Hf were investigated for coercivity enhancement of 20 nm Ti/CoCrPt thin films in order to increase the coercivity of the films thinner than 20 nm. Among them, Ag and Mg were effective to increase the coercivity. Particularly 2 nm Ag was very effective to increase the coercivity and nucleation field as well as to reduce <TEX>${\alpha}$</TEX> value in CoCrPt thin film such that the coercivity of 2 nm Ag/18 nm Ti/10 nm CoCrPt film was 2200 Oe. However, it seemed that other coercivity enhancement mechanism operated in CoCrPt films because Ti (002) preferred texture was not developed with Ag underlayer contrary to a general expectation. And the coercivity and nucleation field were decreased when glass substrate with rougher surface was used.