Co-Cr Layer Research Articles

In Vitro Physical-Chemical Behaviour Assessment of 3D-Printed CoCrMo Alloy for Orthopaedic Implants

In this study, a CoCrMo-based metallic alloy was manufactured using a 3D-printing method with metallic powder and a laser-based 3D printer. The obtained material was immersed in a simulated body fluid (SBF) similar to blood plasma and kept 2 months at 37 °C and in relative motion against the SBF in order to mimic the real motion of body fluids against an implant. At determined time intervals (24, 72, 168, 336, and 1344 h), both the metallic sample and SBF were characterized from a physical-chemical point of view in order to assess the alloy’s behaviour in the SBF. Firstly, the CoCrMo based metallic sample was characterized by scanning electron microscopy (SEM) for assessing surface corrosion and X-ray diffraction (XRD) for determining if and/or what kind of spontaneous protective layer was formed on the surface; secondly, the SBF was characterized by pH, electrical conductivity (EC), and inductively coupled plasma mass spectroscopy (ICP-MS) for assessing the metal ion release. We determined that a 3D-printed CoCrMo alloy does not represent a potential biological hazard in terms of the concentration of metal ion releases, since it forms, in a relatively short period of time, a protective CoCr layer on its exposed surface.

Influence of Co-Cr Particles and Co-Cr Ions on the Growth of Staphylococcal Biofilms

In the last decades, hip prostheses with a metal-on-metal (MOM) bearing have been implanted by orthopedic surgeons worldwide. However, concerns are now raised towards the metal particles and degradation products released by MOM-bearings into surrounding tissue, although effects of Co-Cr wear on infection are also unknown. Therefore, we here determine the viable volumes of staphylococcal biofilms formed on polystyrene in the absence and presence of Co-Cr particles and Co-Cr ions. Three clinically derived and two commercially available staphylococcal strains were grown in the presence of 2 mg/mL Co-Cr particles or 1000/500 µg/L Co-Cr ions derived from Co-Cr salts or from particle supernatant, under static and dynamic growth conditions. A dynamic model simulates the conditions that apply for biofilm formation in the human body, as synovial fluid in mobile patients with hip prostheses is in constant motion with accompanying shear rates. Images of 24 h old biofilms were made with confocal laser scanning microscopy and analyzed with the mathematical computer program COMSTAT, yielding the biovolume of a biofilm. X-ray photoelectron spectroscopy was performed on the particles to study their elemental surface composition. Most isolates showed a tendency of reduced biofilm growth in the presence of Co-Cr particles compared to growth during exposure to metal ions, but this was only significant in one strain under the dynamic growth condition (Staphylococcus aureus 7388). Characterization of the outer surface of the particles revealed a Co-Cr oxide layer enriched by Mo relative to the bulk concentration. MOM bearings produce metal particles which were found to possess antibacterial characteristics under dynamic growth conditions. Further research is needed towards the clinical relevance of this finding.

Thickness Dependent Magnetic and Structural Properties of CoxCr1–x Thin Films Evaporated on Si(100) and Glass Substrates

Series of Co(x)Cr(1-x) thin films have been prepared by thermal evaporation onto Si(100) and Corning glass substrates, x ranging from 1 to 0.60, and the magnetic layer thickness from 17 to 220 nm. The dependence of the magnetic and crystallographic properties on the thickness of CoCr layers have been investigated. The chromium content effect on the saturation magnetization of the films has also been examined. Microscopic characterizations of the films, performed with X-ray diffraction (XRD) measurements, infer that all the samples are composed of hcp phase crystallites with good orientation of the c axis showing a (0001) preferred orientation. The grain size increases with thickness. Atomic force microscopy (AFM) observations show very smooth film surfaces, the highest rms value being 18 amgstroms. The saturation magnetization M(s) was found to decrease from 1400 emu/cm3 to a few emu/cm3 as x decreases from 1 to 0.60, for all values of the thickness. In-plane squareness up to S = 0.83 has been observed for the CoCr/Si thinnest film, and S = 0.90 for the Co/Si thinnest film, too. Magnetic Force Microscopy (MFM) study points out the absence of stripe domains equilibrium magnetization structure for the CoCr thin films whereas the thick Co films present a well defined stripe pattern. From the magnetocrystalline anisotropy field H(a) values extracted from the fit of the BLS spectra, we have computed effective magnetic anisotropy factors K(u), as well. Their negative values for the CoCr samples confirm an in-plane magnetic anisotropy for the thin film magnetization.

Tuning the Perpendicular Magnetic Anisotropy of Co-Based Layers in Multilayered Systems

The combination of Pt with Co either in alloy or in multilayer form is widely studied among the potential magnetic media for ultrahigh density magnetic recording. On the other hand the combination of Co with Cr in alloy form is currently providing commercial magnetic media. In an effort to further exploit and benefit from both systems, we fabricated Co(1-x)Cr(x)/Pt multilayers with two adjustable parameters. The first one is the Cr concentration on CoCr layer (x = 0, 5, 30), which modulates segregation effects on Co grains, thus tunes macroscopic magnetic features such as saturation magnetization and coercive field. The second one is the small layer thickness (< or = 0.6 nm) that affects interlayer coupling, perpendicular magnetic anisotropy and magnetization enhancement through spin polarization of Pt atoms in a ferromagnetic environment. The X-ray diffraction patterns verified the existence of multilayered structures following a preferable face-centered-cubic stacking. The Pt thickness and Cr concentration are found to significantly affect the macroscopic magnetic behavior. It is remarkable the fact that, samples present perpendicular anisotropy that scales with Pt thickness and temperature, even in the case of significant Cr concentration (30% in the alloy) when ferromagnetic behavior is expected to diminish according to relevant studies in alloys and in bulk films. Such an effect may be attributed to spin-polarization of Pt interlayers and was evidenced by X-ray magnetic circular dichroism. The spin-polarization of Pt is also the drive for the strong magneto-optic enhancement in the ultra-violet region between 4.5 and 5 eV shown by magnetooptic Kerr spectroscopy.

Temperature dependence of the training effect in exchange coupled ferromagnetic bilayers

The temperature dependence of the training effect is studied in an exchange coupled thin-film bilayer composed of a hard ferromagnetic pinning (CoPtCrB) layer in proximity of a soft ferromagnetic pinned (CoCr) layer. Interlayer exchange shifts the hysteresis loops of the soft layer along the magnetic-field axis. This shift is quantified by the bias field in far reaching analogy to the exchange bias field of conventional antiferromagnetic/ferromagnetic heterostructures. A ferromagnetic domain state induced in the hard layer experiences aging very similar to the training behavior of the antiferromagnetic domain state in conventional exchange bias systems. Training originates from changes in the spin structure of the pinning layer with consecutive magnetization reversals of the pinned layer. Here we perform a detailed investigation of the temperature dependence of the bias field and its training effect. Consecutively cycled hysteresis loops of the soft layer are measured at various temperatures. We also derive a theoretical description of the temperature dependence of the training effect which is in agreement with the experimental data.

Feasibility study of micro‐undulator for T‐ray sources by using FEM

AbstractPossibility of development of micro‐undulator utilizing perpendicular magnetic recording was explored by 2‐D FEM simulation. In the simulation FePt and CoCr layer were compared as an appropriate recording layer of the undulator. Also variation of maximum field and THD with aspect ratio and gap height were simulated so that they should be optimized in a given thickness of recording layer. From both the simulation results and Bitter patterns recorded on FePt/Fe micro‐undulator, the possibility of development of micro‐undulator by utilizing perpendicular recording technique could be confirmed. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Exchange coupling effects in CoCrPt–SiO2/FeCoTaCr composite media for perpendicular recording

The exchange coupled composite (ECC) media consisting of a magnetically hard CoCrPt–SiO2 layer and a magnetically soft FeCoTaCr layer were fabricated as an approach to improve writability. A nonmagnetic CoCr layer with different thickness was inserted between the hard and soft layers to adjust the exchange coupling strength. With proper CoCr thickness, a decrease of coercivity was observed. Transmission electron microscopy (TEM) revealed that the soft/hard stacked grains were magnetically isolated by SiO2 along grain boundaries. Magnetic properties were characterized by vibrating sample magnetometer (VSM). Angle-dependent coercivity indicated that the stacked magnetic grains switched magnetically in a coherent mode. Angle-dependent switching field demonstrated that ECC media had a better tolerance of the angle dispersion than perpendicular media. The switching field decreased with the increase in thickness of the soft magnetic layer. However, the thermal stability factor was kept almost constant (150) until the soft layer was over 3.3 nm.

Reversible hysteresis loop tuning

We utilize antiferromagnetically coupled bilayer structures to magnetically tune hysteresis loop properties. Key element of this approach is the non-overlapping switching field distribution of the two magnetic layers that make up the system: a hard magnetic CoPtCrB layer (HL) and a soft magnetic CoCr layer (SL). Both layers are coupled antiferromagnetically through an only 0.6-nm-thick Ru interlayer. The non-overlapping switching field distribution allows the measurement of magnetization reversal in the SL at low fields while keeping the magnetization state of the HL unperturbed. Applying an appropriate high field or high field sequence changes the magnetic state of the HL, which then influences the SL magnetization reversal due to the interlayer coupling. In this way, the position and shape of the SL hysteresis loop can be changed or tuned in a fully reversible and highly effective manner. Here, we study specifically how the SL hysteresis loop characteristics change as we move the HL through an entire high field hysteresis loop sequence.

Noise subtraction in antiferromagnetically coupled magnetic recording media

We have investigated, both experimentally and theoretically, the media noise of antiferromagnetically coupled (AFC) recording media. In particular, we have studied how the lower-layer magnetic properties affect the media noise of the composite system. We find that AFC media perform well even for intrinsically noisy lower layers, such as soft-magnetic Co or CoCr layers with high intergranular exchange coupling. To understand the experimentally observed behavior, we propose a new concept of noise subtraction in AFC magnetic systems, in which the noise of the lower layer is anticorrelated to and subtracts from the noise in the upper layers and acts as a low-pass magnetic filter of the magnetization state in the upper layer.

Coercivity and magnetization reversal mechanism in ferromagnet/antiferromagnet bilayers: Correlation with microstructure of ferromagnetic layers

Exchange biasing in ${\mathrm{Co}}_{20}{\mathrm{Ni}}_{80}∕\mathrm{Fe}\mathrm{Mn}$ and ${\mathrm{Co}}_{80}{\mathrm{Cr}}_{20}∕\mathrm{Fe}\mathrm{Mn}$ bilayers has been investigated, where the CoCr layers are of granular structure and the CoNi layers are in the form of a single phase. In the above two series of bilayers, the exchange field is proportional to $1∕{t}_{\mathrm{FM}}$ (${t}_{\mathrm{FM}}$ denotes ferromagnetic layer thickness). For $\mathrm{Co}\mathrm{Ni}∕\mathrm{Fe}\mathrm{Mn}$ bilayers, the coercivity and the uniaxial anisotropic field decrease with increasing ${t}_{\mathrm{FM}}$ with a linear scale of $1∕{t}_{\mathrm{FM}}$. Since they are equal to each other, the magnetization reversal process can be described by magnetization coherent rotation and the coercivity enhancement can be explained in terms of a uniaxial anisotropy model. For $\mathrm{Co}\mathrm{Cr}∕\mathrm{Fe}\mathrm{Mn}$ bilayers, however, the coercivity displays unusual behaviors. First, in comparison with that of single CoCr layer films, the coercivity is reduced instead of enhanced. Secondly, it increases with increasing ${t}_{\mathrm{FM}}$. Finally, the coercivity of the bilayers is not equal to the uniaxial anisotropic field. A noncoherent rotation process is proposed to occur during the magnetization reversal process. The different characteristics of the coercivity and magnetization reversal mechanisms in the two series of bilayers result from the different microstructures in the CoNi and CoCr layers. The present work might be helpful to clarify the mechanism for the coercivity enhancement in ferromagnet/antiferromagnet bilayers.

Exchange biasing and coercivity enhancement in CoCr/FeMn bilayers with granular ferromagnet

Exchange biasing is studied in Co80Cr20 (CoCr)/FeMn bilayers with a ferromagnetic material granular CoCr. Unique exchange biasing characteristics closely related to the microstructures and magnetization reversal process of granular CoCr have been observed. Although the exchange field in CoCr/FeMn bilayers is inversely proportional to the CoCr layer thickness, similar to the conventional ferromagnet/antiferromagnet bilayers, the coercivity HC is found to increase with increasing CoCr layer thickness. More importantly, HC of the CoCr/FeMn bilayers is smaller than that of CoCr single layer films.

Improvement of Switching Field in AFC Media by Inserting Ru or CoCr Layers in Stabilizing Layer

The effects of Co insertion at the interface of CoCrPtB-Ru-CoCrPtB AFC media are investigated. Although the exchange coupling constant J can be increased by inserting Co, undesired magnetic properties are observed including reduction of the switching field of the stabilizing layer or reduction of coercivity of the recording layer. We propose a new antiferromagnetically coupled structure with a laminated stabilizing layer composed of CoCrPtB-(Ru or CoCr)-Co, in which Co remains at the interface to enhance J and a nonmagnetic layer Ru or CoCr is used for suppressing interaction between Co and lower CoCrPtB layer. The coercivity of the laminated stabilizing layer decreased and the switching field increases with increasing thickness of Ru or CoCr. Consequently, the insertion of Ru or CoCr can make the magnetization reversal of the stabilizing layer easier.

Biquadratic coupling in antiferromagnetically coupled magnetic recording media

Using spinstand and magnetometry measurements we have investigated the effective coupling between the two ferromagnetic layers in antiferromagnetically coupled (AFC) longitudinal magnetic recording media. For AFC media with soft-magnetic CoCr and Co lower layers we find that the average equilibrium magnetization direction of the lower layer is a function of transition density in the upper layer. In particular for medium-sized bit cells, biquadratic coupling is observed, for which the average magnetization of the lower layer is perpendicular to that of the upper layer.

Origin of the negative giant magnetoresistance effect inCo1−xCrx/Cu/Co(111) trilayers

We present a theoretical study on ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}/\mathrm{C}\mathrm{u}/\mathrm{C}\mathrm{o}$ (111) trilayers, where a transition from positive to negative giant magnetoresistance effect has been observed experimentally, with increasing thickness of the alloyed layer. The theory, based on a recently implemented conductance calculation, reproduces quantitatively this observation, and the effect is found to be caused by alloying effects, due to a virtual bound Cr d state in the majority spin channel of the Co-Cr layer.

Ｒｕ／Ｃｏ−Ｃｒ／Ｒｕ交換結合層で分断したＣｏ−Ｃｒ−Ｐｔ−Ｂ面内記録媒体のノイズ特性

An exchange-coupling layer consisting of a Co-Cr ferromagnetic layer laminated with a thin Ru layer on both sides was employed as a layer separating the recording layers in longitudinal HDD media. The Co-Cr-Pt-B recording layers, which are divided into sections of equal thickness, are ferromagnetically coupled via the antiferromagnetically coupled Co-Cr layer by a function of the thin Ru layers. Because of the separation of the recording layers, a reduction of about 30% in media noise was observed at 400 kFCI, and the thermal stability was the same as or better than that of the conventional type of synthetic ferrimagnetic media (SFM).

Effects of Mn- and Zr-doped CrMo double underlayers on structure and magnetic properties of cocrptb longitudinal media

The addition of 2% Zr into the CrMo underlayer reduced the grain size of the recording layer to 5.33 nm and achieved a narrow distribution of grain size. The addition of 5% Mn into the CrMo underlayer enhanced the crystallographic texture and coercivity. To obtain both advantages of Zr and Mn doping effects, the Zr and Mn doped double underlayer were introduced in longitudinal media. The magnetic properties and microstructures of the recording layers on CrMoMn-CrMoZr and CrMoZr-CrMoMn double underlayers mainly depended on the underlayer adjacent to the CoCr layer, whereas the underlayer on NiP further modified the characteristics of the recording layers. By combining the CrMoMn and CrMoZr double underlayers, longitudinal media revealed enhanced coercivity, small intergranular coupling, and a narrow distribution of grain size.

Improvement of c-axis preferred orientation of CoCr-based thin film with amorphous Si underlayer

In order to improve crystallographic characteristics of CoCr-based thin film as perpendicular magnetic recording media, amorphous Si layers were deposited as an underlayer using a Facing Targets Sputtering apparatus. First, by increasing the film thickness of CoCr, CoCrTa single layer, crystalline orientation and perpendicular coercivity was improved. The CoCrTa thin film showed better crystalline and magnetic characteristics than those of CoCr thin film. As a result of investigating magnetic and crystallographic characteristics of CoCr and CoCrTa magnetic layer on introducing the Si underlayer, it was found that although the 5 nm Si underlayer was very thin, the c-axis preferred orientation of CoCr/Si and CoCrTa/Si doublelayer was improved significantly with amorphous Si thin film.

Co-Cr(-Ta)/Si 이층막의 자기적 특성

In odder to investigate the magnetic properties of CoCr-based bilayered thin films on kind of underlayer, we introduced amorphous Si layer to Co-Cr(-Ta) magnetic layer as underlayer. First, we prepared CoCr and CoCrTa single layer using the Facing Targets Sputtering system to investigate theirs properties. It was revealed that with increasing the film thickness of CoCr, CoCrTa single layer, crystalline orientation and perpendicular coercivity was improved. The CoCrTa thin film showed bettor crystalline and magnetic characteristics than CoCr thin film. As a result of investigating magnetic properties of CoCr and CoCrTa magnetic layer on introducing the Si underlayer, perpendicular coercivity and saturation magnetization of CoCr/Si and CoCrTa/Si bilayered thin film were decreased due to the increased grain size and diffusion of Si atoms to magnetic layer. And they showed constant with increasing the film thickness of Si thin film. However, in case of CoCrTa/Si bilayered thin film, in-plane coercivity was controlled low at about 250Oe. The c-axis orientations of CoCr/si and CoCrTa/Si bilayered thin film showed a good crystalline characteristics as about <TEX>$2^{\circ}$</TEX>.

Thickness dependence of incremental permeability in Mumetal( t)/CoCr bilayers

The thickness dependence of magnetic properties in mumetal( t)/CoCr(500 nm) bilayers for t=700, 1400, and 2100 nm was studied by measuring incremental permeability. In order to induce in-plane magnetic anisotropy, the deposition was performed in a DC magnetic field of 300 Oe parallel to the film plane and the directions of anisotropy in pinned layer were parallel to those in soft layers. Transverse permeability ratio curves showed the symmetric single peak at zero magnetic field and the values were increased with increase in thickness. Longitudinal permeability ratio curves also showed that the single peak and the peak positions were shifted from zero magnetic field, and reduced with the decrease of bias fields generated by CoCr layer. The asymmetric permeability ratio curves are considered as the effect of exchange coupling between the soft magnetic mumetal layer and the pinning CoCr layer.

Hard magnetic CoCr layer in ferromagnetic tunnel junctions

In magnetic tunnel junctions a highly spin-polarizing layer is usually exchange biased by an antiferromagnetic layer, an artificial antiferromagnetic layer system or a combination of both, while the magnetically soft layer is free to rotate. The use of a single layer of a hard magnetic material is rarely investigated up to now. In this paper, we present the electric and magnetic properties of tunnel junctions with a hard magnetic Co 83Cr 17 layer. The soft magnetic electrode consists of either a single Co layer or a Co/Ni 80Fe 20 bilayer. The magnetic anisotropy and coercive field H C of the CoCr layer depend on its thickness and the kind of the bottom layer (Cu or Ta) and can vary from H C=50–700 Oe. It is found that a thin Co cap layer also influences the hysteretic behavior. Furthermore, only small changes after annealing up to 450°C promise a high thermal stability for the application in magnetic tunnel junctions. Measurements of the tunnel magnetoresistance on large area junctions, however, show a strong magnetic coupling of the hard and soft electrodes.