CoCrTa Films Research Articles

A Study of Redistribution Phenomenon of Solute Atoms in CoCrTa and CoCr Perpendicular Recording Films by Annealing

In the previous work1, we have reported Ta addition is effective in increasing perpendicular coercivity of the films with Cr content lower than 17 at% Cr region and not effective in those with higher than 19 at% Cr region. Also the higher coercivity of the CoCrTa films is interpreted as the enhanced Cr segregation than Ta segregation itself. In the present work, we studied the redistributing behaviour of solutes of the as-deposited films by analysing changes of structures and magnetic properties before and after vacuum annealing. It was found that the redistributing atomic species during the annealing is Cr rather than Ta, which is in good agreement with our previous claims that Ta enhances Cr segregation in CoCrTa system.

Magnetic properties and crystallography of double-layer CoCrTa thin films with various interlayers

In this work, the hysteretic properties and remanence curves of double-layer CoCrTa thin films with various interlayers (Al, Cu, Ag, and Cr) are investigated. It is found that the double-layer CoCrTa films with Cu or Ag interlayers have narrower switching field distributions but similar high coercivities, compared with the films with Cr interlayers. To understand the effects of interlayers on the magnetic properties, the crystallography of these multilayer thin films are studied. The results from this work show that Ag and Cu are strong candidates as interlayer materials in multilayer magnetic-recording media. >

Structural characteristics of bias sputtered CoCrTa/Cr films

Crystallographic texture and lattice spacings of bias sputtered CoCrTa/Cr and Co/Cr thin films have been studied by X-ray diffraction. While only an insignificant change in the Co lattice spacing for the Co/Cr films was observed as the substrate bias voltage was increased, the increase in the CoCrTa lattice spacing for the CoCrTa/Cr films was substantial. The CoCrTa films showed nearly unchanged lattice spacings after a vacuum annealing for film stress release. The lattice increase appeared to be linearly proportional to the Ta content in the CoCrTa film. This implies that the Ta atoms tend to substitute randomly onto the hexagonal sites within the CoCrTa crystal grains, and that very little, if any of the Ta segregates to the grain boundaries.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magnetic properties and structures of CoCrTa films for wide range of Cr variation

The authors studied the effects of Ta addition on magnetic properties of CoCrTa films for a wider range of 13-21 at.% Cr and tried to elucidate how Ta addition increases the coercivity. Ta addition is effective in increasing perpendicular coercivity in the films with Cr content lower than 17 at.% Cr region and is not effective in those with higher than 19 at.% Cr region. The higher coercivity of the CoCrTa films is interpreted as the enhanced Cr segregation behavior due to the difference of chemical affinity among the atoms. However, the lower coercivity of the films with large amounts of Ta is attributed to the formation of the amorphous-like structure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Segregation structure of bias-sputtered CoCr/Cr and CoCrTa/Cr films

The dependence of the fine Cr segregation structure in CoCr/Cr and CoCrTa/Cr films on negative bias voltage (V/sub B/) is examined with a high resolution scanning electron microscope. The relationship between the structure and the magnetic properties is discussed. The Cr segregation in the grains is enhanced by a bias voltage of up to -90 V, resulting in an increase in H/sub C/ and M/sub S/. Further increasing V/sub B/ results in the homogeneous distribution of Cr in the grains and an enhancement of the Cr segregation to grain boundaries from the inside of grains and the Cr underlayer. Such microstructural change causes a decrease in M/sub S/ and an increase in H/sub C/. In the case of CoCrTa films, the effect of V/sub B/ is more pronounced than the case of CoCr films, where the Ta atoms also precipitate at grain boundaries. >

A Study on the Magnetic Microstructure of CoCrTa/Cr Film Media, Using Rotational Hysteresis Loss Analysis

Rotational hysteresis loss analysis was carried out for CoCrTa/Cr thin film media fabricated on glass substrate, to evaluate the influence of the microstructure on the media's magnetic properties. H k grain, defined as the magnetic field at which the rotational hysteresis loss vanishes, remained at almost a constant value of about 4.0 kOe, independent of the values of the coercive force. It is considered that H k grain almost corresponds to the magnitude of the uniaxial magnetic anisotropy field of the grains, and that the coercive force is mainly determined by the degree of intergranular magnetic coupling interaction. In all the films examined, H c was mainly determined by the switching of magnetization, independently of the degree of intergranular coupling. Calculated results suggest a possibility that, in CoCrTa films consisting of large grains, the magnetization in each grain changes direction as a result of incoherent magnetization switching.

Effect of microstructural features on media noise in longitudinal recording media

High-resolution transmission-electron microscopy (HRTEM) has been used to analyze CoCrTa, CoCrPt, and CoNiCrPt alloy thin films deposited under similar conditions onto NiP plated Al substrates with a Cr underlayer. Apparent ∼50 nm Co alloy grains observed by bright field TEM are found to be clusters of smaller 10–20 nm grains with a common growth orientation. Subtle differences have also been observed in the stacking fault density, Co alloy fcc phase concentration, lattice mismatch, and grain separation in the films. In particular, HRTEM shows that the CoCrTa film has clear physical separation between the 10 and 20 nm grains, which is not observed in the other media. Despite similar hysteresis loop properties, the signal-to-noise ratio of CoCrTa is 2.3 dB higher than CoCrPt and 4.6 dB higher than CoNiCrPt. Small isolated grains have been shown to improve media noise, as is observed in CoCrTa media.

Magnetic properties and crystal texture of Co alloy thin films prepared on double bias Cr

A double layer Cr film structure has been prepared by sputter depositing Cr on single crystal Si substrates first without substrate bias and then with various substrate bias voltages. Without substrate bias, Cr{200} texture grows on Si at room temperature; thus the first Cr layer acts like a seed Cr layer with the {200} texture, and the second Cr layer, prepared with substrate bias, tends to replicate the {200} texture epitaxially. CoCrTa and CoNiCr films prepared on these double Cr underlayers, therefore, tend to have a {112̄0} texture with their c-axes oriented in the plane of the film. At the same time, the bias sputtering of the second Cr layer increases the coercivity of the subsequently deposited magnetic films significantly. Comparison studies of δM curves show that the use of the double Cr underlayers reduces the intergranular exchange interactions. The films prepared on the Si substrates have been compared with the films prepared on canasite and glass substrates. It has also been found that the magnetic properties are similar for films on canasite and on glass.

Magnetic Properties and Microstructure of CoCrTa/Cr Magnetic Recording Media

High-density recording requires longitudinal magnetic recording media with high coercivity and low noise. We report our studies of magnetic and microstructural properties of high-coersivity CoCrTa films. A coercivity of 2450 Oe has been obtained by applying a high bias voltage to the substrate. Microstructural analysis by TEM and electron diffraction studies revealed that in high-coercivity film c-axes are strongly oriented in the film plane.

Correlations of modulation noise with magnetic microstructure, transition parameter and rms transition variation for CoCrTa and CoNi thin film media

We report the modulation noise, magnetic microstructure, and transition region characteristics of two thin film media (CoCrTa and CoNi). The magnetic microstructure of these films was observed by using scanning electron microscopy with polarization analysis (SEMPA). The rms variation of the magnetization transition across the track was calculated by digitizing the SEMPA image. The same digitized data were used to find a function that would best fit the transition region. The error function gave a better fit for the transition region than the arctan function. The transition parameter was also estimated from the isolated pulse width and this value was comparable to the value obtained from the error function fit. The rms transition variation for the two samples correlate strongly with integrated noise voltage.

In-contact magnetic recording performance of Pt/CoCrTa thin films on glass computer disks

CoCrTa films deposited on fcc Pt and Au underlayers show excellent c-axis orientation. The ‘epitaxial-growth’ mechanism may explain the origin of such an effect. The perpendicular MOKE and VSM coercivity, shape of hysteresis loops and contact recording results of such media are investigated and discussed together with the film structure. A first peak D 50 of 160 kFRPI has been realized by a single-layer Pt/CoCrTa rigid disk using an in-contact MIG head.

ＣｏＣｒＴａ／Ｃｒ薄膜媒体の磁気異方性の評価と磁気特性

Rotational hysteresis loss was analyzed for CoCrTa/Cr thin film media fabricated on glass substrate, to evaluate the infiuence of the microstructure on the media’s magnetic properties. Hkgrain, defined as the magnetic field in which rotational hysteresis loss vanishes, remained at an almost constant value of about 4.0 kOe, independently of the values of the coercive force. It is considered that Hkgrain almost corresponds to the magnitude of the uniaxial magnetic anisotropy field of the grains,and that the coercive force is mainly determined by the degree of intergranular magnetic coupling interaction. In all the films examined, Hc was mainly determined by the switching of magnetization, independently of the degree of intergranular coupling. The calculated results suggest the possibility that, in CoCrTa films consisting of large grains, the magnetization in each grain changes direction as a result of incoherent switching of magnetization.

Microstructure and crystallography of textured CoCrTa/Cr recording media

Transmission electron microscopy (TEM) has been applied to recording media having a 60 nm CoCrTa film and a 75 nm chromium underlayer, which were DC magnetron-sputtered onto a circumferentially textured NiP/Al substrate. Suitable processing conditions provide in-plane magnetic anisotropy with the preferred direction parallel to the texture lines. This paper focuses on TEM techniques which address the preferred crystallographic orientations purported to be responsible for this important magnetic anisotropy. Elongated probe microdiffraction (EPMD) and standard selected-area diffraction (SAD) patterns from cross-section samples show that the bcc chromium underlayer and the hcp cobalt alloy have strong 〈110〉 and 〈11 2 0〉 out-of-plane growth directions, respectively, which result in in-plane orientations of the Cr 〈110〉 axis and the magnetically easy Co alloy 〈0001〉 c-axis. However, the angular spreads of the growth directions are greater perpendicular to the texture grooves than parallel to them, causing similarly greater out-of-plane components of the Cr 〈110〉 and Co alloy 〈0001〉 axes perpendicular to the texture lines than parallel to them. High-resolution plan-view TEM shows that the Co alloy c-axis has nearly random in-plane orientation. Dark field imaging and EPMD of the plan-view sample show locally altered crystallography near texture lines, but suggest that the change is due in part to the growth orientation tilt, not a dramatic, local, preferred in-plane orientation. Combined, these data suggest that the decreased c-axis in-plane component perpendicular to the texture lines is caused primarily by the 〈11 2 0〉 growth direction following the local grooved surface, not the bulk surface, causing the c-axis to be locally titled out of the bulk film plane near the grooves. This crystallographic difference may have implications upon the observed magnetic anisotropy in these films.

Magnetization reversal mechanism evaluated by rotational hysteresis loss analysis for the thin film media

Rotational hysteresis loss analysis has been carried out for CoCrTa, CoNiPt, and CoCrPt thin-film media to evaluate the influence of microstructure on coercive force through the measurement of magnetic anisotropy. In each medium, the magnitudes of H/sub k//sup grain/ defined as a magnetic field where rotational hysteresis loss W/sub r/ diminishes remain almost a constant value independently of the values of coercive force. With increasing coercive force, the magnitude of the coercive force gradually becomes smaller than that of the switching field of magnetization H/sub p/ evaluated by torque analysis. Through the analysis of H/sub k//sup grain/ and H/sub p/, it is suggested that the coercive force in each examined medium is strongly dependent on the degree of intergranular exchange coupling and/or magnetostatic interactions. While on CoNiPt and CoCrPt media coercive force depends on the rotational hysteresis integral, no correlation between them was observed in CoCrTa films. >

Effects of substrate temperature on magnetic properties of CoCrTa/Cr films

The effects of substrate temperature on CoCrTa/Cr thin films were investigated by depositing CoCrTa films on Cr underlayers/sur with various crystallographic textures at both room temperature and elevated temperature. Contrary to the notion that crystallographic textures of [1120] and [1100] are required to obtain high in-plane coercivity (H/sub c/) and low noise in Co/Cr based thin-film media, the present experimental results show that both H/sub c/ and Delta M depend more strongly on the sputter temperature of the magnetic layer than on its crystallographic texture. It was also found that the Delta M of [1101]/sub Co//[110]/sub Cr/ textured films is lower than that of the [1120]/sub Co//[200]/sub Cr /films with similar H/sub c/. This suggests that [1101]/sub Co//[110]/sub Cr /textured media might have better signal-to-noise properties. >

Preferred orientation in Cr- and Co-based thin films and its effects on the read/write performance of the media

This work investigates the formation of preferred crystallographic orientation (PO) in Cr underlayer as well as CoCrTa and CoCrPtTa thin films and its effects on the recording performance of longitudinal media. The results show that the thin-film media with comparable coercivity but different crystalline PO as measured by x-ray diffraction exhibit significant difference in high-frequency signal amplitude, pulse width, and signal-to-noise ratio. To illustrate the effect of PO on parametric performance, CoCrTa/Cr and CoCrPtTa/Cr media were sputtered on different substrates and/or using special sputtering processes to achieve comparable coercivity but different PO in the films. A PO of Cr(200), which normally occurs on the NiP/Al substrates under adequate sputtering conditions, is found to be the key to obtaining a PO of Co(11.0) in Co-alloy media. The consequence of preferred in-plane c-axis orientation is a higher coercivity and better parametric performance of the medium. The formation of PO in the Cr underlayer is found to be related to the substrate material and the oxygen content in the sputtered films. The nonmetallic canasite substrates tend to promote PO of more stable Cr(110) rather than Cr(200). Consequently, this leads to a PO of out-of-plane c axis on the following Co films. The PO of magnetic layer appears to be an important factor in determining the parametric performance of the media.

CoCrTa/Cr磁気記録媒体の磁気特性と微細構造

High-density recording requires longitudinal magnetic recording media with high coercivity and low noise. We report our studies of magnetic and microstructural properties of high-coersivity CoCrTa films. A coercivity of 2450 Oe has been obtained by applying a high bias voltage to the substrate. Microstructural analysis by TEM and electron diffraction studies revealed that in high-coercivity film c-axes are strongly oriented in the film plane.

Effects of substrate temperature and texturing on the magnetic properties and crystallographic structures of CoCrTa/Cr thin film

Bi-layer CoCrTa/Cr films were deposited on textured aluminium or textured NiP-plated aluminium substrate by d.c. magnetron sputtering. The crystal anisotropy and thereby magnetic properties depending on substrate material, substrate temperature and texturing, were investigated. The magnetic crystal anisotropy induced by the mechanical texture on aluminium or NiP/Al substrates along the texture lines for the film deposited at high temperature, were clearly observed, while the film deposited at low temperature shows less prominent anisotropic behaviour. X-ray diffraction analysis indicates a change in the preferred orientation of the chromium and CoCrTa films sputtered on different substrates at different temperatures. It was found that a high substrate temperature was beneficial to the formation of Cr(002) and therefore epitaxial growth of Co(11¯20) on Cr(002) for either aluminium or NiP/Al substrates.

Magnetic anisotropy of sputtered media induced by textured substrate

Thin-film disks sputtered on the textured substrate can have a magnetization easy axis along the circumferential direction. The mechanism responsible for the induced magnetic anisotropy in CoCrTa films has been investigated. The in-plane anisotropic strain (εa) in CoCrTa films deposited on various thicknesses of Cr underlayer were calculated from the lattice constants of CoCrTa(101̄1) in circumferential and radial directions measured by x-ray diffraction. Both the in-plane magnetic anisotropy energy (Kθ) and the in-plane anisotropic strain in the compressive side ( − εa) were observed to increase with the decrease of the thickness of the Cr underlayer. The corresponding calculated magnetostriction constant λ was − 30 × 10−6. This value is consistent with the magnetostriction constant of CoCrTa films measured by three points bending method, thus suggesting that the magnetic anisotropy in CoCrTa films is induced by the anisotropic strain through the inverse magnetostrictive effect.

Crystallography and magnetic properties of CoCrTa films prepared on Cr underlayers with different substrate bias conditions

Thin CoCrTa alloy films on Cr underlayers were prepared on disk substrates by dc magnetron sputtering. The Cr thickness was varied and three bias conditions were used, viz., no bias, dc bias, and rf bias. Film morphology, crystallography, and magnetic properties were studied. Bias was observed to promote Cr 〈100〉 and Co 〈112̄0〉 preferred orientation in the films. The coercivity was observed to increase with increasing Cr thickness. The application of bias was observed to increase the coercivity and coercive squareness, and to reduce the grain size.