Correlation of detailed microstructural information obtained from a temperature series (25–275°C) of otherwise identical CoCrTa/Cr recording media with detailed recording performance measurements demonstrates two mechanisms for magnetic isolation.

Media were prepared by sputter deposition of 75 nm Cr underlayers and 60 nm Co84Cr12Ta4 layers onto circumferentially textured NiP plated aluminum substrates using an Intevac MDP-250 machine.

High-resolution transmission electron microscopy (HRTEM) and high-resolution scanning electron microscopy (HRSEM) show columnar isolation by voiding, via the mechanism of shadowing during low temperature growth. Shadowing decreases with increasing temperature until voiding disappears at 150°C. At high temperature (275°C), large intergranular separation is observed, which has been attributed to elemental segregation. This separation decreases as temperature decreases, until it disappears at 150°C.

Detailed magnetic recording measurements show that the maximum normalized media noise power is observed at 150°C. It decreases as more isolated structures are formed by increasing or decreasing temperature. Uniform magnetization noise, a measurement related to crosstrack correlation length within a magnetization transition also shows this trend.

It is suggested that HRTEM shows two different microstructural features that control magnetic correlation lengths and resulting media noise.

Cross-hatch type texturing has been widely used to replace circumferential texturing in the thin film media industry for optimizing tribology performance. However, higher “cross hatch angle” (CHA) may degrade magnetic performance. The relationship between texturing cross hatch angle (CHA) and magnetic properties and their effects on the read/write characteristics of sputtered thin film media are discussed in this paper. As the CHA increases, both the orientation ratio (OR) and the squareness ratio “S(c)/S(r)” decrease. The film with the highest OR is located at CHA=90, which has the lowest media noise. The medium has highest signal/noise ratio when CHA is equal to 90. PW50 can decrease as much as 4 nanoseconds as CHA increases to 730. By calculating a ratio of the intensity of Cr (110) + CoCrPtTaB (0002) to the intensity of Cr (200), we are able to correlate the intensity ratio to magnetic properties and read/write characteristics.

With the increase of magnetic storage capacity in view, sub grain decomposition in Co-Cr magnetic recording material is examined with the field ion microscope / atom probe (FIM/AP) on a nanometer scale. Concentration variations in sputtered 50 nm Co-20at% Cr and 3 μm Co-22at% Cr films are analysed. Layers with up to 50 nm thickness are sputtered directly onto tungsten FIM tips. FTM-tips of layers with up to 3 μm thickness are prepared by a lithography and etching technique. The measurements show decomposition on the scale of a few nanometers. The concentration amplitudes vary between 11 at% Cr and 42 at% Cr within 50 nm films. Within 3 μm films the concentration varies from about 10 at% Cr to 30 at% Cr. Furthermore, at grain boundaries 3–4 nm precipitates of about 40 at% Cr are observed. The observed concentrations depend on substrate temperature. The compositional inhomogeneity can be explained by a miscibihty gap in the hep phase solid solution which is induced by magnetism at low temperatures.

The internal stress and magnetic properties have been measured for cobalt alloy films deposited using a range of sputter conditions. The sputter conditions affect the internal stress and the microstructure, both of which contribute to the magnetic properties of the films. Stress influences the magnetic properties via magnetostriction, while the microstructural effect on coercivity comes primarily from the degree of separation and size of the grains in the film. The effect of stress on coercivity was investigated separately by applying external stresses to the films, and magnetostriction coefficients were derived for different alloys. The change in coercivity with sputter parameters indicates that in alloys such as Co77Ni7Cr4Pt12, the microstructure has the dominant effect on coercivity.

The effects of grain morphology and crystallography on the magnetic properties of CoCrPt/Cr thin films were investigated as a function of sputtering parameters of CoCrPt thin films. Cross sectional TEM exhibited strong separation of Co grains with increasing argon sputtering pressure, resulting in reduced exchange coupling and increased coercivity. Most Co grains sputtered at high pressure were separated by 10 to 20 Å thick boundaries, possibly due to the enhanced scattering of argon ions by sputtering particles and thus the observed higher content of Pt in the deposited films. The application of substrate bias greatly decreased the Co grain separation and the nonmagnetic grain boundary disappeared by -200 V bias sputtering, resulting in increased exchange coupling. The bias sputtered CoCrPt thin films decreased their grain size and increased epitaxial growth on Cr layer and also (1010) texture. The magnetic field required to saturate the film increased significantly with increasing substrate bias, possibly due to the induced residual stress in the bias sputtered films.

Thin films for magnetic recording are usually deposited on metallic Cr underlayers to control their crystallographic texture and other microstructural features such as grain size and crystal perfection. In this paper, the mechanisms involved in the production of thin films (both underlayers and magnetic layers) with specific crystallographic textures is reviewed and discussed. We first present an overview of a model for the development of the initial crystallographic texture of films grown on amorphous substrates. The textures that various films develop during growth are next discussed followed by a review of the role of epitaxy of Co-alloy films on Cr with underlayers and interlayers. The control of grain size of the magnetic film is also discussed in light of the underlayer grain size. Finally, the role of epitaxy on crystalline perfection and subgrain structure is discussed.

The effects of grain-to-grain epitaxy conditions on the magnetic properties of high coercivity CoCr13Pt13 films with bilayer Cr/Cr, V/Cr and V/V underlayers were studied. V/Cr films were used in order to obtain underlayers that would differ from Cr only by a size of the lattice constant. Introduction of V instead of Cr as an underlayer changed the relative misfits between CoCrPt and the underlayer lattice and increased the amount of {0002} texture in the magnetic film. This effect led to a decrease in the in-plane coercivity. CoCrPt/V/Cr and CoCrPt/Cr/Cr films exhibited similar texture of the underlayer, the same microstructure and similar level of internal stress. Correspondingly the decrease in coercivity did not exceed 10% (from 2.7 kOe to 2.5 kOe). On the other hand CoCrPt/V/V film had more than 4 times smaller coercivity (0.6 kOe). In this case, change in the magnetic properties was caused not only by altered misfits but also by the change in microstructure, texture and state of stress in the film. Results obtained indicate that small changes in misfits between a magnetic layer and an underlayer can be effectively used to control coercivity only if other structural parameters remain unchanged.

The effects of the substrate temperature on the magnetic properties and crystal structure of Co89Cr7Pt4/Cr films deposited by laser ablation were studied. A pulsed KrF excimer laser with a wavelength of 248 nm was focused on ablation targets in a vacuum chamber. The laser irradiation energy was estimated to 10 J/cm2. Cr underlayer and Co89Cr7Pt4 films were successively deposited on the Si substrate at a rate of 0.012 nm/pulse. At a substrate temperature lower than 350 °C, an in-plane coercivity of 30 nm thick CoCtjPu film deposited on 50 nm thick Cr underlayer was 50∼150 Oe showing no significant influence by the substrate heating. The coercivity at 450 °C, however, increased to 800 Oe showing a maximum at this temperature. X-ray diffraction analyses showed that the magnetic films formed at lower than 350 °C have fcc-Co phase, while the films deposited at 450 °C had hep-Co phase with the c-axis oriented parallel to the substrate. At temperatures higher than 450 °C, the coercivity decreased concomitant with a disappearance of the oriented hep-Co phase. The grain size of the films increased from 10 nm to 20∼30 nm by increasing the substrate temperature. The increase of coercivity is probably due to annealing effects resulting in the grain growth of Cr underlayer and the phase transformation of the magnetic films to form the hep-Co phase.

We have studied 100nm thick electron beam evaporated Co1-xNix alloy films in the composition range 0 ≤ x ≥ 1 using magneto-optical spectroscopy and magnetic anisotropy measurements. For films with x ≈ 0.2 we have also investigated the dependence of these quantities on the growth temperature, which was varied in the range 27 ≤ TG ≥ 408°C. Both as function of the Ni content x and the growth temperature TG we observe the anticipated hcp → fcc phase transition, e.g. by monitoring the magneto-crystalline anisotropy constant Ku, 1, which changes continuously from values of ≈ 0.3MJ/m3 for Co rich hcp alloys (0 ≤ x ≥ 0.25) to ≈ -0.05MJ/m3 for Ni rich fcc alloy films, in good agreement with bulk literature data. The new and most striking result, however, is observed in the polar magneto-optical Kerr and ellipticity spectra, which were measured in the photon energy range 0.8 ≤ hv ≥ 5.5eV. Changes by up to about 40% in Kerr rotation for films of constant composition and magnetization are observed when the structure changes from hcp → fcc. This demonstrates the sensitivity of magneto-optical effects to structural changes, making Kerr spectroscopy a useful electronic and physical structure probe.

Layered structures can possess a high volumetric density of interfaces, which can result in novel magnetic properties. We report magnetic characteristics of two types of atomically layered structures, (001) oriented intermetallics with the CuAu(I) crystal structure and (111) oriented artificial multilayers. C-axis oriented superlattices of PtFe, PtCo, PdFe and PdCo with the layered CuAu(I) structure, possess large magnetic anisotropies and novel magneto-optic properties relative to the corresponding random alloys. These films are produced by annealing, with tetragonality and magnetic anisotropy developing in a fashion which depends on the initial bilayer period and annealing parameters. (111) oriented artificially grown Pd/CoCr multilayers are reported for perpendicular magnetic recording applications. Using a perpendicular contact probe transducer, the multilayers exhibit two times the readback signal of CoCr media. The multilayers can be made with low roughness suitable for contact recording, and can generate narrow readback pulses with large amplitude. Many aspects of Pd/Co performance, such as overwrite, can be predictably optimized for a given set of transducer properties. The reported results show that compositionally modulated structures can be made which have a wide variety of useful properties for perpendicular hard disk and magneto-optic recording.

A series of Pt/Co multilayers were sputter-deposited under various deposition conditions to promote structural changes resulting in marked differences in both the perpendicular anisotropy and magnetic coercivity. High resolution transmission electron microscopy was used in combination with other analytical techniques to study the structure of these films. It was found that the most important feature controlling the magnitude of the anisotropy is the interface sharpness. Conversely properties such as the quality of the (111) texture, grain shape or the defect structure, were found to be of secondary importance. The magnetic coercivity ranged from 0.6 to 7 kOe depending on the sputtering conditions and was found to depend strongly on the grain boundary structure rather than on the grain size.

We report magneto-optical recording with 62 dB CNR (carrier-to-noise ratio) at 488 nm for quadrilayer structures comprising polycrystalline CoxPt1-x (x = 0.28) alloy films deposited on ungrooved, silicon nitride -coated glass discs, held at 300°C, by UHV evaporation. The key parameter controlling magnetic anisotropy of the films is substrate temperature during deposition. Polycrystalline films grown on amorphous silicon nitride have a large coercivity and full perpendicular remanance when grown at 300°C. Synchrotron X-ray diffraction data for polycrystalline films grown at 300 and 600°C confirm the presence of short-range compositional order, to the CoPt3-L12 phase in both cases. Such ordering can introduce an anisotropy in the distribution of Co-Co pairs in the alloy and is a possible source of the magnetic anisotropy.

CoCrNi bilayer films with Cr, Ti and Zr interlayers were deposited by DC magnetron sputtering onto ultra densified amorphous carbon substrates and characterized using cross-section transmission electron microscopy and vibrating sample magnetometry. The films are polycrystalline with a columnar microstructure. In the Cr interlayer case there is layer-to-layer epitaxy throughout a given column. Magnetic measurements snowed a simple in-plane easy axis magnetic hysteresis loop. In the Zr and Ti interlayer cases epitaxy within a column was lost beginning with the first CoCrNi/(Zr/Ti) interface, resulting in a magnetic layer consisting of two crystallographically unrelated CoCrNi films. Magnetic measurements revealed a complex step-structure hysteresis loop for this case. Annealing the Zr interlayer film led to a significant growth of the amorphous layer due to a solid state amorphization reaction between the Zr and CoCrNi, which was accompanied by a decrease in the saturation magnetization.

We have produced Co1-xPtX (X = 0.53 and 0.75) alloy films using DC magnetron sputtering and investigated their magnetic properties using vibrating sample magnetometry(VSM) and Kerr hysteresis loop tracer. The as-deposited Co-Pt alloy films show a strong in-plane magnetization. By annealing the alloy samples, we have identified that the magnetic properties are drastically changed. While the magnetic properties of the Co0 25Pt0 75 alloy films show no noticeable changes, the coercivity and the squareness of the Co0.47Pt0.53 alloy films are drastically increased after annealing. Transmission electron microscopy(TEM) and x-ray diffractometry(XRD) analysis showed that CoPt(L10) and Co-Pt3 (L12) ordered phases, respectively, are formed in each case with a strong (11) texture. We suggest that the perpendicular magnetic anisotropy in the Co-Pt system does not depend on the mere textureness of the layer but strongly depends on the arrangement of Co and Pt at an atomic scale.

Magnetic x-ray circular dichroism in x-ray absorption has been used to investigate the ternary multilayer system, Fe Co Pt. Samples were prepared by planar magnetron sputter deposition and carefully characterized, using a variety of techniques such as grazing-incidence and high-angle x-ray scattering, Auger depth profiling and cross-section transmission electron microscopy. As previously reported, the Fe9.5Å Pt9.5Å exhibits a large dichroism in the Fe 2p absorption. Interestingly while the Co9.5Å Pt9.5Å has no measurable dichroism, the Fe4.7Å Co4.7Å Pt9.5Å sample has a dichroism at both the Fe 2p and Co 2p absorption edges. These and other results will be compared to slab calculation predictions. Possible explanations will be discussed.

Giant Magnetoresistance (GMR), crystal structure, and magnetic properties have been investigated in a series of sputtered Ni66Fe16Co18/Ag multilayer films with induced uniaxial anisotropy. The film thickness ranges studied were 20 and 25 Å for NiFeCo, and 25 to 50 Å for Ag. GMR was only evident in the films after post-deposition annealing. This onset of GMR is thought to be due to the breaking up of the NiFeCo layers into ferromagnetic platelets or islands by the immiscible Ag diffusing perpendicular to the film plane along the grain boundaries. The magnitude and field sensitivity of the GMR was dependent on the annealing time and temperature. High angle x-ray diffraction (HXRD) was used to reveal the overall film structure and growth texture and low angle XRD (LXRD) was used to investigate the quality of the multilayer structures. M-H hysteresis loops revealed in-plane uniaxial anisotropy in as-deposited films which is eventually eliminated with annealing. The easy axis squareness experiences a pronounced decrease with lower temperature annealing, but then increases slightly with annealing temperature.

Giant magnetoresistance with low saturation fields (Hs’s) is reported in Au and permalloy (Ni0.82Fe0.18) or Co-doped permalloy multilayer thin films as-deposited on Ta-overcoated Si and glass substrates. A ΔR/R as high as 4.0% with ≈25 Oe Hs was observed at 295 K for the film consisting of 10 layers of 24 Å Au/13 Å Ni0.82Fe0.18 deposited on a 3 Å Ta-overcoated glass at 50 °C. A Hs value as low as ≈20 Oe with a 15% smaller ΔR/R has been observed for the films with a thicker (e.g., 50 Å) Ta underlayer. Magnetic hysteresis loops of these films indicate the presence of antiferromagnetic exchange coupling between the Ni0.82Fe0.18 layers. This exchange coupling is much smaller for the multilayer films without the Ta underlayer, resulting in a 6x smaller ΔR/R and lOx larger Hs observed for these films. Results of x-ray diffraction analysis indicate stronger (111) texturing for the multilayer films with a Ta underlayer, consistent with the stronger antiferromagnetic coupling between the the Ni0.82Fe0.18 layers in the film. The addition of 2–10 % Co moderately increases the ΔR/R value, but also increases substantially the Hs (up to ≈200 Oe).

The giant magnetoresistance in FeMn exchange-biased NiFe-based multilayer spin-valve structures prepared by rf-diode sputtering technique were studied. Experiments were performed on samples with different thicknesses of each layer in these multilayers. The magnetic properties were measured using a vibrating sample magnetometer and the giant magnetoresistance was measured using an in-line four-point magnetoresistance probe. A magnetoresistance of 6.5% in a magnetic field of less than 15 Oe was obtained in a Cu(30Å)/FeMn(150Å)/NiFe(50Å)/Co(15Å)/ Cu(20Å)/Co(15Å)/NiFe(60Å) multilayer structure at room temperature. Annealing experiments of these multilayers were performed to study the thermal stability during the recording head fabrication processes. No degradation in the magnetoresistance has been found for annealing these films at 230°C up to four hours.

We have investigated the structural properties of Ni80Fe20 thin films sputtered on silicon with Cr, Ta and SiO2 buffer layers using transmission electron microscopy. We observe a decrease of the grain size when Ta and SiO2 underlayers are used instead of Cr. Permalloy films deposited on Ta layers are strongly (111) textured while those grown on Cr and SiO2 are mostly randomly oriented. The results are discussed with respect to the nanostructure of both Ta, Cr and SiO2 underlayers and in relation to the variation of the magnetic softness observed in this system.

Structural defects like local ferromagnetic short-circuits are responsible for large reductions of the intrinsic interlayer coupling in the case of antiferromagnetically (AF) coupled multilayers (ML). We have investigated the role of such point defects in AF-coupled Cu-Co ML’s with tCu=8Å and tCo=12Å which have been irradiated with various doses of 200 keV xenon ions. A significant decrease of the giant magnetoresistance and of the saturation field is observed when the density of defects is increased. These results are compared with a micromagnetic model that takes into account local discontinuities of the AF coupling in an ideally AF-coupled ML. Evidence for the presence of such defects is investigated by TEM on cross-sectional specimens.