FePt-Ag nanocomposite thin films with longitudinal magnetic anisotropy

A well-controlled method to fabricate FePt thin films with the (200) texture and longitudinal magnetic anisotropy for high-density magnetic recording media is reported. FePt-Ag nanocomposite thin films with L1(0) ordered FePt grains embedded in an Ag matrix were deposited on the Cr90Ru10/glass by co-sputtering from Ag and FePt targets. The Ag doping suppressed the (001) texture but improved the L1(0) FePt (200) texture. The magnetic easy axis of FePt-Ag thin films changed from perpendicular to longitudinal in direction. In-plane coercivity of the films varied from 0.8 kOe to 6.5 kOe, depending on Ag contents in the films and under-layer thickness. The change from the (001) to (200) texture could be due to the competition of grain-boundary energy and epitaxial-strain energy.     

Frequency response of a thin cobalt film magnetooptic sensor

The magnetooptic effect is due to a change in the polarization of the light when it is reflected or passes through a magnetized material. The rotation of the polarization plane is proportional to the magnetic field. The great advantage of using a magnetooptic sensor to measure intensity or magnetic fields is its wide bandwidth. This fact is widely known; however, no effective measurements have been taken. In this paper, we present the frequency response of a cobalt thin film used as magnetooptic material. It was first excited by several sinusoidal magnetic fields at different frequencies. The range of frequencies studied in the first experiment reached 179 Hz, which is suitable for measuring power line intensity or magnetic fields. Because the coil that creates the magnetic field has a great impedance at higher frequencies, an alternative method based on magnetic impulses has been designed to obtain high-frequency data. With the latest experiments we have been able to measure frequencies as high as 2 MHz, obtaining a flat frequency response.     

Transverse recording using thin film recording heads

This paper presents the results of an investigation of a high density magnetic recording technique utilizing a thin film recording head and a transverse mode of recording on thin media. The significant results of this investigation are as follows. 1) Densities as high as 18 500 transitions per inch were experimentally written in a 300-Å thick FeCr medium having an Hcof 70 oersteds. 2) These densities were written with a thin film, vapor-deposited, recording head having a MATED-FILM® structure with a 0.4-mil etched gap. 3) Track widths of 1-mil on 2-mil centers were experimentally achieved. 4) Optical readout of a 0.2-mil wide transition (width of beam) region corresponding to 5000 transitions per inch was achieved using a laser beam and a linear motion transport system under ideal experimental conditions. 5) The magnetic field from the Néel wall separating recording domains was detected using a MATED-FILM Etched Gap head making this a possible readout method. Maximum achieved linear bit densities as a function of recording media coercivities are given.     

Planar silicon heads/conventional thin film heads - recordingbehavior comparisons

The lower inductance of Planar Silicon Heads (PSH), the output with no undershoot, the low induced noise due to the common mode coil and the P1 equal to P2 with high accuracy make PSH under the same recording conditions of superior performance compared to Thin Film Heads (TFH). In PSH, the uniaxial permeability is parallel to the disc, in contrast to TFH where the high permeability is perpendicular to the disc. This magnetic difference can explain why PSH exhibit smaller PW50. These points will be discussed in this paper     

Recent development of thin film materials for magnetic heads

Recent developments of soft magnetic film materials in the past decade are reviewed. Approximately 20 kinds of alloy systems with high saturation induction of more than 10 kG have been reported in the last decade, although there were only three conventional head materials: Mn-Zn ferrite, Permalloy, and Sendust. A particular focus of the review is nanocrystalline films and multilayer films. Also reviewed are improvements in single-layer homogeneous films of Fe, Fe-Si, Sendust, and Fe/sub 16/N/sub 2/. Almost all the materials reported are Fe-based alloys, and some alloys are nitrogen related: iron-nitride compounds or nitrogen-containing alpha -Fe or Sendust.<>     

High frequency dynamic imaging of domains in thin film heads

A wide-field magnetooptic domain observation system with a time resolution of 10 ns has been developed to study magnetization dynamics in thin-film heads. The instantaneous dynamic response on the top yoke of thin-film recording heads is examined at any chosen instant within the drive current cycle at frequencies up to 20 MHz. Different phase responses from different domain walls in the head are observed and interpreted in terms of hysteretic wall motion, effective field density variation in the head, and wall orientations relative to the flux conduction direction. Two different flux conduction mechanisms associated with two different domain structures in the central region of the head are observed and discussed. Flux conduction in the center of the head by motion of backgap walls and magnetization rotation for domain structures with and without the backgap walls was observed. The domain structure with the backgap walls is probably undesirable because the backgap wall motion may cause a decrease in head efficiency during high-frequency operation and could cause noise during read-back     

Magnetisation distributions in thin film recording heads by Type IIcontrast

The magnetic domain structure of the polepieces of thin-film magnetic recording heads and its variation with drive current and frequency are of interest in understanding the read/write properties of the head. The authors describe the setting up of the synchronous detection mode of type II backscattered electron contrast in a 200-kV electron microscope and its application to the study of domain wall movement in the P2 polepieces of heads with and without the 15-20-μm-thick alumina overlayer in place. Extension of the method to allow evaluation of the changes in magnetization directions under AC drive conditions is described. The authors also demonstrate a novel technique which gives information on the remanent state of the domain structure in the P2 polepiece and its changes under DC drive conditions. It is concluded that these improvements in technique, taken together with the capability of the synchronous detection method to provide information on changes of magnetic structure with depth, mean that this experimental tool will be invaluable in its own right as well as complementary to the Kerr imaging methods     

Elastic anisotropy effect on indentation-induced thin film interfacial delamination

Effect of elastic anisotropy on indentation-induced thin film interfacial delamination, especially, at the initiation and early growth stage, is examined. The indentation load is modeled as a constant pressure over an expanding semi-spherical cavity. The delamination process is approached by a cohesive zone model. The rest of the problem is formulated within the general anisotropic elasticity theory, and solved numerically by the boundary element method employing a special Green’s function for multilayers. The material system of a Cu(0 0 1) film on a Si(0 0 1) substrate is studied as an example. The interfacial damage initiation and crack development under indentation are captured in the simulation. By comparing the predictions with the materials being modeled as isotropic and as anisotropic (of the cubic symmetry as they are), it is shown that the elastic anisotropy of the copper film plays a significant role in determining the delamination pattern. In the isotropic model, the delamination crack fronts are circular reflecting the problem axisymmetry. In contrast, crack fronts are square with rounded corners in the anisotropic case. This significant difference necessitates a three-dimensional anisotropic stress analysis of the indentation-induced delamination of strongly anisotropic films.     

Recording on perpendicular anisotropy media with ring heads

This paper reports experimental studies directed at the application of ring head structures to a perpendicular recording system. The media tested were sputter deposited films of CoCrTa alloys. Ferrite heads were studied, but the thin film head was chosen for evaluating roll-off, overwrite, and superposition. The data presented in the paper demonstrates the potential of high density recording with a single layer medium with perpendicular magnetic anistropy and a thin film head separated by 0.20 micrometers.     

Magnetic anisotropy of thin metallic film tapes deposited at oblique incidence

The origin of magnetic anisotropy of thin films deposited at oblique incidence is investigated. Electron micrographs of such films prepared at various incident angles demonstrate a characteristic particle structure. A model of the film developed on this basis is composed of identical elongated rotation ellipsoids whose long axes are oriented parallel to the beam direction. The energy densityFis calculated for all orientations of magnetization, taking into account the shape anisotropy of the particles and the interaction of their stray fields. Hence the anisotropic properties of the film are obtained. The comparison of calculated and experimental results verifies the assumption that anisotropy is caused preferably by effects of shape induced by technological processes. The parameters of films with optimal storage properties (maximum energy product) can be determined theoretically by the suggested method.     

Demagnetization-free longitudinal recording on flexible thin film metal media

The variation of demagnetization effects with media parameters for longitudinal contact recording has been investigated. Co-Re thin film metal media were sputtered onto flexible polyimide substrates. It was found that when the film thickness δ and demagnetizaton parameterB_{r}delta/H_{c}were less than 2 μ inch and 15 μinch, respectively, demagnetization-free longitudinal recording was obtained up to the recording density of 75 KFRPI at the head-to-medium spacing of 3 μ inch. As a result, recording densities of D50over 50 KFRPI were achieved with a 20 μinch gap head. For thicker films with larger demagnetization parameters, i.e.,delta geq 4 muinch andB_{r}delta/H_{c} geq 40 muinch, the longitudinal recording process approached the demagnetization limit. The results show that (with existing head field gradients) improvement in linear density of thin metal media can be obtained by an approximate factor of two before the demagnetization limit is reached.     

Toward an understanding of grain-to-grain anisotropy field variation in thin film media

Grain-to-grain anisotropy field variation has become one of the main causes of medium noise, especially in perpendicular thin film media. In this paper, we present an electron microscopy investigation and theoretical analysis on the grain-to-grain anisotropy field variation in various types of thin film recording media. In alloyed film media, the intrinsic grain-to-grain composition variation would present a lower limit on grain size, thereby limiting area recording density. It is also argued that partial ordering in L1/sub 0/ materials such as FePt would yield large anisotropy field variation, especially for low values of order parameter.     

Batch fabrication of thin film magnetic recording heads: A literature review and process description for vertical single turn heads

Several publications in the past have discussed the potential of batch fabricated thin film heads. Most of these publications dealt with theoretical predictions. Only a few discussed fabrication techniques and reported on the write and read test results. This paper describes a fabrication process for single turn thin film heads of vertical configuration. The process utilizes well known evaporation, plating, and photolithographic techniques. It is simple, inexpensive, and amenable to batch fabrication. Heads fabricated using this process were shown to write and read on a disk, moving at 40 m/s (1575 in/s) with ∼6 Kfr/cm. Dynamic test results reported in a paper by Valstyn and Shew corroborate the earlier prediction. This paper also discusses and compares advantages and disadvantages of the single turn heads of a vertical configuration with those of a horizontal configuration.     

Effects of elastic anisotropy on the surface stability of thin film/substrate system

The surface stability of thin film/substrate system is an important problem both in the film synthesis and reliability of micro electrical and mechanical system (MEMS). In this work, the elastic anisotropy effect on surface stability of thin film/substrate system was considered. The theoretical analysis indicates that elastic anisotropic influence could play an important role in the surface stability of thin film/substrate system. And the anisotropy effect should be considered both in the thin film synthesis process and its service reliability. In addition, there exists an nondimensional parameter k for cubic crystalline thin film materials in evaluating the anisotropic effect. When k is larger than one unit, the surface stability will be weakened by anisotropic effect; vice versa. The method used in present work could be easy extended to multi-layered thin film/substrate system and help us to consider the elastic anisotropy effect.     

Perpendicular magnetic recording with a composite anisotropy film

For a recently proposed perpendicular recording system, a composite anisotropy medium has been developed to improve the recording sensitivity of the perpendicular recording head. The medium is composed of a Fe-Ni soft magnetic film and a Co-Cr perpendicular anisotropy film, which are successively deposited on a base by an r. f. sputtering. By using the new double layer medium, an extremely high recording sensitivity could be obtained, compared with the single layer Co-Cr medium. The recording current needed to saturate the double layer film decreased to one-tenth of that for the single layer Co-Cr film. Although the Fe-Ni layer was soft magnetic material, neither deterioration of the frequency response nor peak shift was observed for the double layer film. The reproduction with a perpendicular head was also investigated, and a high output voltage and a high signal-to-noise ratio were obtained.     

Domain splitting in thin films with in-plane anisotropy

Splitting of magnetic ripple into domains due to an external magnetic field was observed using the defocused electron microscopy method. The tested film was magnetized perpendicularly or parallel to the easy axis of the uniaxial anisotropy, and both the magnetic field direction and the anisotropy axis lay in the film plane. Splitting of the ripple into 1 μm domains was mainly reversible until the value of ripple amplitude reached 0.5 rad. Movements of the Néel walls and Néel-Bloch-Néel transformation of the domain walls were the main irreversible phenomena which led to hysteresis. Domain splitting of the ripple is properly described only by a Riedel model which includes the interactions between cores and tails of the periodically arranged Néel walls.