钡铁氧体垂直磁化膜磁各向异性研究

钡铁氧体垂直磁化膜可用作高密度磁记录介质。本文研究用低温ＲＦ磁控溅射法制备非晶薄膜，经晶化处理所得到的垂直磁化膜的饱和磁化强度Ｍｓ、矫顽力Ｈｃ及垂直磁各向异性常数Ｋｕｌ、Ｋｕ２与退火温度Ｔ的关系，并对所呈现出的变化规律作了简单解释。介绍了依据转矩曲线的形状来判断薄膜垂直性优劣的方法，从转矩曲线出发，探讨了影响薄膜磁各向异性的因素。     

High coercive force films of cobalt-nickel with additions of group VA and VIB elements

This paper describes some of the structure-property relations for Co and CoNi films containing Group VIB additions, i.e., chromium, molybdenum, and tungsten and Group VA additions, i.e., phosphorus, arsenic, antimony, and bismuth. All films were prepared by electrodeposition. The magnetic properties and metallurgical structure of the films with tungsten cover the same range of parameters as produced with the phosphorus films. The quantity of the elements required to achieve the maximum in coercive force increases substantially in the sequence P, As, Sb, and Bi; and in the sequence W, Mo, and Cr. The saturation moment and coercive force both decrease with increase of the concentration of added element required to attain the maximum coercive force. The quantity of the elements required is believed to be related to the ability of the electrolyte to produce a refinement of the grain size of the deposit, and the ability of the element added to segregate to the grain boundaries. The saturation moments of Co with W and P agree with the results expected for solid solutions except at high concentrations. The structure sensitive magnetic properties obtained with CoNiW films are qualitatively interpreted in the same way as for the CoNiP films, i.e., on the basis of a strongly interacting array of fine particles. The alloys containing Cr, Mo, or W possess improved resistance to aging at elevated temperatures and in corrosive environments.     

Effects of different magnetic flux densities on microstructure and magnetic properties of molecular-beam-vapor-deposited nanocrystalline Fe64Ni36 thin films

The nanocrystalline Fe₆₄Ni₃₆ thin films were prepared by molecular-beam-vapor deposition under different magnetic flux densities. The microstructure and magnetic properties of thin films were examined by AFM, TEM, HRTEM and VSM. The results show that with the increase of magnetic flux densities, the changing trend of the average particle size is the same as the coercive force except 6 T. Under 6 T condition, the thin film became the mixture of bcc and fcc phases, which leads to slight increase of the coercive force. In addition, the HRTEM result shows the short-range ordered clusters (embryos) or nucleation rate of thin films increase with increasing magnetic flux densities.     

The preparation and properties of electrodeposited permalloy films on substrates of evaporated permalloy

The technology of production and some of the properties of isotropic magnetic Ni 80%-Fe 20% films are described. These films were obtained by permalloy electrodeposition onto glass substrates previously coated with vacuum-deposited thin films of Ni-Fe alloy. The change in the magnetoresistance of the films as a function of thickness has been investigated and is discussed, taking into account the influence of the film composition. The results are compared with those previously reported for evaporated films. The dependence of coercive force on film thickness is given. An increase in the crystallite size of the electro-deposited films with respect to the vacuum-deposited substrate has been found.     

Effect of chemical treatment on the magnetic properties of thin-film ferromagnetic systems

The effect of chemical treatments on the surface morphology and local magnetic characteristics of thin films of a FeN alloy and thin-film structures comprising submicron layers of this alloy separated by a silicon dioxide interlayer has been studied by microscopic and magnetooptical techniques. It is established that chemical etching in the presence of a magnetic field strongly changes both the surface morphology and magnetic properties of samples. The local values of the saturation field and coercive force in thin-film structures upon the chemical treatment are significantly different, which is related to the appearance of inhomogeneities on the sample surface and the resulting increased influence of stray fields on the measured magnetic characteristics.     

Thermomagnetic writing in Gd-Co sputtered films

A model for thermomagnetic writing in Gd-Co sputtered films at its compensation temperature is described. In the vicinity of the compensation temperature, the films have rectangular hysteresis loops with large values of coercive force. Spots are thermomagnetically written and erased by using a He-Ne laser in conjunction with an external magnetic field, and a diameter approximately of1.5 sim 2 mum is achieved. Photographs of spots written thermomagnetically are shown. The written domains are circular and clear in shape, and are stable. Temperature dependences of coercive force in Gd-Co sputtered films, and characters of spot diameter as a function of applied magnetic field and writing laser power are reported.     

Some observations on thin magnetic films made by continuously monitoring the coercive force

Conclusions The experimental method described permits the coercive force/thickness relationship to be reliably determined, and avoids the problems encountered by previous techniques. The experimental values of the critical thicknesses, t ₃ and t ₄, at which coercive force anomalies occur, allow the determination of the exchange constant for the magnetic material. Coercive force monitoring during deposition enables films to be prepared with the desired magnetic parameters for computer storage systems. The method is also a useful tool for determining the critical thickness of an intermediate, non-magnetic layer separating two ferromagnetic thin films.     

Structures and magnetic properties of Co and CoFe films prepared by magnetron sputtering

Structures and magnetic properties of Co and CoFe films on Si(100) have been investigated by employing scanning tunneling microscopy, atomic force microscopy, and magneto-optic Kerr effect techniques. As the film thickness increases, Co or CoFe clusters with different sizes are observed. As the film thickness increases below 20 nm, the size of the metal clusters decreases. For thicker films, the surface roughness increases monotonously by increasing the thickness. The easy axis of magnetization for both Co/Si(100) and CoFe/Si(100) prefers to be in the surface plane. By deposition of the Co or CoFe overlayers, the evolution of the longitudinal coercive force shows similar trend to the surface roughness. Minimum coercive force coincides with the smallest roughness of the film. For a film with greater roughness, the observation of larger coercive force could be explained by the impediment of the propagation of domain wall motion by defects of the films. At a higher deposition rate, Co islands in triangle shapes with an edge length around 100 nm are observed. This nanostructure shows an hcp-Co with the c axis parallel to the surface plane and is observed to be able to stabilize the coercive force for Co/Si(100) films.     

Crystal structure and magnetic properties of Permalloy filmssputtered by mixed Ar-N2 gases

The crystallographic and magnetic properties of 1-μm-thick Permalloy films sputtered by mixed argon and nitrogen gases have been investigated. These films are composed of (111) textured grains of face-centered cubic and (002) textured grains of body-centered tetragonal which are deformed from face-centered cubic. Adding nitrogen to argon gas increases the amount of (002) textured grains and lattice strain. The anisotropy field of these films is smaller than that of films sputtered by pure argon. The coercive force of films containing relatively large amounts of nitrogen increases with annealing. The coercive force of the annealed films is correlated with a change in the lattice constant of the face-centered cubic grains. The magnetocrystalline anisotropy of these grains is likely to be one of the causes of perpendicular anisotropy     

The effect of initial growth layer on magnetic properties of Co-Crfilms

The effect of a Ti underlayer, which increases the perpendicular coercive force of Co-Cr films, was investigated. To clarify the cause of this phenomenon, the film-thickness dependence of the magnetic properties was examined. It was found that the coercive force of a Co-Cr film deposited directly on a polymide substrate decreases drastically when it becomes thinner than 50 nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when the film becomes as thin as 20 nm. The film with the underlayer has a distinct uniform columnar structure, whereas the film without it has a 50-nm-thick initial growth layer with no clear structure. Measurements of the temperature dependence of magnetic properties and observations of segregated microstructures indicate that the improvement of magnetic properties by the insertion of the Ti underlayer is mainly due to the improvement of shape anisotropy resulting from the formation of a distinctly segregated microstructure     

Electron microscopy on high-coercive-force Co-Cr composite films

Electron microscopy was used to analyze the crystallographic and magnetic structures of high-coercive-force Co-Cr composite films. The chromium sublayer appears to give high coercive forces by causing the growth of cobalt in the hexagonal phase with a relatively narrow distribution of grain sizes. Magnetization reversal was examined by Lorentz microscopy of films with coercive fields up toH_{c} = 900Oe. It proceeds by nucleation and extension of magnetostatically coupled domains. The progressive limitation of these extensions as the coercive force increases illustrates the connection between the magnetostatic coupling, the coercive force, and the squareness of the hysteresis loop. Lorentz microscopy was also used to investigate a recorded transition between NRZ 1 and 0 states and showed a saw-toothed structure, characteristic of a magnetization in the plane of the film.     

Magnetic properties and longitudinal recording performance of corrosion-resistant alloy films

This paper describes the magnetic properties, recording performance and corrosion resistance of sputtered CoCr alloy films and CoCrTa alloy films. The saturation magnetization of CoCr was 525 emu/cc and not affected by substitution of a small amount of Ta. CoCrTa films exhibit greater coercive force values than CoCr films. The maximum coercive force of CoCrTa was 1400 Oe at a thickness of 400A, whereas at a similar thickness the coercive force of CoCr was 900 Oe. The coercive force decreases linearly with temperature (25°C. to 125°C.) at a rate of 3.16 Oe/°C. for CoCrTa and 1.87 Oe/°C. for CoCr. Longitudinal recording performance at -3 dB signal level was 8386 flux reversals/cm (21,300 fci) and 11,063 flux reversals/cm (28,100 fci) for CoCr and CoCrTa respectively. The alloys exhibited corrosion resistance at 80% relative humidity and 65° C. for a two-week period equivalent to at least six years under ambient disc drive conditions.     

On styrene–butadiene–styrene–barium ferrite nanocomposites

Magnetic investigations on a nanocomposite material obtained by spinning solutions of styrene–butadiene–styrene block copolymer containing barium ferrite nanoparticles onto Si wafers are reported. The effect of the spinning frequency on the magnetic features is discussed. It is observed that the magnetization at saturation is decreased as the spinning frequency is increased as the centrifuge force removes the magnetic nanoparticles from the solution. This is supported by the derivative of the hysteresis loops, which show two components, one with a high coercive field and another with a small coercive field. Increasing the spinning frequency increases the weight of the low coercive field component. The anisotropy in the distribution of magnetic nanoparticles, triggered eventually by the self-assembly capabilities of the matrix, is revealed by the difference between the coercive field in parallel and perpendicular configuration. It is noticed that increasing the spinning frequency enhances this difference. The effect of annealing the nanocomposite films is discussed.     

Simultaneous substitution of Co2+and Zn2+ions in submicronic acicular γ - Fe2O3particles

In iron sesquioxide of acicular shaded γ-Fe2O3simultaneous substitution of Co²⁺and Zn²⁺ions leads to the formation of mixed-defect ferrites and modulation of magnetic properties is of interest for their application to high density magnetic recording. It is shown that the coercive force, remanent magnetization and saturation-magnetization are controlled by a judicious choice of the contents of Co²⁺and Zn²⁺, while it is indispensable to optimize the morphological features like the average size of the crystallites, the shape, the size and texture of the particles. A high value of coercive force (650-700 Oe) and of the remanent magnetization (35-45 emu/g) had been obtained with a minimal content of cobalt ions (Co²⁺= 2.5 to 3% by wt.) permitting limits to the magnetocrystalline anisotropy of these compounds and their thermal variation near the ambient temperature. The influence of the zinc content had been systematically studied notably in relation to its effect on the structural, morphological and magnetic properties of the ferrites.     

Effects of High Magnetic Field on the Structure and Magnetic Properties of Molecular Beam Vapor Deposited Fe₆₀Ni₄₀ Thin Films

The Fe₆₀Ni₄₀ (in atomic %) polycrystalline thin films with 90 nm thickness were prepared on 200 °C quartz substrate by using molecular beam vapor deposition method. The influence of 0 T and 6 T magnetic fields on the structural evolution and magnetic properties of thin films was studied by using EDXS, XRD, AFM and VSM. In this study, only α phase was formed in both thin films. It was found that the application of a 6 T magnetic field obviously decreases the RMS of surface roughness and the grain size. For the magnetic properties of the thin films, the 6 T magnetic field increases the saturation magnetism Ms in-plane and the squareness (Mr/Ms) of the hysteresis loop and decreases the coercive force Hc. This indicates the soft magnetic properties of the thin films have been notably enhanced in-plane by a high magnetic field. The relationship between the structural evolution and magnetic properties was discussed in details.     

Nonlinear domain-wall velocity and coercive force in permalloy films

Domain wall velocities are measured for 2700 Å and 2200 Å thick Permalloy films of several coercive forces. The velocity-drive field curves are characterized by two mobilities, as often reported. It is found that these low- and high-field mobilities are strongly affected by coercive force of the films. The low-field mobility is nearly constant for low-coercive-force films, and decreases rapidly with increasing coercive force. The high-field mobility is inversely proportional to the coercive force. The measured results suggest that the nonlinear dependence of wall velocity on drive field would disappear in a zero-coercive-force film. None of the mechanisms proposed up to now can explain this behavior of wall velocity in Permalloy films. The nonlinearity is attributed to the transition of material inhomogeneities from pinning centers in low field to dissipation centers in high field.     

Domain wall velocity and interrupted pulse experiments

The velocity of magnetic domain walls in Bloch wall Permalloy thin films excited by interrupted easy axis drive fields is investigated and correlated with the available theory of transient wall contraction. The experimental technique is useful in determining the average wall velocity, and by comparing the velocity-field curves with field duration as a parameter it is possible to infer several features of the transient behavior. It is found that, when the displacement of the wall is of the order of a characteristic distance associated with the wall coercive force interaction, the threshold field for net motion as well as the mobility of the average velocity curves depend on the field duration. The theory together with a breakable-spring model of the coercive force interaction reasonably explain the observed phenomena.     

Magnetic properties of sputtered Co-Ni-Fe-Pd films for thin-filmheads

Magnetic properties of Co-Ni-Fe-M (M=Rh, Ir, Pd, Pt) films prepared by sputtering are investigated. It is found that addition of Pd decreases the magnetostriction constant of the films from 1×10^-5 to around zero. On the other hand, addition of other elements, such as Rh, Ir, and Pt, increases it. However, coercive forces of Co-Ni-Fe-Pd films become more than 10 Oe when the magnetostriction is less than 2×10^-6. Multilayered films are investigated to obtain films with low coercive force. 43Co-27Ni-15Fe-15Pd films of 0.17 μm and Al₂O₃ films of 0.01 μm in thickness are layered time-sequentially. This multilayered film has saturation induction of 1.4 T, ≈0 magnetostriction, and a low coercive force of 1.5 Oe. Furthermore, Co-Ni-Fe-Pd films are ascertained to be as resistant to corrosion as Permalloy films. Recording heads with multilayered Co-Ni-Fe-Pd films with Al₂O₃ interlayers as magnetic cores have been fabricated. Recording characteristics were evaluated. These laminated Co-Ni-Fe-Pd/Al₂O₃ heads exhibit about 6 dB better overwrite than Permalloy heads     

Influence of coercive force on low-frequency creep in bloch-wall permalloy films

A very high resolution Bitter pattern technique is used to observe the motion of Bloch walls in Permalloy films excited by slowly rising and slowly falling hard-axis fields. For low coercive force films, the basic motion consists of approximately equal and opposite jumps induced by simultaneous wall structure changes at two transition fields. Net motion begins with the application of small easy-axis bias fields. For high coercive force films, although the wall structure changes continue to occur, the wall jumps and a net displacement do net occur until the easy-axis bias field exceeds a certain critical value which is a function of the wall coercive force.     

Growth of magnetic eutectic GaSb-MnSb films by pulsed laser deposition

Eutectic GaSb + MnSb films ranging in thickness from 80 to 130 nm have been grown on sapphire substrates by pulsed laser deposition using mechanical droplet separation. The films were similar in composition to the ablation target, consisting of the eutectic GaSb-MnSb alloy. According to atomic force and electron microscopy data, the films were homogeneous, with p-type conductivity. Their electrical properties depended significantly on deposition conditions. The best films had a resistivity of 7 × 10^?3 Ω cm, carrier concentration of 8.1 × 10¹⁹ cm^?3, and carrier mobility of 10² cm²/(V s). Characteristically, the films had a negative magnetoresistance. Their magnetization curves showed saturation in a magnetic field of ～1 × 10^?1 T. According to the magnetic-field dependences, the coercive force in the films was within 3 × 10^?2 T; that is, the films were soft magnets with a small domain size.