This paper is concerned with the experimental results of the high rate and low temperature deposition of Co-Cr films using an exposed pole (EP) magnetron co-sputtering system developed by the authors for deposition of ferromagnetic binary alloy films. In this paper we prepare a composite target constructed of a Co washer, a Cr cylinder and a Co disk, and examine the performance of the sputtering system and evaluate the film quality.
Results :
1) Maximum deposition rate was as high as 0.18 μm/min for 7.6 W/cm² input power.
2) The deposition rate was higher for lower sputtered gas pressure.
3) The substrate temperature was as low as 100°C for 7.6 W/cm² input power.
4) The C-axis of the deposited Co-Cr films were in the perpendicular direction to the film plane and Δθ₅₀=8-13°.
5) Perpendicular magnetic anisotropy films were obtained for the films of M_s=300-800 emu/cc and H_c=250-350 Oe.
Thus, it is concluded that EP magnetron co-sputtering is very effective for the deposition of Co-Cr films.

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CoCr thin films having a thickness from 0.014 μm to 0.5 μm were prepared by D.C. magnetron sputtering method using CoCr (18 wt% Cr) alloy target on PET film.
Thicker films are characterized on three zones which have different magnetic properties. In the first zone, films up to 0.03 μm thickness have very low coercive force H_c and small saturation magnetization M_s, and a poor vertical anisotropy. In the second zone from about 0.03 μm to 0.1 μm, H_c and M_s vary passing along the maximum value, but in this zone anisotropy field H_k is smaller than that of the third zone. In the third zone H_c gradually decreases with increasing film thickness, while M_s approaches a constant value and M_s reaches the highest constant value. TEM studies show CoCr films to have a fine columnar structure in thickness greater than 0.03 μm, and no changes in structure or diameter of the column have been observed in the 2 nd and 3 rd zones.
To investigate the effects of the underlayer, various kinds of metal were deposited on the PET film prior to CoCr deposition. Double layered CoCr films exhibit higher H_c than single layer and have poor crystalline orientation. SEM observation shows that CoCr films on the metallic underlayer have smaller grain size than do single layered films.

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The effects of H₂, O₂ and N₂ additives on the magnetic properties of Co-Cr film were studied for high rate sputtering. O₂ and N₂ react with Co-Cr to from compounds. N₂ addition induces fcc <200> orientation perpendicular to the film plane, and hence causes a drastic decrease of the perpendicular anisotropy field H_k, accompanied by hcp <002> orientation degradation. O₂ is most reactive to Co-Cr, but little affects the crystal structure. These effects become less at higher deposition rate for the same introduced pressure. In contrast, H₂ does not react with Co-Cr at all, but has a unique role of changing the coercive force without any change of H_k or crystal orientation. The effects of N₂ and H₂ are concluded respectively equivalent to that of increase and decrease of substrate temperature.

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In order to investigate the reversal mechanism of magnetization, angular dependence of hysteresis loss was discussed for Co-Cr perpendicular recording media. For a so-called double layer medium which consists of a Co-Cr layer and a Permalloy back layer, it was easily shown that the Co-Cr layer shows rotational reversal of magnetization. Judging from both angular dependences of H_c and hysteresis loss, the initial and column layers in Co-Cr sputtered film were found to show magnetization reversal by domain wall motion and by rotation, respectively. Other Co-Cr films which have different M_s and H_c were also studied with respect to their reversal mechanism of magnetization.

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Perpendicular magnetic recording is promising for the achievement of higher recording density. Magnetic and crystal orientational properties of double layer rigid disks for perpendicular magnetic recording were studied. Coercive force distribution of the Mo-Cu-permalloy underlayer was investigated as a function of sputtering gas pressure. At optimum Ar gas pressure, good uniformity of coercive force distribution was obtained. Even in double layer medium, crystal orientation of the Co-Cr layer was influenced by the characteristics and thickness of the substrate surface treatment layer. Higher recording density was obtained with lower flying height and a thinner Co-Cr layer. The D₅₀ recording density of 70kFRPI was achieved for a 0.15 μm thick Co-Cr layer and a 0.3 μm thick single pole type head at 0.1 μm flying height.

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To clarify the influence of CoO spins on magnetic properties of Co-CoO reactive sputtered films, Co-CoOx compositionally modulated (C.M.) films were investigated. These Co-CoOx C.M. films were prepared with modulating oxygen partial pressure in a chamber (Po₂). These films have Co-CoO interfaces parallel to the film plane. Coercivity (H_c) and in-plane anisotropy (K_//) of C.M. films with short modulating periods increase remarkably below Néel temperature of CoO (=292K). These increases in H_c and K_// at low temperature are thought to originate from the magnetic interaction between Co spins and CoO spins.

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Electroless Co alloy films tor perpendicular magnetic recording medium were investigated as a function of thickness dependence on magnetic properties. The read/write characteristics, especially the dependence of overwrite on recording density showed a large difference between Co-Ni-Re-Mn-P and Co-Ni-Re-P films. Since those films displayed a different thickness dependence of perpendicular coercivity H_c(⊥) , the control of thickness dependence of H_c(⊥) was attempted for Co-Ni-Re-P alloy films. The thickness dependence of H_c(⊥) of Co-Ni-Re-P alloy films could be easily controlled by adjusting the sodium malonate concentration in the bath. When the film becomes very thin, such as 0.1 μm thick, the H_c(⊥) value and degree of c-axis orientation increased with an increase in sodium malonate concentration, however, when the film thickness increases up to 0.5 μm. those values become almost the same for different sodium malonate concentrations.

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Stress and temperature stabilities for Ba-ferrite perpendicular magnetic recording media have been investigated. Stress-induced decrease rate in remanent magnetization for the media was found as small (1 × 10^-5 per kg/cm²) as those for metal and Co-γFe₂O₃ media. Remanent magnetization in a perpendicular direction remains almost constant in a −10 to 80°C temperature range. Output decreases after 120 minutes still mode reproducing with 8 mm VCR, and 10 million passes with a 3.5 inch FDD were less than 1 dB. These results confirm the excellent stability of the Ba-ferrite recording media.

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Magnetic thin films of Mn-ferrite (MnFe₂O₄) have shown a large perpendicular magnetic anisotropy by the evaporation method. The evaporation substances are the (A_αB_β)_100-xC_x system, where A, B and C represent the matrix elements of combination for Mn, Fe and Bi, respectively. For (Mn₂₅Fe₇₅)₉₇Bi₃ the pillar-shaped grain, MnFe₂O₄ deposited onto substrate has an anisotropy constant of 4.4 × 10⁵ erg/cm³, 4_πM_s 1.6 × 10³ gauss and H_s 540 Oe. The configuration and magnetic properties in evaporated film composition are closely related. It was recognized that in order to get magnetic thin films with perpendicular anisotropy it is important to form a first layer of Bi phase with <102> configuration onto substrates.

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An observation method where the primary electron beam is parallel to a sample is proposed. The leakage magnetic field emanating from recorded magnetization is observed in the secondary electron image by a scanning electron microscope. The secondary electron image is generated due to the quantity difference of secondary electrons, which depends on whether the electron beam is incident to the sample or not, as a result of the horizontal component of the leakage magnetic field. The secondary electron images for the perpendicular recording and the longitudinal recording are shown. A two micron recording length can be resolved by this method.

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A novel magnetic read-out principle is proposed which can extract a high quality output from a high density recorded signal. The principle utilizes a sharp RF permeability change in a soft magnetic film due to a weak external field. This variation is caused by both magnetization rotation and ferromagnetic resonance.
A magnetic read-out head has been experimentally made which operates according to the novel principle. The manufactured head was evaluated by sinusoidal signals (0.5-10 MHz) which are saturatedly recorded in a magnetic tape with a ferrite ring head (head gap : 0.3 μm, track width : 100 μm).
The reproduced 0.5MHz signal level from the head is at least 35.7dB higher than that from the ring head, and the 5 MHz signal is 17.6-22.5 dB robustly detected by the novel head. The carrier-to-noise ratio for a 5 MHz carrier (1 μm wavelength) is 44-47 dB and is insusceptible to Ni-Fe film thickness.

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Effects of domain structures of main pole films on reproducing sensitivities are investigated for single pole type perpendicular magnetic recording heads. The reproducing sensitivity of the single pole head made of a Co-Zr-Nb single layer becomes unstable and decreases with the increase of the closure domain size when the track width narrows and the anisotropy field H_k decreases. On the contrary, for a narrow track main pole made of Co-Zr-Nb multilayered amorphous film with 50 Å thick SiO₂ interlayer, the closure domain cannot be observed clearly. Consequently, the reproducing sensitivity becomes larger than that of the single layer main pole and the reproduced voltage is very stable even for smaller H_k and narrower track.

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A tilted sendust sputtered (TSS) ferrite head has been developed for use with high coercivity metal tape in high recording density VTR systems. Because the sendust-ferrite boundary plane is at an angle to the gap plane in the TSS head, the interference peaks in the playback output spectrum caused by the pseudo gap between the sendust and ferrite core are significantly reduced. The improved electro-magnetic characteristics of the head produced from sendust-ferrite composite materials have practical application in the field of magnetic recording technology.

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Write spacing losses in perpendicular magnetic recording have been investigated experimentally for a ring head and a single pole head. In ring head recording, an increase of write spacing causes the change of magnetization mode in the Co-Cr layer from perpendicular to longitudinal. In single pole head recording, the magnetization mode remains perpendicular, even for large write spacing. Furthermore, the reproduced voltage in saturation recording decreases with increased write spacing, since the magnetization transition length is broadened by the decreasing write head field gradient resulting from disappearance of head-to-medium magnetic coupling. Therefore, in perpendicular magnetic recording, a slight reduction of the head-to-medium spacing leads to a remarkable improvement in high density recording characteristics.

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Computer simulation of perpendicular magnetic recording has been carried out by applying the modified coherent rotation model (Stoner-Wohlfarth model) to the magnetizing process of a Co-Cr layer. The modification has been made so as to fit the calculated M-H loops in the measured loops for various directions of applied field. Using this model, the M-H loop of a sputtered Co-Cr film can be restored by calculation. The reproduced wave form of an isolated pulse and the bit density response obtained by the simulation using the modified S-W model agree well with measurements.

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The noise properties of magnetic recording media partly depend on the type of media, i.e., magnetic thin film type or particulate type. In magnetic thin film media, such as Co-Ni-P plated disks, the lowest noise level is that of dc-erased noise, and when signals are recorded after dc-erasing the level of the modulation noise increases gradually as the recording wavelength is shortened until it reaches a maximum level at a certain wavelength.
On the other hand, in particulate media, the noise level is highest for modulation noise, followed in turn by dc-erased noise and ac-erased noise.
In the analysis described in this paper, the irregular fluctuations in the direction of magnetization and the number of magnetic particles per unit volume have been taken into account, and the results of the analysis make it clear that the relative noise level of the ac-erased, dc-erased and modulation noise depends on these fluctuations.

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The simulation of the spacing between a magnetic head and medium has been done to investigate the spacing characteristics for the head shape on a video floppy. In this simulation, the finite-element method is used to solve Reynold's equation and the equation of motion for the transformation of medium. Both the equations are discretized simultaneously. The following results were obtained by this analysis: 1) This method efficiently obtains a convergent solution despite the non-linearity of these equations. 2) The spacing has a tendency to be constant for the head protrusion. 3) The effect of the groove on the head surface is the same as that of the narrow track width of the head. 4) For actual use, sufficient depth and width of the groove are more than 2 μm and 5 μm, respectively.

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A new potential well measurement method, using the bubble run-out phenomena, has been discussed for its application to observe charged wall behavior as well as to measure potential well depth itself. The method is applied to bubbles in ion-implanted propagation patterns on 1 μm bubble garnet films with different magnetostriction constants. Bubble run-out directions are found to be reflected by the strength of stress relaxation induced magnetic anistropies along ion-implantation pattern edges. Charged wall length and its stray field distribution are also estimated by the method. It is concluded that this method is one of the most useful tools for operation error mode analysis in ion-implantion bubble device development.

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Computer simulation of the dynamical behaviour of domain walls in bubble films, e.g., for the development of the different functions of the Bloch line memory, are commonly based on the domain wall model developed by Slonczewski. To investigate the degree of reliability of this wall model, we compared numerical results of the dynamics of an infinitely long straight stripe domain with stripe translation measurements, where drive pulses of the order of 2-10 Oe and 50-200 nsec were applied and the total displacement of the stripe, including overshoot, was measured. Numerical and experimental results for the total displacement agree well for drive fields below the experimentally determined breakdown field. The values obtained for the breakdown field also agree well in most cases; however, the discrepancy increases with increasing film thickness and drive field strength. Another discrepancy is the numerical result of a strong dependence of the stripe velocity on the drive field after breakdown in case of thicker films, which is not seen experimentally. Both discrepancies are thought to be results of implicit limitations of the wall model.

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Anisotropy changes caused by He⁺ or H₂⁺ implantations on (100), (110) and (111) magnetic garnet films have been studied. In (100) films, quite in contrast to (111) films, uniaxial anisotropy field changes were almost the same for He⁺ and H₂⁺ implantations. In (110) films, orthorhombic anisotropy parameter B for H₂⁺ implantations changed greatly, which is consistent with anisotropy change for (111) films. The change in parameter A for He⁺ implanted (110) films was in the same order as for H₂⁺ implantations. Magnetocrystalline anisotropy K₁ in H₂⁺ implanted films was determined from the angular dependence of (100) inplane resonance fields. The sign of K₁ changed to positive by H₂⁺ implantations. It was found that H₂⁺ implantations have a great effect λ₁₁₁ and K₁ but have little influence on λ₁₀₀.

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It is found that a large orthorhombic anisotropy is induced in (EuBi)₃Fe₅O₁₂ garnet films grown on (110) NdGG substrates. The Bi content is controlled by controlling the melt composition and the supercooling temperature. Gyorgy's parameter B=−2(K_u+K_p) increases linearly with the Bi content. The main part of B is found to be growth-induced. Gyorgy's parameter A=K_p−K_u is very small and almost independent of the Bi content. The growth- and stress-induced parts of A are found to be considerably large, but of opposite sign, and to compensate each other nearly completely, although their respective absolute values increase with increasing Bi content.
Magnetic properties of a (Eu_1.8 Bi_1.2) Fe₅O₁₂ film are obtained as follows: saturation magnetization 4πM_s = 1560 Gauss, uniaxial anisotropy K_u = 1.6 × 10⁵erg/cm³, in-plane anisotropy K_p = 1.6 × 10⁵erg/cm³, quality factor Q = 1.7, material length l = 0.06 μm and wall mobility μw = γΔ₀/α = 19 ms^-1. Such a film might be used as a 0.5 μm bubble material for current access devices.

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Magnetic moment m, Curie temperature T_c, density ρ and Young's modulus E_S of amorphous Mn-Y, Fe-Y, Co-Y, (Fe-Mn)₈₀Y₂₀ and (Fe-Co)₈₀Y₂₀ alloys fabricated by rapid quenching have been measured to make clear microstructures of amorphous alloys. Detailed comparison of m, T_c, ρ and E_S between amorphous alloys and corresponding crystalline compounds, and a structural analysis by X-ray diffraction reveal a close correlation of an atomic short range order of both states, which is especially found in alloys with Y content less than 30at%. A structural variation between 30 and 40 at%Y in the Fe-Y amorphous alloys is also indicated by the composition dependence of m, T_c, ρ, E_S and by X-ray analysis.

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Amorphous magnetic films have unusually large extraordinary Hall coefficients. We prepared Sm-Co amorphous films with planar or perpendicular magnetization and studied the galvanomagnetic effect in these films. In this paper we report the S_m concentration dependence of electrical resistivity ρ, Hall resistivity ρ_H, Hall sensitivity S and Hall voltage V_{H P-P}. We found that ρ_H is large because of the large saturation magnetization M_s and electrical resistivity ρ. The maximum value of ρ_H is 9.0 μΩ-cm at 15 atm. % Sm. We also studied the magnetoresistance of these films.

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The plastic flow has been investigated for Co-base amorphous alloys with some additive elements, Fe₃Co₇₁Si₈B₁₆M₂ from creep measurement employing a constant heating rate method near the glass transition temperature. The activation energy in the creep process was found to be proportional to the atomic volume of the additive elements which were determined from the Goldschmidt radius. The observed activation energy was changed from 1.92 eV to 2.53 eV in Co (1.25 Å) and Nb (1.47 Å), respectively.
The field induced anisotropy energy K_u hes been measured for the same alloy series. It was found that K_u decreased with the increasing of the atomic volume of the non-magnetic additive elements. In the case of nearly the same atomic volume of the additive elements, K_u seems to depend on the strength of the magnetic interaction. From these results, the degree of the rearrangement of the atoms and the magnetic interaction between magnetic atoms play a dominant role in the field induced magnetic anisotropy.

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Magnetic properties of amorphous magnetostrictive FeCoSiB-alloy wires, made by the inwater quenching technique, were studied. Domain pattern observation on the wire surface was made as a function of alloy composition and of applied magnetic field and tensile stress along the wire axis. The domain pattern was found to disapper at an axial field of 40 Oe and a tensile stress of about 12 kg/mm². The residual stress is estimated to be 4-10 kg/mm². Large Barkhausen and Matteucci voltage pulses and domain nucleation field in Fe_77.5Si_7.5B₁₅ wires were found to decrease to zero at a compressive stress of 5 kg/mm².

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Magnetoelastic waves (MEWs) propagating in a thin conductive magnetostrictive slab were investigated theoretically taking account of the micro-eddy current contribution. The analysis was performed under the assumption that the medium is amorphous (isotropic elasticity) but has a uniaxial magnetic anisotropy in the slab plane. MEWs in this configuration are three fundamental modes: Lamb-type wave of the extensional mode (EMEW), SH-type wave (SMEW) and Lamb-type wave of the flexural mode (FMEW). The microeddy current crucially affected the propagation properties, thereby increasing the propagation loss as well as decreasing the controllable MEW velocity with external magnetic field. The amounts of these quantities also varied depending strongly on the anisotropy orientation β for the above three wave modes, because the degree of coupling between the magnetization and the lattice through magnetoelastic interaction is different in each mode. The present analysis revealed that SMEW with β=45° is the most favorable for delay line application.

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