Co-Cr Layer Research Articles

垂直磁気記録特性の近似解析法

In perpendicular magnetic recording using a single pole type magnetic head and a double-layered medium, a sharp magnetization transition is formed in the Co-Cr layer of the medium because the demagnetizing field rarely arises in the region of magnetization transition. Therefore, the shapes of isolated pulses can be easily calculated by a head field and a M-H loop of the medium. In this paper, a simple mean of approximation for the analysis of an isolated pulse shape in perpendicular magnetic recording is described. For the analysis, the distribution of the head field is computed by FEM considering the head-to-medium magnetic interaction, and an actual M-H loop are used. The calculated narrow pulse width in perpendicular magnetic recording is compared with those measured and calculated in longitudinal magnetic recording.

DECAY OF THE REMANENT MAGNETIZATION IN CoCr FILMS

We have performed measurements of the decay of a signal recorded on single layer CoCr films using a thin film ring head. These results are compared with data obtained by magnetometry of magnetization decays in uniformly saturated samples. The importance of the demagnetizing fields on these measurments is discussed briefly.

Dependence of Recording and Reproducing Characteristics on Thickness of Co-Cr Layer in Perpendicular Recording

Dependence of Recording and Reproducing Characteristics on Thickness of Co-Cr Layer in Perpendicular Recording

Studies on coercivity in Co-Cr thin films by means of a multilayer technique

It is known that there is a significant dependence of perpendicular coercivity Hc⊥ of Co-Cr sputtered thin films on thickness δ even if substrate temperature Tsub is constant during film deposition. Such a δ dependence of Hc⊥ suggests the nonuniformity of magnetic properties normal to the film plane. In order to prepare Co-Cr thin films with satisfactory magnetic homogeneity, multilayered films composed of many Co-Cr thin layers were fabricated by the facing targets sputtering (FTS) system. The experimental results indicated that these multilayered films may be magnetically and crystallographically homogeneous. For example, films deposited at Tsub of 150 °C with thicknesses above 1000 Å have Hc⊥ about 1.5 kOe, however, Hc⊥ of the multilayered films piled up with 300-Å-thick Co-Cr layers which are deposited even at Tsub of 150 °C indicate almost the same value as that of the 300-Å-thick unit layer. Those are about 500 Oe regardless of the total thickness of multilayers. Hc⊥ of the multilayered film depends not only on Tsub but also the thickness of the unit layer.

CoCr double-layered media with NiFe and CoZrNb soft-magnetic layers (invited)

The magnetic, structural, and recording properties of CoCr double-layered media are investigated. The underlayer materials NiFe (crystalline) and CoZrNb (amorphous) were combined with two different kinds of intermediate layers: Ti (crystalline) and Ge (amorphous). Applying a bias voltage during sputtering of NiFe results in a low coercivity of the NiFe layer and in a high coercivity of the CoCr layer. The structure of the NiFe layer influences the structure of the CoCr layer. A Ti layer between the NiFe and CoCr layers decreases the in-plane remanence of the CoCr layer. The coercivity of all CoZrNb layers is low, independent of the application of a bias voltage. The orientation and structure of CoCr on CoZrNb can be improved by using a Ge intermediate layer, which results in a low coercivity of the CoCr. A Ti intermediate layer increases the coercivity. Ring heads show a dependence of spike noise on the underlayer coercivity and on the applied normal force. A probe-type head shows a dependence of its output on the CoCr coercivity, which may be understood in terms of demagnetization and writing depth.

Rf sputtered CoCr for magnetography

In order to improve the resolution in the inking of the dots, vertical anisotropy media configuration is applied to magnetography. The magnetization transition zone length between the dot and the nonmagnetized drum is hoped to be shorter than in the longitudinal configuration. Some preliminary inking tests were successfully carried out on plane samples. A specially designed sputtering group was built for the deposition of CoCr layers. The substrates are full-size drums (diameter=10 cm, length=40 cm) and the Co80Cr20 target is a cylinder (diameter=20 cm, length=50 cm) around the drum. In this paper, the first results obtained with this group are described. The dispersion of the properties of the CoCr layer around the drum is less than 10%. The whole incident power range (up to 15 kW) was scanned. The deposition rate continuously increases with increasing incident power (Pw) up to 9 kW. This rate saturates after 9 kW to a value of 20 Å/s. As in the planar diode sputtering system, the vertical anisotropy of CoCr thin films is improved when high Pw values are used. For these reasons, the optimal incident power was determined as 9 kW. These results show, for the first time, that a dry process could be used for the deposition of a magnetographic medium on a drum.

Structural, magnetic and recording properties of Co-Cr layers for perpendicular recording using Ge nucleation layers

The influence of amorphous Ge underlayers on the structural, magnetic, and recording properties of Co-Cr recording media was studied. The media were prepared by RF sputtering on PET (polyethylene terephthalate) substrates just above room temperature. The Ge underlayer is observed to promote the perpendicular anisotropy of the Co-Cr, provided the Ge-layer thickness exceeds a critical value of about 200 nm to effectively seal the PET substrate. The resulting films also show low coercivity (10 to 30 kA/m), a columnar structure (column width 30 to 50 nm), and signal and noise features as described earlier for media, deposited at low temperature directly on the PET substrate. From the slope of the perpendicular hysteresis loop, the maximum in the noise spectrum, the noise periodicity and erasure experiments the medium domain period is estimated to be 370 to 780 nm for a 600 nm thick Co-Cr layer. These domain periods are consistent with a continuous perpendicular film model of the medium.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Co-evaporation of Co-Cr at intermediate oblique incidence

The coevaporation technique has been used for deposition of Co-Cr layers. Deposition has been done under intermediate angle of incidence of opposing vapor streams. The layers showed a single-phase HCP polycrystalline structure. The

Enhanced perpendicular coercive force of CoCr film formed on a very thin initial sublayer

Perpendicular coercivity of CoCr sputtered films on Ti adhesive layers decreases drastically as RF sputtering power increases. A very thin CoCr sublayer deposited at low power enhances the coercivity of the succeeding CoCr layer. Magnetic properties and segregated microstructures show that the initial segregated microstructure is inherited by the main CoCr layer even though the RF sputtering power changes during the sputtering process. Its segregated microstructure is enhanced by the initial 100-AA segregated structure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ｃｏ‐Ｃｒ膜の結晶配向度の垂直抗磁力に及ぼす影響

Higher vertical coercivity of Co-Cr film is needed in order to obtain highr reproduced output. In this paper, we report how to obtain high vertical coercivity of Co-Cr film using PET film as the substrate. A low degree of crystal orientation in Co-Cr film yields a high vertical coercivity of the Co-Cr film. In double layer media, crystal orientation of Co-Cr layer is changed with that of permalloy underlayer. A high reproduced output was obtained up to 100 kBPI using the Co-Cr/permalloy double layer media with high vertical coercivity in the Co-Cr layer and a single-pole head. The inclination of the easy axis in a simple magnetic wall motion model or a rotation model cannot explain the increase in the vertical coercivity. The degradation of the orientation of the Co-Cr film may increase the Cr segregation in Co-Cr film, and then its vertical coercivity is increased.

High Density Recording with Single Pole Head

The feasibility of high-bit-density recording was investigated experimentally using a perpendicular magnetic recording system employing a single-pole head and a Co-Cr/Ni-Fe double-layer medium. To improve the reproducing sensitivity and resolution, the following were adopted: (a) a newly-developed high-sensitivity single-pole head; (b) a medium with a relatively thin (0.1 μm) Co-Cr layer and a thick (0.5 μm) Ni-Fe underlayer; and (c) a head-medium spacing of less than 0.03 μm. As a result, reproduced signals were detected at up to 680 kFRPI. The recording bit length at the highest density was of the order of the Co-Cr layer columnar grain diameter of the medium. This result proves that recording at densities approaching the intrinsic limit is possible, because the perpendicular recording method is free from recording demagnetization effects at high densities.

垂直磁気記録特性のＣｏＣｒ層厚み依存性 計算機シミュレーションによる検討

垂直磁気記録特性のＣｏＣｒ層厚み依存性 計算機シミュレーションによる検討

High performance heads for perpendicular recording

Several important features of past, present and future developments in the field of heads, specifically designed for perpendicular DL (double-layer) media, are outlined. The emphasis is probe heads (PHs) that are positioned on one side of the medium only. The fabrication and measurement of experimental, high-efficiency PHs, the so-called VSPs, are discussed. The experiments indicate that thin Co-Cr layers with a high coercivity are needed for a good short-wavelength response. This imposes several requirements on the pole material, such as a high saturation magnetization, low Barkhausen noise, and high permeability. A playback model is described that enables the head, medium, and interface parameters to be analyzed. The model has also been used to estimate the bit densities that can be obtained with PHs on DL media. An areal density of 1 bit/ mu m/sup 2/ appears feasible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Possibilities of perpendicular magnetic recording

The potential of perpendicular magnetic recording using a single-pole head and a double-layered medium has been investigated theoretically by computer analysis and compared with that of longitudinal magnetic recording. In conventional longitudinal recording, a recording demagnetizing loss due to the change of magnetization mode from semicircular to circular shapes occurs with increasing recording level at high bit density. In perpendicular magnetic recording, the perpendicular magnetization mode is maintained regardless of recording level even at an extremely high bit density of 571 kFRPI. This indicates that the perpendicular recording medium has a very high recording resolution, where a single bit size approaches several diameters of the microcrystalline particles of the Co-Cr layer. An ultrahigh density at which the recording area for 1 bit will reach 1 mu /sup 2/ at present and 500 AA/sub 2/ in future should be possible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of magnetization distribution in double-layered perpendicular magnetic recording medium

Perpendicular magnetic recording using a single-pole head and a double-layer medium has been simulated with computer to investigate the mechanisms of its extremely high density recording. Self-consistent vectorial magnetization distribution in the interior of a Co-Cr layer have been computed by introducing the curling incoherent model for the magnetization reversal of crystalline particles in the Co-Cr layer. The effect of the head-to-medium magnetic interaction on the head field distribution or the vectorial magnetization transition has been examined by the simulation.

The magnetic anisotropy in the initial layer of Co-Cr sputtered thin films

Co-Cr thin films prepared using Facing Targets Sputtering (FTS) System show well c-axis orientation even at the early stage of the film growth. However, the very thin 200Å-thick film exhibits the large (Mr/Ms) and the in-plane magnetization. This may imply that the critical thickness based on the stripe domain theory is larger than 200Å. In order to investigate the perpendicular magnetic anisotropy in this very thin film, the triple- and multiple-layered films composed of 200-Å-thick Co-Cr layers and non-magnetic carbon spacing layers between them have been prepared. When the thickness of spacing, layers are sufficiently large, the magnetization characteristics of these films are similar to that of 200-Å-thick single layer one. On the other hand, when the spacing layer is as thin as 50Å, the magnetization in the films is perpendicular to the film plane. It has been clarified from the theoretical consideration that the magnetostatic energy of the multilayered films is lower than that of single layer ones. As a result, even the very thin films such as 200-Å-thick prepared by FTS system seems to have the large perpendicular magnetic anisotropy when the c-axis in them are well oriented.

Preparation of perpendicular magnetic recording media by DC magnetron sputter roll-coating

Preparation of perpendicular magnetic recording media by dc magnetron sputter roll-coating is described. PET film is used as the base film of a double-sided double-magnetic-layer medium. To maximize the output, magnetic properties of both the Co-Cr layer and the underlayer are investigated under the restricted condition imposed by the low heat resistivity of PET film. By adding a small amount of N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas during sputtering, optimum coercivity of the underlayer is obtained with a good balance between high output and low modulation. We determined that a low degree of crystal orientation in the underlayer yields a high vertical coercivity of the Co-Cr layer and that a thin Co-Cr-O intermediate layer increases the output. Two techniques for reducing the curling of the medium are also adopted. Further improvement of the media and the head/medium interface is needed because of surface degradation and insufficient durability.

On improved durability characteristics for a Co-Cr flexible disk system

The signal durability of a disk which was formed by sputtering Co-Cr, permalloy, and inorganic protective layers on both surfaces of a flexible substrate was studied by evaluating its tribological characteristics. Out-put signal loss in proportion to head-pass number was found to be due to brittle fracture and/or plastic deformation of the disk. A disk with plastic deformation showed better signal durability than that with brittle fracture. High toughness and homogeneous structure of metal layers presumably improve durability for the practical use of a Co=Cr layered flexible disk system.

The influence of nitrogen and other gases on the magnetic properties of bias-sputtered Co-Cr perpendicular films for computer memory applications

This paper investigates the effect of negative bias on sputtered CoCr layers for hard-disc memory applications. Negative bias can significantly improve the C-axis orientation and the perpendicular magnetic properties. Oxygen and Nitrogen in particular degrade the desired properties but Hydrogen can have a beneficial effect at low concentrations.

Switching mechanism of Co-Cr films with Ge underlayer

The switching mechanism of a highly oriented Co-Cr single layer film with a Ge underlayer was investigated by measuring R/W characteristics, observing the Bitter pattern of recorded magnetization and head field calculation by finite element method. To clarify the relationship between magnetization reversal and head field intensity, overwrite signal to noise ratio and asymmetry ratio of two adjacent hits output amplitude were measured. To analyze the switching mode of this film, Bitter patterns of the recorded medium on the top and the bottom surfaces with different write currents were observed. From these results, it is concluded: (1) Complete magnetization reversal can be achieved when the head field in the perpendicular direction is greater than Hc\perp × 1.2 at the bottom of the Co-Cr layer. (2) This film is easily magnetized through the direction of depth, but degradation of the perpendicular head field distribution affects perpendicular magnetization penetration.