Characteristics of barium ferrite tape for magnetic contactduplication

The magnetic properties and electromagnetic characteristics of Ba-ferrite tape for R-DAT magnetic contact duplication (MCD) were investigated. The tapes employed Ba-ferrite particles averaging 0.06 μm in diameter with an aspect ratio between 4 and 5. Ba-ferrite tapes were prepared with perpendicular, longitudinal, and no orientation, and their MCD and ring-head recording (RHR) characteristics were compared. Several distinctive characteristics were observed in MCD, and the desirability of perpendicular orientation at short wavelengths in MCD applications is clear. Tilted orientation was also investigated, and its output level was similar to that of perpendicular orientation in MCD, while in RHR it proved superior to perpendicular orientation in the short wavelength region. The magnetization mode of the slave tape was studied by waveform analysis using the FFT method and in conjunction with the tapes' magnetic properties, such as uniaxial anisotropy energy, remanence coercivity, and squareness ratio     

Remanence properties of substituted Ba-ferrite particles for highdensity magnetic recording

In this paper, the remanence properties of Co-Sn, Co-Ti and Co-Ti-Sn substituted Ba-ferrite (BaF) oriented particulate samples are compared with those of some oriented acicular particulate samples. A new parameter, the minor remanence distribution (MRD), is proposed to review the remanence properties of magnetic particles and the capabilities for resisting the recording demagnetization of magnetic recording media. It is shown that the MRD values of the oriented BaF particulate samples were smaller compared to oriented Co-γ-Fe₂O₃ samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-γ-Fe₂O₃ samples. It Is the small MRD, SFD_r, IRS and large DH _r of a medium that can result in a large resistance to the effects of recording demagnetization and therefore in superior characteristics for high density magnetic recording. Since Co-Sn substituted BaF platelet-shaped particles exhibit these characteristics and have a very low temperature coefficient of coercivity, these particles can be expected to be a promising candidate for high density magnetic recording     

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.     

Perpendicular magnetic recording

This paper describes the recent studies for the magnetic head, the medium and the recording properties on a new perpendicular magnetic recording system. The complemental features between the perpendicular and the longitudinal recording are discussed to establish an efficient magnetic recording system. Superior response in the amplitude and the peak shift characteristics for a digital signal proves that the perpendicular magnetization mode is basically free from the recording demagnetization in high densities and the maximum density has been limited merely by the resolution of the reproducing head. Significant improvement for the recording and the reproducing sensitivities of a perpendicular head has been made by using a composite anisotropy medium composed by double layers of Fe-Ni and Co-Cr thin films.     

Rare earth - transition metal alloys: Another way for perpendicular recording

Many investigators have chosen CoCr alloys or other Co-based alloys to study perpendicular magnetic recording. Although the perpendicular magnetic anisotropy of Co alloys is quite convenient for this use, the demagnetizing fields are high because of high saturation magnetization and then the squareness of the perpendicular M-H loops is poor. To study another kind of perpendicular anisotropic alloy, we tested sputtered amorphous Fe1-x-yTbxGdy(X = y) thin films as a perpendicular recording medium. Several thicknesses with and without a FeNi underlayer were tested. Although a conventional ring-type head was used, with a low trackwidth (20 μm) and a coil with 2 × 13 turns, 162 KFci could be recorded and read and a 1,600 μ Vpp output signal was read at 10 KFci.     

Influences of sputtering gas pressure on microtexture and crystallographic characteristics of Ba-ferrite thin films for high density recording media

Ba-ferrite films with small c-axis dispersion angle Δθ50are suitable for ultrahigh density recording media. The dependences of partial oxygen gas pressure PO2and total discharge gas pressure PTotalon the characteristics of Ba-ferrite films were clarified. It was found that there were three regions, where films were composed of single layer of spinel type ferrite(PO2≤0.002mTorr), mixed layer of spinel and magnetoplumbite type ferrites (0.003 leq P_{O2} leq 0.2mTorr) and single layer of magnetoplumbite type ferrite (PO2>0.3 mTorr). In the range of P02between 0.005 and 0.2 mTorr, spinel-like ferrite layer plays very important role as an underlayer to decrease the Δθ50of the Ba-ferrite layer. Films deposited at relatively low PO2and PTotalexhibit very smooth surface and Δθ50as small as2.5sim3.5deg.     

Optimization of Precompensation for NLTS in Perpendicular Magnetic Recording

Nonlinear transition shift (NLTS) and nonlinear amplitude distortion (NLAD) in perpendicular magnetic recording were investigated for CoPtCr-SiO$_2$media with various SiO$_2$contents that have various inter-granular exchange coupling. The tighter inter-granular coupling increases both NLTS and NLAD. The NLTS and NLAD were discriminated and extracted NLTS showed that perpendicular media exhibited the opposite shift to longitudinal media as theoretically expected. Careful precompensation optimization is required to obtain a good error-rate performance at high-linear densities.     

Control of M-H Loop Shape in Perpendicular Recording Media by Ion Implantation

We have investigated the properties of CoCrPt-SiO₂ perpendicular recording media as influenced by Co ion implantation, and have shown that a substantial change of the M-H loop squareness and a control of coercivity (H_c) over a wide range are feasible. Thin films of Ta(5 nm)/Ru(20 nm)/CoCrPt-SiO ₂ (15 nm) were deposited and then subjected to the ion implantation with various acceleration energies, doses, and incident angles. It has been found that the cobalt ion implantation significantly alters the magnetic properties of CoCrPt-SiO ₂. In the case of the near-perpendicular implantation at 60 KV, the M-H loop became much squarer but there was a decrease of coercivity 4300 to 2100 Oe. There was no noticeable decrease of the saturation magnetization by implantation. The reason for the significantly increased squareness by near-perpendicular implantation is mainly attributed to the increase of exchange coupling between the grains by cobalt ion implantation     

The effect of thickness on the texture and magnetic properties of single-layered FePt films by rapid thermal annealing

The single-layered FePt films with thickness in the range of 5 to 50 nm are deposited directly on Si(100) substrate without underlayer, then post annealed at 700 degrees C by rapid thermal annealing (RTA) technique. As the film thickness of FePt is over 20 nm, the L1(0) FePt(111) preferred orientation is presented and tended to in-plane magnetic anisotropy. However, the L1(0) FePt(001) texture is obtained and exhibited perpendicular magnetic anisotropy as the film thickness is decreased to 10 nm. Its perpendicular coercivity (Hc(perpendicular)), saturation magnetization (Ms) and perpendicular squareness (S(perpendicular)) are 14.8 kOe, 795 emu/cm3 and 0.79, respectively. On the other hand, both the grain size and domain size of FePt film decrease with decreasing the film thickness of FePt. The grain size for 10-nm FePt film is as small as 9.7 nm with domain size of 123 nm, which reveal its significant potential as perpendicular magnetic recording media for ultra high-density recording.     

The promise of new particulate media for high density recording

The superiority of perpendicular recording derives from the very low demagnetization at high bit densities, and from the nearly perfect writing process when a single pole head is used in combination with a double layer medium. Recent experiments have shown that it is possible to record very high densities in the longitudinal recording mode by scaling down all the critical parameters to extremely small values. However, such extreme scaling will very likely be accompanied by some very difficult problems from the point of view of media imperfections, defects, yields and costs. The power of perpendicular recording derives in part from the ability to attain these very high bit densities without resort to extreme scaling of the critical system parameters. There is little doubt that in the long run perpendicular recording will predominate because of its superior performance derived from the advantages stated above. For the next several years, however, we have to look to new and improved particulate media (to satisfy the majority of the demands) which can be fabricated by using existing large capacity continuous web coating facilities. The best choice for satisfying the requirements of these tape-related large volume applications is to utilize the new particulate media which support a large degree of perpendicular magnetization (isotropic-high squareness, and perpendicular anisotropy particulate dispersions) rather than employing very high coercivity longitudianally optimized particulate media.     

Microstructures and magnetic anisotropy of single-layered Fe-Pt alloy films by in-situ annealing

The single-layered Fe-Pt films with thickness of 30 nm are in-situ deposited directly on Si substrate at various substrate temperatures (Ts) of 350 to 590 degrees C. As the Fe-Pt film is sputtered at substrate temperature is 350 degrees C, it shows (111) preferred orientation and tends to in-plane magnetic anisotropy. The L1(0) Fe-Pt film with (001) texture is obtained and exhibited perpendicular magnetic anisotropy as the substrate temperature is increased to 470 degrees C. The perpendicular coercivity (Hc perpendicular), saturation magnetization (Ms) and perpendicular squareness (S perpendicular) of this film are 6.9 kOe, 674 emu/cm3 and 0.89, respectively, which reveal its significant potential as perpendicular magnetic recording media.     

FePtAg-C纳米颗粒薄膜的制备及表征

采用磁控溅射法在硅基片上生长FePt纳米颗粒薄膜。在硅片表面生长MgO籽层用来引发FePt合金薄膜的fct织构,加入C来减小其颗粒尺寸,加入Ag来增强其L10有序度。采用X射线衍射仪（XRD）、超导量子干涉仪（SQUID）和高分辨率透射电镜（TEM）对FePt薄膜进行表征。结果表明制备的薄膜样品具有优良的L10相结构,其M-H曲线表明方形度很好,垂直矫顽力HC有2467 kA/m,颗粒大小为10.4 nm。该薄膜非常适合用做下一代高密度磁存储媒质,可有效提高信息存储密度。     

Perpendicular magnetic recording -- Evolution and future

This paper reviews research results for the head, medium and recording properties of a perpendicular recording system. Superior bit density characteristics obtained so far indicate that perpendicular recording is basically free from demagnetization in the high density region and that it will establish a new field of recording technology in the future. The prediction is explained in the context of complementary profiles of longitudinal and perpendicular recording. At the very beginning of magnetic recording, a perpendicular-type head was considered but abandoned because a suitable medium did not exist. Progress in material science has enabled us to develop a perpendicular recording medium which is very well suited for ultra high density recording. As so often happens, history has repeated itself through another study of perpendicular recording.     

Recording characteristics of electroless-plated perpendicularrecording flexible disks with a perpendicular head

Perpendicular magnetic recording using a main-pole-driven perpendicular head was tested using electroless-plated flexible disks. Soft magnetic NiFeP films, also produced by electroless plating, were used as an underlayer of a perpendicular recording medium in this test. Two types of flexible double-layer media, composed of an electrodeless-plated CoNiReP film with two types of NiFeP underlayers with a coercivity of 2 and 5.5 Oe, were fabricated, and their recording characteristics were measured. A recording density value of 75 kFRPI was obtained for the medium with the softer magnetic 2-Oe underlayer, about twice as high a value as that for the medium with the 5.5-Oe underlayer     

Magnetic alumite disc for perpendicular recording

Details of making are given of perpendicular magnetic alumite, discs obtained by an aid of anodization with the additional new process named "pore widening" which was effective to control the coercive force. The electrodeposited fine iron needles were in single crystalline state. The perpendicular orientation of magnetization was confirmed. The magnetic recording, characteristics of rigid discs indicated a hilgh potential for use as a perpendicular recording medium.     

Plasma effects on the Co-Cr deposition in opposing targets sputtering method

It is well known that Co-Cr films show a high perpendicular magnetic anisotropy, coercivity of 1000 oe or above and other properties suitable for perpendicular magnetic recording media. In this report, Co-Cr films, deposited by the bombardment of ions extracted from plasma using a new type of cathode sputtering apparatus with opposing targets, which will be called opposing targets sputtering hereafter, were investigated on morphology, crystal structure and magnetic properties. It was found that in the Co-Cr films of suitable magnetic properties for recording media, the morphology changes and the degree of C-axis orientation of Co-Cr hcp crystal, Δθ50is a constant value as low as about 3° with the increase of ion bombardment energy during deposition. Both morphology and the dependency of Δθ50on thickness of the Co-Cr films deposited by the opposing targets sputtering considerably differ from those by RF sputtering. There was no columnar structure observed in the cross section of the Co-Cr films suitable for perpendicular magnetic recording media prepared by the opposing targets sputtering, whereas columnar structure is reported to be observed clearly in the case of both RF sputtering and vacuum vapor deposition.     

Structural, magnetic, and magneto-optical properties of nanocrystalline face centered cubic Co70Cr30/Pt multilayers with perpendicular magnetic anisotropy

Co70Cr30 alloyed layers are combined with extremely thin Pt layers in order to produce novel face-centered-cubic multilayered films to be considered as a potential perpendicular magnetic recording medium. The films were grown on Si, glass and polyimide substrates by e-beam evaporation at a temperature slightly higher than room temperature. The multilayered structure of the films was verified by X-ray diffraction experiments. Plane-view transmission electron microscopy images have revealed the formation of very small grains in the range of 7-9 nm. Hysteresis loops as a function of temperature were recorded via the magneto-optic Kerr effect in the polar geometry configuration. The system exhibits perpendicular magnetic anisotropy, which enhances with decreasing temperature. Hysteresis loops with a squareness of 1 and a coercivity of 1.45 kOe were obtained at 10 K. Furthermore, complete magneto-optic spectra of the films are recorded, showing a strong magneto-optic enhancement in the ultraviolet region at around 4.5 eV.     

Effect of Ag underlayer on microstructures and perpendicular magnetic properties of CoPt nanocomposite thin films

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of degree of ordering and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a large degree of ordering and a perpendicular magnetic anisotropy after annealing at 700 degrees C for 30 min. CoPt/Ag films with out-of-plane coercivity (Hc (perpendicular)) in the range of 13.5-14.0 kOe and a out-of-plane squareness (S(perpendicular)) of 0.97 were obtained after annealing at 700 degrees C for 30 min. Ag underlayer is beneficial to enhance the Hc(perpendicular)and S(perpendicular) of CoPt film significantly. The degree of ordering and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.     

Orientation of magnetic particles in a recording medium

The theory of the motion of magnetic particles in a viscous Newtonian medium, first outlined by Newman and Yar-brough, has been extended to include both low and high field orientation modes. It is shown that the equations of motion can be solved analytically, i.e., without resort to numerical integration. The results of the analysis are used to predict values for easily measured parameters of recording media, such as the initial remanence ratio and squareness ratio.     

Study of peak shift in thin recording surfaces

One of the most severe limitations on high-density digital recording is imposed by peak shift, which is defined as the outward displacement of the readback signal peaks corresponding to a recorded bit pattern of two successive ones followed and preceded by a number of zeros. Results of an experimental study of peak shift in thin metallic media are represented along with a correlation of the measured percent peak shift with the magnetic properties and the thickness of the media. It was found that the percent peak shift at a specified bit density varies proportionally with the thickness of the coercivity ratio for coercivities larger than 250 Oe. For lower coercivities, the remanent magnetization of the recording surface becomes increasingly significant in adversely affecting the peak shift, with a corresponding decrease in the importance of thickness. By superposing isolated pulses it was possible to predict the percent peak shift up to extremely large bit densities.