MAGNETIC THIN FILM DATA STORAGE MEDIA

Abstract: A chromium underlayer is provided under Co-Ni films used for magnetic recording; for "high Hc" and "good squareness", a Cr thickness of about 1000 A DEG or more is preferred with 400 A DEG - 5000 A DEG Co-20 Ni. The thickness of the Cr layer is selected to obtain a coercivity that provides both high recording density (small PW-50) and acceptable overwrite. The techniques described here show that an adjustment of the epi-orientation influence of a chromium underlayer can yield a thin cobalt-nickel magnetic film of moderate Hc and so accommodate a recording medium having high magnetic recording density and satisfactory overwrite capability.

Description: TITLE MAGNETIC THIN FILM DATA STORAGE MEDIA This concerns magnetic layer and underlayer thickness optimization, especially those like cobalt- nickel and chromium as deposited films for digital (magnetic) recording and particularly their relationship to recording performance. —Background, Features of Novelty: Workers in the magnetic recording arts are aware of the advantages of using thin film media (e.g., .as opposed to particulate media); e.g., to achieve high linear recording density. For instance, Co-Ni films make excellent longitudinal recording media. This relates to the proper selection of the properties of Co-Ni layers to achieve acceptable recording performance. The usability of a recording medium depends on the output voltage, signal to noise ratio (S/N) , overwrite characteristics and "single pulse half width" (PW-50) for a given type of head. The coercivity, thickness, switching field distribution, squareness and saturation magnetization of a medium are intimately related to its recording performance. For example, given a certain media thickness, increase in coercivity will improve the PW-50 but will adversely affect the over-write, On the other hand, if the coercivity is kept constant, a decrease in magnetic layer thickness degrades voltage output and S/N, but improves over-write and PW-50. In the past, oxide and plated media have been used for high density digital recording. Particulate oxide media is approaching the limit of decreasing magnetic layer thickness in order to obtain improved coercivity (PW-50) and OVW, since the signal output lowers and degrades S/N (the signal to noise ratio) .' Plated media has poor commercial acceptance due to inconsistent quality and concern over corrosion. Table I below shows the difference in their performance compared with a typically-sputtered medium. It is evident that sputtering provides a flexibility in constructing a medium with optimized properties — and, in particular, that the magnetic properties of a sputtered magnetic layer can be tailored by a suitable unde-rlayer. This we propose here, TABLE I * 5>s Rigid Disk , "OD" 2.4 in R, "ID" 1.3 in R, Recording Magnetic Recording Media Type Performance Particulate Plated Sputtered Characteristic Co.P Fe 2°3 Co/Ni on Cr 10. Linear Recording Density KFCI 12 12 to 16 14 to 18 Relative Output fODIF 0.93 2.9-0.97 4.2-1.40 \ID2F 0.47 1.8-0.60 2.2-0.67 Signal/Noise . 1.4" R -34 -37 -37 . 5 (SNR dB) Resolution (OD. 93 98 97 I IΌ% 83 97 91 OVW (-dB) 31 33 32 PW-50 §2.0" ("ns 130 90 105 0 (_uin. 98 68 79 Magnetic Properties Coercivity, Oersted 300-600 400-900 400-1000 Squareness .7 to .8 ^.8 8 Saturation, Magne¬ 5 tization, gauss 1350 ** 18000 15000 Magnetic Layer Thickness uin 35 2.5 2 to 3 * Using M2F head, ->35 uin. gap, 12 uin F.H. at 5-00 ips. ** 30% loading. Here, we are assuming the following: OVW* degrades with increasing coercivity** and increasing magnetic film thickness; however. Recording density*** increases with increasing coercivity and decreasing magnetic film thickness, and, Reajd-back signal amplitude increases with increasing coercivity and increasing magnetic film thickness. Hence, these three required performance characteristics are dependent on magnetic film properties that are in conflict. What is needed is an optimization of coercivity, H , and magnetic film thickness. We have developed a method to adjust the H of films that are thick enough to give good signal and at the same time allow high recording density and better overwrite. In this work we describe how the selection and mechanism of the underlayer film thickness optimizes recording performance over a range of magnetic film thicknesses. * OVW, overwrite, is defined as the logarithmic ratio of amplitude of the residual IF signal after it is overwritten by a 2F signal (compared to the original IF amplitude) . ** Coercivity, H , is the magnitude of applied field needed to return saturated magnetic material to a condition of zero remanent moment. *** Recording density is measured by the single pulse width, PW50: A narrow or small PW50 gives better recording density. Here, we propose an underlayer (e.g., Cr) be used in conjunction with a magnetic layer (e.g., Co-Ni) to vary the magnetic properties of the magnetic layer as desired1 It was found that the thickness pf a chromium underlayer strongly influences the growth of a Co-Ni overlayer which changed its magnetic properties as a result. Keeping magnetic layer thickness constant, different magnetic properties (in particular coercivity and squareness) could be achieved by controlling underlayer thickness and construction (e.g., texture). A range of magnetic layer and underlayer structure' and thicknesses are found to optimize recording performance. Brief Description of the Drawings: These and other features and advantages of the present invention will be appreciated by workers as they become better understood by reference to the following detailed description of the present preferred embodiments which should be considered in conjunction with the accompanying drawings, wherein like reference symbols denote like elements: FIG. A is a very schematic section through an underlayer and overlying magnetic film embodiment; FIGS. 1, 2, 3 and 4 plot variations in coercivity (He), Overwrite(OVW) , Pulse half-width -(PW-50) and Signal Output (ODIF, ID2F) , respectively, with Co-Ni magnetic film thickness; FIGS. 5 and 6 depict variations in OVW, and PW-50 with He; and ° FIG. 7 plots variations in He vs. chromium underlayer thickness with Co-Ni thickness for optimized discs. Description of the Preferred Embodiment —General description, background: FIG. A schematically illustrates a chromium underlayer 3 constructed according to principles of this invention. This, and other films and materials discussed herein, will generally be understood as constructed and operating as presently known in the art, except where otherwise specified. And, except as otherwise specified, all materials, methods and devices and apparatus herein will be understood as implemented by known expedients according to present good practice. —Co-Ni films in general: Our initial Examples (below) are directed toward Co-Ni films. Sputtered Co-Ni thin films are believed excellent candidates for advanced longitudinal magnetic media [e.g., see R.D. Fisher, MRM "83 International Conference on Magnetic Recording Media, Ferrara, Italy, Sept. 1983; L.F. Herte and A. Lang, Jr., J. Vac. Sci. Tech., 18, No. 2 1981, pp. 153-155; R.D. Fisher, L. Herte, A. Lang, IEEE Trans. Mag., Vol. MAG-17, No. 6, 1981, pp. 3190-3192; and H. Maeda, J. Appl. Phys. , 53 (10), 1982, pp. 6941-6945]. Workers appear to have suspected that a chromium underlayer might enhance some aspects of a magnetic film, but didn't know exactly why, or exactly how, to quantify this relation (e.g., no hint that a certain Cr thickness might optimally affect a certain Co-Ni thickness; what effect film texture, or microstructure might have, etc.). The magnetic properties of thin Co-Ni films are largely dependent on the preferred orientation of the film. High coercivity of Co-Ni alloy films can be obtained when the strong preferred orientation of these films with the C-axis parallel to the film plane. It also seems that changes in underlayer texture affect the magnetic properties of magnetic (e.g., Co-Ni alloy) films However, the correlation between crystal texture and magnetic properties of thin films is not well established We have determined the effect of crystal texture on magnetic properties of relatively thin, "hexagonal close packed" (HCP) Co-Ni films. Such films of various thicknesses were sputter deposited on different types of substrates as a factor in the mechanism of Co-Ni film growth. The in-plane coercivity, squareness ratio and M-H hysteresis loop are also discussed as a function of thickness for different films as well as their crystal textures. —Other approaches: FIG. A will be understood as depicting a thin fil longitudinal magnetic recording structure (shown only fragmentarily, in section, and. idealized) comprising a substrate 1 (flexible or rigid) on which is placed an underlayer 3 with a thin magnetic film 5 (e.g., for digital recording) , superposed on the underlayer 3. Such a magnetic film°5 may be understood as deposited (e.g., sputtered) to a depth of about 0.03-0.5 um (i.e., 300-5000 A°). Underlayer 3 is here intended to enhance magnetic properties; it will be about 400-10000 A β thick (.04-1 um) . Sputtered Co-Ni films (.03-0.1 um) with no underlayer have a relatively low coercivity, e.g., about 200 Oe (this is undesirably low for high density digital magnetic recording; e.g., 20,000 fc/i or more is typically desired; also see article by H.J. Lee and D. Baral in IEEE Trans. MAG-21 (5) 1477, Sept. '85. Some have suggested a sputtered underlayer of chromium for various purposes (see L.F. Herte and A. Lang, J. Vac. Sci. Technol. Vol. 18, No. 2, page 153, 1981); or one of molybdenum (see K.Y. Ahn, K.N. Tu, IBM TDB, Vol. 21, No. 10, 4232, 1979), e.g., to achieve "high" coercivities (i.e., 500 Oe or more). We had surmised that the He of cobalt alloys will vary with the thickness of the Co layer (and possibly Cr underlayer) , but this came only from laboratory investigations with no application to commercial, practical high speed magnetic recording. We teach, here, that for such a sputtered film 5, one should specify an underlayer 3 of prescribed corresponding thickness (according to materials involved) to assure an enhanced reproducible recording performance. For instance, we find that the coercivity of such Co-Ni films on a Cr film underlay is strongly dependent on Co-Ni crystalline orientation and grain size as determined by the Cr thickness. The introduction of the thin film head (TFH) to magnetic recording technology has placed new demands on media performance; namely, increased output signal level, and improved overwrite (OVW) . Current thin film media satisfy signal strength; however, improved OVW usually requires one to sacrifice recording density (i.e., bit . size, bit density) represented by single pulse half width, PW-50) . Therefore, present day disk drives continue to use ferrite recording heads (MZF) to obtain satisfactory OVW, even though a TFH would improve areal recording density and lowers costs. Though it might be more conventional to use a chrome underlayer 3000 to 4000 A β thick, we find that to obtain improved signal (OVW and PW-50 simultaneously) , one needs to reduce the underlayer thickness. Other workers have related materials and construction to magnetic characteristics,•but we find that recording performance depends not only on the thicknesses of the magnetic film and the corresponding underlayer film, but also on their construction. We propose media characterized by a Co-Ni construction and thickness range giving good signal output, and a corresponding chromium thickness and construction (texture) that ameliorates the resulting coercivity (He) — to thereby secure desirable OVW and PW-50 (overwrite and bit density) . For instance, we propose using freshly sputtered chromium (0.04 to 0.2 um) as an underlayer to give high in-plane coercivity for a specific thickness range of Co-Ni (0.03 to 0.1 um) . Co-20 Ni over 0.08 um CR: A range of Co-Ni thicknesses (0.03 to 0.10 um) is sputtered on various chromium underlayer thicknesses (0.04, 0.08, 0.14 and 0.20 um) , with 1/2 inch square coupons of disc material and 5k diameter rigid discs, both serving as substrates. The deposition is done at 10 mTorr argon pressure using "D.C. magnetron" sputtering (otherwise assume normal processing, e.g., at room temperature) . The in-plane magnetic properties are measured with a vibrating sample magnetometer. The variations in coercivity are shown in FIG. 1 for various Co-Ni thicknesses for each of the Cr underlayer thicknesses. The results (FIG. 1) indicate that coercivity decreases as the Co-Ni film thickness increases from 400 to 900 A β , for all of the chromium thicknesses (Cr 400 to 2000 A β )„ Also, decreasing the Cr underlayer thickness uniformly lowered He at each Co-Ni thickness. Recording performance for each disc fabrication was evaluated on a disc certifier using a mini-Winchester type manganese-zinc-ferrite (MZF) recording head flying at 12 u-inch (at 500 IPS), using a "IF" signal (1.25 MHz at 2.4 inch is OD on outer track) and "2F" signal (2.5 MHz at 1.3 inch is ID). [As workers know OVW represents the ratio in dB of overwritten signal outpu to original, underlying signal IF, both "bit dimensions" being the same] . The variation of OVW, PW-50 and signal output with Co-Ni thickness is shown on FIGS. 2, 3, 4 respectively. FIG. 2 shows a desired maximum OVW (greater than -32.8dB) occurring between 400 to 1000 A β Co-Ni for each of the Cr thicknesses (400, 800, 1400 and 2000 A°) selected. FIG. 3 shows values of PW-50 decreasing with Co-Ni thickness and also decreasing as Cr thickness increases, for each Co-Ni thickness. FIG. 4 depicts a maximum signal output voltage at 700 A 0 Co-Ni and a fall-off to below the desired minimum 650 uv at the ID about 300 A° and then at 900 A° Co-Ni. The dependence of OVW and PW-50 on He will be evident in FIGS. 5 and 6 respectively. These FIGS, help make our point that optimized thickness of the magnetic film and its underlay can help achieve better OVW (higher) , PW-50 (lower) and signal amplitude (higher) . Results: We find that the thickness of a Cr film is a measure of the epitaxial influence the Cr has on orientating Co-Ni deposited thereon, and that Cr thickness controls the "thickening" of its morphological columnar growth {this influences Co-Ni grain size ) . A lso, as Co-Ni thickness increases, the Co-Ni grains get larger, thus lowering He. In order to maintain He, we increase the thickness of the Cr underlayer to promote texture and in-the-plane orientation of Co-Ni that offsets the increase in gra^Ln size. It is recognized that crystalline anisotropy is the primary magnetic means in the recording mechanism of thin film. We have found that the saturation of "poly-oriented" crystalline Co-Ni film occurs at a lower applied magnetic field than when the orientation is predominantly in the plane. Saturation recording on a Cr substrate film is strongly dependent on Co-Ni crystal orientation and grain size as determined by appropriate thickness of the Cr underlayer for associated Co-Ni thicknesses. Now, a reduction in underlayer thickness would be attractive economically (e.g., less running time and material consumption during production) , as workers well know. This is possible with our teaching. When specified OVW of -32.8 dB and 120 ns PW-50 are both required, it can be seen (FIGS. 5 and 6) that one needs media coercivity of 400 to 600 Oe. This He range translates to a 400 to 700 A β Co-Ni thickness. FIG. 7 plots He and Cr thickness for optimum performance discs. These results indicate that, since a minimum thickness of 300 A β Co-Ni is required for > 650 uv signal, an underlayer of 400 A° Cr would be needed to keep He between 400 to 600 Oe and achieve the desired PW-50 ( <.120 ns) and OVW (<-32.8dB). A thickness of 1000 A° Co-Ni appears to reduce the practical signal output to <£, 600 uv (FIG. 4). It is noted that optimum OVW and PW-50 can be obtained for selected Co-Ni and Cr thicknesses beyond those prescribed here, but a compromise on signal output must be made. FIG. 7 allows selection of a Cr underlay thickness for any value of Co-Ni thickness between 400 and 900 A β . The Cr thickness needed for a given Co-Ni thickness to obtain the performance benefits described here must be obtained from the relationship: Cr thickness = 3.7 X Co-Ni thickness - 1175 in A° (i.e., t = 3.7 t__ n - 1175, in a AA β ; where t "?"300) • c-n TABLE II Optimized Discs Required Cr Co-Ni, Thickness A" Thickness A β 519 745 603 1056 701 1419 1000 2525 In summary, to achieve OVW <-32.8 dB, PW-50 - 120 ns and signal output ^600 uv, using an MZF head flying at 12 uin, we advise: TABLE III Media He: 40° to 600 Oersted Co-Ni thickness: 300 to 1000 A β (preferably 400 to 900 A β ) Cr underlayer thickness: 400 to 4000 A β (preferably 700-2200 A β ) For performance optimization the Cr underlayer must be at least 700 A° thick for He control and Co-Ni at least 400 A° thick for sufficient signal strength. When Co-Ni is thicker than 500 A°, the following relationship gives the necessary Cr thickness in A° : Cr thickness = 3.7 X Co-Ni thickness - 1175. The magnetic properties (e.g., coercivity and squareness) of thin Co-Ni films seem largely controlled by the texture (preferred orientation) and the micro- structure (grain size) of both films (Cr affects Co-Ni growth) . In our work, a Cr underlayer plays an important role in the growth of Co-Ni film texture, especially [loll] preferred orientation. This [1011] Co-Ni texture ' usually gives relatively higher in-plane coercivity because of hard axis orientation of magnetization in HCP structure. However, beyond [1011] texture, the coercivity of Co-Ni films (on Cr) is strongly dependent on the grain size of [loTl] crystallites. The smaller the grain size, the higher the coercivity. This has been seen, for example, in Co-Ni films of > 400 A*. As thickness of a Co-Ni film increases (a thicker film always has larger grain size if deposition conditions are constant) , He will decrease due to the "grain size" effect. The reason that a " 300 A β Co-Ni over Cr" film exhibits lower coercivity than a *' "^400 A° Co-Ni over Cr" film is that it doesn't have the [loll] texture, though it has smaller crystallites. Dependencies: OVW will depend on the recording head employed; while signal output will depend on head flying height, electronic amplification and signal processing; therefore, it is likely that the Co-Ni thicknesses and the corresponding Cr thickness range specified here can be extended. In any event, we have discovered that coercivity can be quantitatively related to a Co-Ni thickness and Cr thickness, and that there are multiple Co-Ni and chrome thicknesses where acceptable OVW and PW-50 are obtainable; for instance, for Co-Ni 400-700 A°, with Cr 800-2200 A β . Such Cr underlayers are preferred for all like magnetic thin films (e.g., all Co-Ni alloys over thicknesses from 500 to 5000 A β ; and coercivities from 300-700 Oe) . The chromium laid down should be relatively pure (e.g., above 90%, with no more than 10% other metals, oxide, etc.); and should be less than about 1 um thick. Cr underlayers are also contemplated for other magnetic films, especially other alloys of Co and Co-Ni [e.g., Co-Cr, Co-Ni-Cr; and Co-Pt and Co-Ni-Pt] . In some cases a number of superposed Cr underlayer thicknesses will be feasible (to render same total Cr thickness) . e find that many substrates (for Cr underlayer) seem satisfactory, especially a metal like that of the well known aluminum Winchester disk (e.g., polished flat, possibly oxidized, but -never anodized, else it may pit; and sometimes with nickel-phosphorous super-plating to harden) . In some cases a glass or thermally-stable plastic will suffice. Further advantages to so using such a Cr underlayer are: 1. Less minimum thickness of Cr is needed to obtain similar enhanced magnetic properties (e.g., 700 to' 2200 A° of Cr vs. 4000 A β Cr for non-optimized media). 1A. The thickness of Cr required to achieve ~500 Oe coercivity in super-coated Co-Ni is 1/4 (one fourth) that presently applied (conventionally) . 2. With the linear relationship found for He vs. Co-Ni thickness for each Cr underlayer thickness (FIG. 1) , one can relax deposition process control parameters. This can be important in light of an inherent thickness inhomogeneity that accompanies sputter deposition. 2A. Use of a prescribed Cr underlay thickness makes process control easier (cf. variation in the Cr thickness of 800 to 2200 A β accommodates a Co-Ni range of 400 to 900 A β ). We have found, surprising to say, that preferred Cr thickness t is related mathematically to a given Co-Ni thickness T _ as: t = 3.7 t - k in Angstroms, where k is about 1175 A°. This makes for a higher (bits/cm) recording density for the sputtered composite layer when an optimum Cr underlay thickness is used. 3. This "Co-Ni on Cr" composite structure can give rise to a thin film recording medium whose magnetic properties are more predictable, e.g., being more independent of film thickness variations (in Co-Ni thickness and/or underlayer thickness, even though the "Co-Ni on Cr" structure is relatively sensitive to variations in thickness of Co-Ni and of Cr) . One undesirable underlay material is: Iron (110 or 211) — for instance, an Fe layer under about 750 A β Co-Ni gave a miserable coercivity (about 42 Oe.; vs. bare aluminum giving in the neighborhood of 200 Oe.); whereas, a gold underlay (FCC) gave about 214 Oe. and tungsten gave about 555 Oe. One should beware of "galvanic cell" action developing from the substrate-underlayer-film combination or within any film thickness itself. For instance, Co-Ni combined with tungsten is apt to "self-destruct". Tungsten and iron seem very inadvisable (galvanic) additives to any magnetic film, but for anti-corrosion purposes, Co-Ni and Co-Cr are quite good. Also one may want to avoid combining aluminum with gold since one material seems to migrate into the other to give a relatively higher resistance alloy, etc. Variations: Workers will understand that the specific Co-Ni films discussed can be varied, or supplemented, as known in the art, while still deriving (at least some of) the advantages of using a chromium underlayer. Various thin metal (non-particulate) magnetic recording films are contemplated for such use; for instance, any cobalt or iron film, or their alloys (except phosphorous or selenium* alloys when sputtering is contemplated) — and for longitudinal or vertical recording (cf. Co-Cr with Cr underlayer for vertical recording) . And other deposition methods will at times be feasible, such as "wet chemical" (electroless- plating; electro-plating) and thermal vacuum evaporation. For instance, the desired magnetic properties can be varied, and/or they can be obtained (controlled) by control of deposition parameters (e.g., deposition rate, by using other sputter-atmospheres such as Ar-N. gas, or changing the surface temperature of the deposition substrate) , by adding alloy constituents or by using other "underlay-materials" like vanadium surprisingly (or like refractory metals) . Chromium, especially as described above, is preferred as an underlayer for ferromagnetic films like Co-20 Ni at the indicated thicknesses (about 300 to 1000 A°), particularly to achieve "higher" He (e.g., 500 ± 100 Oe or more) and reasonably "good" squareness (e.g. , 0.7 ± 0.1) . It will be understood that the preferred embodiments described herein are only exemplary, and that the invention is capable of many modifications and variations in construction, arrangement and use without departing from the spirit of the invention. For example, the means and methods disclosed herein are also applicabl to vertical reco2ding systems and the like, as well as to certain thin film heads. Also, the present invention is applicable for providing underlayers and magnetic supercoatings in other forms of recording and/or reproducing systems. The above examples of possible variations of the present invention are merely illustrative. Accordingly, the present invention is to be considered as including all possible modifications and variations coming within the scope of the invention as defined by the appended claims.

Claims: What is claimed is: 1. A digital magnetic recording structure for longitudinal or vertical magnetic recording with ferrite or thin film heads, this structure including a thin ferromagnetic record layer thickness, F, deposited on underlay film thickness, UL, disposed on substrate means, SUB; the thickness and structure of the underlay UL being related to that of magnetic layer F. 2. The structure recited in claim 1 as adapted for longitudinal recording wherein the thickness and crystalline structure of underlay film, UL, are prescribed and arranged to give moderately high coercivity, increased bit density, and good squareness in magnetic layer, F. 3. The structure recited in claim 2 wherein the thickness and structure of underlay film, UL, are adapted to control the texture, preferred orientation and magnetic properties of layer F, deposited on UL, the texture of UL controlling preferred orientation in layer F and its grain size. 4. The structure recited in claim 3 wherein the texture of a given layer thickness F comprises hexagonal close-packed cobalt-nickel of a texture and orientation induced by the texture and thickness of underlay UL to give thickness F a prescribed range of coercivity, squareness and remanent moment. 5. The combination as recited in claim 1 where layer thickness F is from about 300 to about 1000 A° Co-Ni, where film thickness UL is from about 400 to about 4000 A 0 Cr whose thickness and microstructure isj such as to control the crystalline structure and magnetic properties of thickness F, keeping coercivity at about 400-600 Oe. and inducing a 1011 structure therein. 6. The combination as recited in claim 4 wherein said thickness and structure of film UL is adapted to promote maximum bit density (minimum PW-50) and acceptable overwrite, OVW. 7. The structure as recited in claim 6 wherein the magnetic record layer F comprises from 300 or 400 to about 5000 A 0 cobalt-nickel and underlay film UL comprises about 400 to 1000 A°, to derive coercivity of 300 to 700 Oe. in layer F. 8. The combination as recited in claim 7 wherein 300 to 1000 A 0 of Co-20 Ni is used and is deposited on underlay UL to induce coercivity on the order of 400 to 600 Oe. or more, and squareness of about 0.6 to about 0.8 or more. 9. The combination as recited in claim 6 wherein the UL underlay is at least 90% pure chromium. 10. The structure as recited in claim 6 wherein the underlay UL is comprised of vanadium or a like refractory metal. 11. The structure as recited in claim 9 wherein both the Co-Ni and the chromium underlay are sputtered in one or more layers each. 12. The combination as recited in claim 1 where layer thickness F comprises Co or Fe, or an alloy thereof. 13. The combination as recited in claim _2 where underlay film thickness UL comprises Cr, V or a like refractory metal. 14. The combination as recited in claim 3 where layer thickness F comprises Co or Fe or an alloy thereof and film UL is adapted to induce a 1011 structure in thickness F deposited on UL. 15. The combination as recited in claim 14 where underlay UL comprises Cr of columnar-texture, adapted to induce a like texture in layer F deposited on UL. 16. The structure as recited in claim 1 wherein the underlay thickness T_- L in Angstroms is related linearly to that of the record layer T-,. 17. The structure as recited in claim 16 wherein the underlay UL comprises chromium and magnetic record thickness F comprises cobalt-nickel and wherein the chromium thickness T. U τ L τ .in Angstroms is several times the thickness Tr_ of the nickel-cobalt, less a constant K, in Angstroms. 18. The structure as recited in claim 17 wherein the constant K is about 1175 A β , and T... is 3 to 4 times T_, assuming the thickness T„ of cobalt-nickel is on the order of about 400 to 100-0 A 0 . 19. The structure as recited in claim 2 wherein the structure and thickness of UL are such as to derive acceptable OVW and PW-50 in magnetic layer F. 20. The structure as recited in claim 19 wherein layer F comprises a cobalt-nickel film of about 300 Oe. or more and the underlay UL comprises about 700 to 2200 A° of relatively pure chromium. 21. A ferromagnetic magnetic record structure including a magnetic recording cobaltous or ferrous layer F having a thickness of about a few hundred A° or more and an underlayer UL on a prescribed substrate SUB, underlayer UL having a microstructure and of sufficient uniform thickness to enhance the magnetic properties of the layer F which is deposited on UL. 22. The combination as recited in claim 21 where layer F comprises Co, Fe or an alloy of either. 23. The combination as recited in claim 22 where underlayer UL comprises Cr or V or a like refractory metal. 24. The combination as recited in claim 21 wherein the chromium is at least about 90% pure and comprises 400 A β - 1000 A β deposited onto a suitably flat substrate, 25. The combination as recited in claim 22 wherein the film is a magnetic recording cobaltous film having good squareness and relatively high coercivity, sufficient for high density recording. 26. The combination as recited in claim 25 where coercivity of layer F is about 400-600 Oe. or more and its squareness is about 0.6-0.7 or more. 27. The combination as recited in claim 26 wherein - • the layer is hexagonal-close-packed and comprises Co alone or alloyed with Ni, Cr, Ni-Cr, Pt or Ni-Pt. 28. The combination as recited in claim 27 where the layer is up to about 1 um of Co-Ni and the UL is 1000 A 0 or more of chromium, sufficient to optimize coercivity and squareness. 29. The combination as recited in claim 28 where the layer F comprises about 400-5000 A β Co-20 Ni, having a coercivity of 400 Oe. or more. 30. The combination as recited in claim 29 wherein the layer F is sputtered onto the Cr underlayer. 31. The combination as recited in claim 29 wherein the Cr is sputtered onto a suitable flat substrate. 32. A magnetic record structure comprising a few hundred A° or more of relatively pure chromium on a suitable flat substrate with a cobaltous ferromagnetic layer F deposited on the chromium, this layer F comprising at least several hundred A 0 of Co or Co-Ni or Co-Ni-Cr or Co-Ni-Pt or Co-Cr or Co-Pt. 33. The combination as recited in claim 32 wherein the cobaltous film is hexagonal-close-packed, and is adapted for high density magnetic recording, on the order of at least about 10-20 thousand fc/i; and wherein sufficient chromium is provided, and of a structure such as to induce a comparable structure F shown thereon, whereby to optimize the coercivity and squareness of layer F. 34. A method of fabricating a magnetic structure comprising: depositing a few hundred A 0 or more of mostly-pure chromium onto a suitable flat substrate; then depositing a few hundred A β or more of a magnetic recording metal film F onto the chromium; the chromium thickness and texture being such as to enhance magnetic record properties of the record film F; film F comprising cobalt or a cobalt alloy or iron alloy. 35. The method of claim 34 wherein the film F comprises Co or Co-Ni or Co-Cr or Co-Ni-Cr or Co-Pt or . Co-Ni-Pt. 36. The method as recited in claim wherein the cobaltous film F is hexagonal-close-packed,- is adapted for high density magnetic recording, on the order of 10-20 thousand fc/i; and wherein sufficient chromium is deposited to optimize the coercivity and squareness of the cobaltous film F. 37. The method as recited in claim 36wherein the chromium is at least- about 90% pure and sufficient is deposited to yield film F coercivity of about 500-600 Oe. or more, and film squareness of about 0.6-0.7 or more. 38. The method as recited in claim 37wherein up to about 1 um of Co-Ni film F is deposited on the chromium; and where about 1000 A β or more chromium is deposited on the substrate. 39. The method as recited in claim 38 wherein the film comprises Co-Ni. 40. The combination as recited in claim 39 wherein the film comprises about 400-5000 A° of Co-20 Ni. 41. The combination as recited in claim 39 where the Co-20 Ni film is sputter-deposited. 42. The combination as recited in clai 41 wherein the chromium is sputter-deposited. 43. A magnetic recording element comprising a few hundred A° or more of 90+% pure metal underlay UL deposited on a flat substrate, with a few hundred A° or more of a cobaltous or iron ferromagnetic record film F deposited onto the underlay UL, this film F being adapted for high density magnetic recording, having minimum coercivity of about 400-600 Oe. and minimum squareness of about 0.6-0.7. 44. The combination in claim 43 wherein the film F comprises Co, or Co-Ni, or Co-Ni-Cr or Co-Cr Or Co-Ni-Pt or Co-Pt and the underlay UL comprises Cr, V or 'a like refractory. 45. The product of the method recited in claim 34. 46. The product of the method recited in claim 36. 47. The product of the method recited in claim 37. 48. The product of the method recited in claim 38. 49. The product of the method recited in claim 39. 50. The product of the method recited in claim 40. 51. The product of the method recited in claim 41. 52. The product of the method recited in claim 42. ^^ • The product of the method recited in claim 34. where the underlay is vanadium or a like refractory metal. 5 # A method of fabricating a digital magnetic recording structure for vertical or longitudinal magnetic recording with ferrite or thin film heads comprising: depositing a prescribed underlay film UL on substrate means to exhibit a prescribed thickness and microstructure; then depositing a thin ferromagnetic recording layer F on film UL so that the thickness and microstructure of layer F are related to those of film UL whereby to determine magnetic recording properties. 55. The method of claim 54 wherein the thickness and structure of underlay film UL is controlled and provided to control the crystalline growth of layer F and its related magnetic recording properties, to exhibit high bit density, coercivity and squareness. 56. The method of claim 55 wherein the thickness and texture of underlay film UL is related to the desired magnetic recording properties of layer F and to the associated thickness and microstructure of layer F. 5 7 . The method of claim 54 wherein a relatively small underlay thickness T UL is provided to enhance magnetic recording properties like coercivity, squareness and moment Ms. 58 * The method of claim 57 wherein both UL and F are sputter-deposited. 0 59• The method of claim 54 wherein the thickness and microstructure of underlay film UL is arranged and adapted to control magnetic properties of magnetic layer F to be less dependent on thickness variations in either F or UL. 60. The method of claim 54 wherein chromium of at least 90% purity comprises underlay film UL and cobalt-nickel comprises magnetic layer F; wherein the texture and thickness of the chromium UL is adjusted and controlled to induce growth of a prescribed grain size and loll texture in the Co-Ni layer F such as to give prescribed preferred orientation and other magnetic properties. 61. The method of claim 6Q wherein the microstructure of the chromium film UL is columnar and that of the cobalt-nickel layer F is hexagonal-close-packed of a prescribed preferred orientation such as to facilitate high bit density longitudinal recording. 62. The method of claim ,61 wherein chromium thickness tcr is determined by the planned Co-Ni thickness ten according to the relation: tcr_. « 3.7 ten - K, in A β , where K is about 1150-.1200 A° , 6 3. The method of claim 60 wherein the order of 0.04 to 0.2 um of substantially pure chromium is sputtered onto a substrate followed by a related thickness and texture of Co-Ni whose microstructure is thus induced to exhibit a relatively high in-plane coercivity, the Co-Ni thickness being the order of 0.03 to 0.1 um. 64. The method of claim 5 wherein the layer F comprises at least 300-400 A 0 Co-Ni and the film UL comprises sputtered substantially pure chromium of relatively minimal thickness and of a microstructure adapted to induce' growth of a cobalt-nickel layer F of prescribed microstructure and thickness such as to exhibit prescribed tailored magnetic recording properties and such that variants in thickness of the chromium and/or Co-Ni has minimal effect upon these magnetic recording properties of the Co-Ni. 65. The method of claim 64 wherein layer F is formed to exhibit 400-600 Oe., OVW <-33 dB PW-50 < 120 ns and output > 600 UV with MZF head flying at 12 uin and 500 ips. 66. A method of fabricating a magnetic structure comprising depositing a non-magnetic underlay UL of chromium or vanadium or a like refractory metal upon a substrate and thereafter depositing a magnetic record layer F of cobalt or iron, or an alloy of either on this underlay UL such that the thickness and microstructure of the underlay UL affects related properties, including magnetic properties, of the layer F. 67. The method of claim 6 where UL is substantially pure Cr, layer F is Co-Ni, and the deposits are carried out so that the coercivity of the Co-Ni film F will vary relatively linearly with thickness for a given thickness of chromium-underlay. 68. The method of claim 7 wherein the UL and layer F are sputtered such that it is relatively easy to control and maintain prescribed magnetic recording properties despite variations in thickness of the underlay UL and/or of the magnetic layer F. 69. The method of claim 66 wherein, for longitudinal magnetic recording, the coercivity of layer F is optimized and controlled as a function of its thickness, there being sufficient layer thickness for good output amplitude. 70.. The method of claim 69 wherein the underlay thickness and microstructure is prescribed to induce formation of record layer microstructure such as to yield prescribed high bit density and OVW,. 71. The method of claim 9 where for a given record layer thickness, other recording properties, including squareness, are controlled according to the thickness and microstructure of underlay UL. 72. The method of claim 71 carried out to yield high OVW capability at relatively high bit density. 73. The method of claim 67 wherein the Cr underlay UL is from about 400 to about 4000 A β thick and the Co-Ni layer F is from about 300 to about 1000 A β thick, yielding coercivity of about 400-600 Oe. 74• The method of claim 73 wherein the Cr underlay is columnar lθ " ϊl and about 700-2700 A β thick while the Co-Ni layer F is hexagonal-close-packed and about 400-900 A° thick. 75 • The method of claim 74 wherein both UL and F are sputtered. 76. The method of claim 75 where the substrate is non-anodized aluminum or aluminum alloy.

Inventors: BARAL DEBASIS, HERTE LAWRENCE, LEE HYUNG JAI, VAN DE PITTE STEVEN, BARAL, DEBASIS, HERTE, LAWRENCE, LEE, HYUNG, JAI, VAN DE PITTE, STEVEN
Applicants: UNISYS CORP, UNISYS CORPORATION
Application year: 1987
Main classification: G11B5
IPC codes: G11B5