Magnetic recording tapes and devices

Abstract

A magnetic recording tape includes a tape substrate, a perpendicular magnetic recording layer disposed on the tape substrate, and a soft magnetic backing layer disposed between the recording layer and the tape substrate. The perpendicular magnetic recording layer includes magnetic particles suspended in an adhesive material, and the soft magnetic backing layer includes a continuous film of soft magnetic material. The magnetic particles in the recording layer include one of barium ferrite, strontium ferrite, epsilon iron oxide, and chromium dioxide. A tape storage device using such a tape is also provided. The device includes a read / write head having at least one probe write head for writing data to the magnetic tape by perpendicular recording, at least one reel of the magnetic tape described above, and a tape transport mechanism for transporting the magnetic tape past the read / write head.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE A magnetic recording tape having a perpendicular magnetic recording layer is described along with a method of making the tape and a storage device that uses the tape. [Background technology]

[0002] Conventional magnetic tape recording systems use tape media with a magnetic recording layer of barium ferrite particles applied by a liquid coating process, and a ring write head to record data on the layer. To increase the areal density of magnetic tape recording systems, it is important to increase the size / volume of the magnetic particles in the tape media. Reducing the size of the magnetic particles reduces the thermal stability of the written data over time. Therefore, to maintain data stability, the coercivity of the particles must be increased. Unfortunately, increasing the coercivity of the particles also increases the magnitude of the magnetic field required to change the magnetic state of the particles, i.e., to write data, and at a certain point, it becomes difficult to generate a sufficient magnetic field.

[0003] The hard disk drive (HDD) industry has been a pioneer in magnetic recording development due to the prevalence of hard disks in modern technology and the availability of huge budgets for research and development. Around 2005, the HDD industry commercialized a solution to the above problem, whereby the ring write head was replaced by a probe (single pole) write head combined with a sputtered disk media incorporating a soft magnetic underlayer. This marked a move from longitudinal recording, where the easy axis of magnetization in the recording layer is parallel to the disk surface, to perpendicular recording. For a perpendicular magnetic recording layer, the easy axis of magnetization is perpendicular to the plane of the disk, and the soft magnetic underlayer provides a return path for the magnetic flux from the write head. In this design, the recording medium is effectively present in the write gap of the head, i.e. the media becomes part of the write head, allowing for a stronger magnetic field in the area where data is written, thus resulting in a higher areal density.

[0004] Because the magnetic tape industry has smaller research budgets, the industry has traditionally followed developments in the HDD industry, and then adopted advances in HDD technology for magnetic tape. Thus, "Exploratory Experiments in Recording on Sputtered Magnetic Tape at an Areal Density of 148 Gb / in 2 ”, Tachibana et al., IEEE Transactions on Magnetics, Vol. 50, No. 11, pp. 1-6, November 2014, and “201 Gb / in 2The above breakthroughs were also applied to magnetic tape, as described in "Recording Areal Density on Sputtered Magnetic Tape", Furrer et al., IEEE Transactions on Magnetics, Vol. 54, No. 2, February 2018. These designs used sputtered media and materials such as platinum and ruthenium in the magnetic recording layer used for perpendicular recording in HDDs. Similarly, JP 2004-362746 and US 2007 / 0065682 describe perpendicular magnetic recording media having a particulate recording layer with a soft magnetic underlayer, where the magnetic grains in the recording layer are based on materials used in HDDs, specifically alloys of elements from groups 8-11 of the periodic table.

[0005] In view of the continuing need for advances in magnetic recording technology, improvements in magnetic tape media would be highly desirable. Summary of the Invention

[0006] A first aspect of the invention provides a magnetic recording tape comprising a tape substrate, a perpendicular magnetic recording layer disposed on the tape substrate, and a soft magnetic backing layer disposed between the recording layer and the tape substrate. The perpendicular magnetic recording layer includes magnetic particles suspended in an adhesive material, and the soft magnetic backing layer includes a continuous film of soft magnetic material. The magnetic particles in the recording layer include one of barium ferrite, strontium ferrite, epsilon iron oxide, and chromium dioxide.

[0007] The tape media embodying the present invention departs radically from the approach described above. The inventors have broken with the practice of following the lead from HDD technology and have moved away from the magnetic materials dictated by that technology for the recording layer used with the soft magnetic underlayer. Instead, the magnetic particle materials used in the embodiments of the present invention leverage those used in older particulate tape media. This is a radical move considering that the switch to media having a recording layer designed for use with a soft magnetic underlayer was made precisely to improve the performance of such previous materials. By overcoming the prejudice against what might otherwise be forgotten as a throwback to an older technology, the inventors have actually realized a particularly advantageous tape media. The combination of a perpendicular magnetic recording layer containing the magnetic particles described above (which is chemically very different from the Group 8-11 alloys of the prior art literature) with a continuous (i.e., not particulate) soft magnetic underlayer provides a magnetic tape that is easy to fabricate, inexpensive to make, and gives excellent areal density and overall performance. This is a significant advancement for magnetic tape storage.

[0008] The magnetic particles of the preferred embodiment comprise one of barium ferrite and strontium ferrite, most preferably strontium ferrite, which provides particularly high areal density recording.

[0009] The soft magnetic underlayer of the preferred embodiment may incorporate one or more antiferromagnetic or non-magnetic layers. For example, the soft magnetic underlayer may include two continuous soft magnetic material films with a very thin (less than 2 nm) antiferromagnetic coupling layer disposed between them, or may include a stack formed of multiple continuous soft magnetic material films with a non-magnetic separation layer disposed between them. These designs reduce noise in the readback process due to domain walls in the soft magnetic underlayer, improving the signal-to-noise ratio (SNR) during readback.

[0010] Preferred embodiments also include a capping layer formed on the soft magnetic underlayer. Such a capping layer may serve to protect the soft magnetic underlayer by inhibiting oxidation, or to adjust the electrical properties of the tape, or both. Advantageously, this capping layer may be formed in the same vacuum process as the underlayer itself.

[0011] In some embodiments, the magnetic particles may include at least one substitutional element to adjust the coercivity of the particles as further described below. Tapes embodying the invention may also include various additional layers, detailed below, to affect certain tape properties.

[0012] Another aspect of the present invention provides a tape storage device comprising a read / write head including at least one probe write head for writing data to a magnetic tape by perpendicular recording, at least one reel of magnetic tape according to the first aspect of the present invention described above, and a tape transport mechanism for transporting the magnetic tape past the read / write head.

[0013] A further aspect of the invention provides a method of making a magnetic recording tape according to the first aspect of the invention, in which a continuous film of soft magnetic material provided by a soft magnetic underlayer is made by one of a sputtering and evaporation process, and a perpendicular magnetic recording layer is formed on the underlayer by a liquid coating process.

[0014] Embodiments of the invention are described in more detail below, by way of illustrative and non-limiting examples, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram illustrating perpendicular recording in a magnetic tape-based storage device in accordance with at least one embodiment. [Diagram 2] FIG. 2 illustrates a portion of the component of FIG. 1 in accordance with at least one embodiment. [Diagram 3] 1 is a schematic cross-sectional view of a magnetic tape according to at least one embodiment. [Figure 4] 4 is a schematic cross-sectional view illustrating a modification to the magnetic tape of FIG. 3 according to at least one embodiment. [Diagram 5] 1 is a schematic cross-sectional view of a magnetic tape according to at least one embodiment. [Figure 6] 1 is a schematic cross-sectional view of a magnetic tape according to at least one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The schematic diagram of FIG. 1 illustrates the operation of a tape storage device embodying the present invention for perpendicular recording on magnetic tape. The device 1 has a read / write head including at least one probe write head 2 for writing data to a reel of magnetic tape 3. In practice, the read / write head of the device 1 may include one or more write modules, each including multiple probe write elements 2 for writing data in a respective track of the tape 3. For example, a typical read / write head may include two write modules, each having multiple (e.g., 32) write elements (and servo elements for tracking), and a read module having multiple read elements (not shown) for reading back data from the tape tracks. The tape reels are contained within cartridges / cassettes (not shown) that are mounted and presented to the head for read / write operations. The storage device 1 typically includes a library of tape cartridges that can be selected and automatically mounted into one or more drives, each drive including a read / write head as described above, as is well known in the art. During read / write operations, a tape transport mechanism, generally indicated at 5, operates to transport the tape 3 past the head in a commonly known manner.

[0017] The probe write head 2 comprises a single pole tip 6 and a return pole 7 for writing data to the tape 3 by perpendicular recording. The tape 3 comprises a tape substrate 9 and a perpendicular magnetic recording layer 10 disposed on the substrate 9. The recording layer 10 comprises magnetic particles suspended in an adhesive material, as will be further described below. The magnetic easy axes of the magnetic particles are oriented substantially perpendicular to the surface of the tape 3, as shown diagrammatically by the arrows on the magnetic particles 11 in this figure. The tape 3 further comprises a soft magnetic underlayer (SUL) 12 disposed between the recording layer 10 and the tape substrate 9. The SUL 12 comprises a continuous (non-particulate) film of soft magnetic material, as will be further described below.

[0018] In a write operation, magnetic flux from the probe tip 6 passes through the tape medium as shown diagrammatically by the arrows in this figure. The magnetic flux leaving the tip 6 is substantially perpendicular to the recording layer so that the grains are oriented to write a "1" or a "0" depending on the direction of the applied magnetic field. The SUL 12 provides a return path for the magnetic field to the return pole 7 of the write head.

[0019] 2 shows the main components of the recording system, drawn approximately to scale. In a preferred embodiment of the magnetic tape 3, the particulate recording layer 10 has a thickness t R 10 nm ≦ t R ≦70 nm, most preferably 10 nm≦t R The thickness of the SUL12, t S is preferably 20 nm≦t S ≦200 nm, most preferably 40 nm≦t S ≦120 nm. The tape substrate 9 is typically less than 5 microns thick and may be formed, for example, from PEN (polyethylene naphthalate), PET (polyethylene terephthalate), Spaltan substrate material, Aramid (aromatic polyamide), or PEEK (polyether ether ketone). Mixtures of these or other known materials or both may also be used in the substrate 9.

[0020] SUL12 is a composite material made of CoZrNb, FeAlSi, Fe 65 Co 35 , CoTaZr, FeCoTaZr, CoNiZr, Fe 44 Co 44 Zr7B4Cu, Ni 81 Fe 19 , Ni 45 Fe 55 , FeAlN, (Fe 70 Co 30 1. The SUL 12 includes at least one layer of soft magnetic material, such as SiO 2 , FeTaC, FeTaC, or other materials or combinations thereof. This soft magnetic layer is formed (directly or indirectly) on the substrate 9 by one of a sputtering and evaporation process, thereby creating a continuous (not particulate) thin film of soft magnetic material. Well-known sputtering / evaporation techniques can be applied to deposit the SUL 12, and specific examples are described in the Tachibana and Furrer references above. In general, the SUL can be deposited in one or more sputtering / evaporation stages and can have a composite structure, as described further below.

[0021] In the particulate magnetic recording layer 10, the magnetic particles include one of barium ferrite, strontium ferrite, epsilon iron oxide, and chromium dioxide. These particles are suspended in an adhesive material, typically some form of polymeric material. Examples of adhesive materials include hard resins using polyvinyl chloride-polyvinyl acetate-polyvinyl alcohol terpolymers. Such hard resins are bonded to a softer polyurethane (PU) resin component. Other examples of adhesive systems include sulfonated (PU) dispersion resins. Well-known techniques for particulate recording layers in magnetic tapes (see, for example, U.S. Pat. Nos. 9,478,331 and 9,378,878) can be used to fabricate the particulate magnetic layer. The magnetic particles in this layer are preferably monodisperse and have a substantially uniform size, i.e., the standard deviation of the particle volume is small, and preferably also the standard deviation of the coercivity is small. The recording layer 10 is formed (directly or indirectly) on the SUL 12 by a conventional liquid coating process. In this process, the tape is drawn past the extrusion head of a coating apparatus, depositing particulate material on the exposed surface of the tape. Perpendicular orientation of the grains in the magnetic layer can be achieved by applying a magnetic field to align the grains during the coating process. In some embodiments, the magnetic grains can include at least one substitution element to adjust the coercivity of the grains, for example, as described in the above-referenced U.S. patents. Examples of such substitution elements include Zn, Co, Al, Ti, Nb, and alloys of these elements and / or other elements such as Sn, Zr, and Mn. The magnetic recording layer of some embodiments can also include non-magnetic grains, for example grains of aluminum oxide, to control surface roughness and contact between the tape and the head, as is well known to those skilled in the art.

[0022] FIG. 3 is a schematic cross-sectional view of a preferred magnetic tape 20 embodying the present invention. The tape 20 includes a perpendicularly oriented fine-grained magnetic layer 21, the magnetic grains of which include one of barium ferrite and strontium ferrite, most preferably strontium ferrite. The recording layer 21 is formed on a composite SUL 22 including two successive soft magnetic material films 23a, 23b with a thin antiferromagnetic coupling layer 24 disposed therebetween. The antiferromagnetic coupling layer 24 has a thickness of less than 2 nm, preferably about 1 nm, and may be formed from an antiferromagnetic material such as Ru or IrMn. The soft magnetic layers 23a, 23b may be formed from the various materials mentioned above, each of which has a thickness of less than 100 nm. As a specific example, the SUL 22 may include 50 nm CoZrNb layers 23a, 23b and a 1 nm Ru coupling layer 24. Each of the constituent layers of SUL 22 are fabricated by one of the sputtering and evaporation processes, allowing all layers to be deposited in the same vacuum deposition procedure. The magnetic recording layer 21 is applied by the liquid coating process described above.

[0023] FIG. 4 shows a modification to the tape of FIG. 3, with like components indicated by the same reference numerals. This tape 25 includes a thin capping layer 26 formed on the SUL 22. This capping layer has a thickness of 1-5 nm and is deposited by evaporation / sputtering in the same vacuum deposition process as the SUL 22. The material of the capping layer 26 can be selected to protect the SUL 22 from oxidation or to adjust the electrical resistivity of the tape medium, or both. In particular, if the resistivity of the tape is too high, this can cause triboelectric charging and impair performance. The capping layer material can be selected to increase the electrical conductivity of the tape and thus inhibit triboelectric charging. Specific examples of capping layer materials include SiN and carbon-based films such as DLC (Diamond-Like Carbon).

[0024] FIG. 5 shows a schematic cross-sectional view of another preferred embodiment of a magnetic tape, where the above-mentioned components are again indicated by similar reference numerals. The tape 30 has a SUL 31 including a stack formed of a plurality of successive soft magnetic material films 32, with non-magnetic separation layers 33 disposed between the films 32. Although this example shows four soft magnetic layers 32, a multi-layer stack SUL can be formed with multiple layers 32 separated by non-magnetic separation layers 33. The layers 32, 33 can be formed from various materials as mentioned above. Here, in a particular embodiment, the SUL 31 can include multiple FeALSi layers 32, for example about 10 nm thick, with a carbon separation layer of about 4 nm located between the layers. Each of the constituent layers of the SUL 31 is made by one of the sputtering and evaporation processes, whereby all layers can be deposited in the same vacuum deposition procedure.

[0025] The magnetic recording tape described above, together with the sputtered / evaporated SUL and perpendicularly oriented particulate magnetic coating, allows for high density recording to be achieved using an easily fabricated and inexpensively made magnetic tape. Much higher areal densities can be achieved than tape media using conventional magnetic tapes and SULs as described in the Tachibana and Furrer references above. If desired, the use of expensive materials such as platinum and ruthenium can be eliminated entirely, or in embodiments, such materials can be utilized at cost-effective levels with respect to the thin Ru antiferromagnetic coupling layers of Figures 3 and 4. Thus, the overall cost of the tape media can be very significantly reduced. Furthermore, an added benefit of eliminating the ruthenium interlayer used in the Tachibana and Furrer tape media is that this reduces the distance between the magnetic recording layer and the SUL, further improving the write process and resulting in a higher SNR. The composite SUL structure of Figures 3-5 also reduces noise in the readback process due to the domain walls in the soft magnetic underlayer, further improving the SNR during readback.

[0026] The schematic diagram of FIG. 6 illustrates additional layers that may be included (individually or in combination) in a tape medium embodying the present invention. The tape 40 shown here has a liquid coated particulate magnetic layer 41 and a SUL 42 (which may have a composite layer structure as described above) along with a SUL capping layer 43. Disposed between the magnetic recording layer 41 and the SUL capping layer 43 is a non-magnetic layer 44. This non-magnetic layer 44 may be deposited by liquid coating prior to forming the recording layer and may be used to adjust the electrical conductivity of the tape surface or to adjust the surface roughness of the tape, or both. Exemplary materials for this layer 44 include polymeric materials containing carbon particles, with the amount of carbon being adjusted to adjust the electrical conductivity or the surface roughness, or both. Between the SUL 42 and the tape substrate 46, a thin seed layer 45, for example of Ta or Ti, is deposited by evaporation or sputtering. This seed layer may be used to increase adhesion or to affect the structure of the SUL, or both, for example to achieve a desired amorphous or polycrystalline SUL material structure. A backcoat layer 47 is also formed on the underside of the tape substrate 46, for example by a liquid coating process. The backcoat may be formed, for example, from a polymer containing carbon or other filler particles to adjust the roughness of the underside of the tape and to control adhesion during spooling and unspooling. The magnetic layer 41 and / or the non-magnetic backing layer 44 may also contain a lubricant (which may be mixed with the adhesive material or applied as a topcoat) to reduce friction between the tape and the read / write head. If additional layers 44, 45, and 47 are included in a tape embodying the invention, the thicknesses of these layers are preferably minimized as much as possible.

[0027] It will be understood that various other variations and modifications can be made to the particular embodiments described. Generally, where features are described herein with reference to a magnetic tape embodying the invention, corresponding features can be provided in the methods of making the magnetic recording tape and in the tape storage devices embodying the invention.

[0028] The description of various embodiments of the present invention is presented for the purpose of explanation and is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope of the described embodiments. The terminology used in this specification is selected to best explain the principles of the embodiments, practical applications, or technical improvements to the technology found in the market, or to enable those skilled in the art to understand the embodiments disclosed in this specification.

Claims

1. A tape substrate; a perpendicular magnetic recording layer disposed on the tape substrate, the perpendicular magnetic recording layer including magnetic particles suspended in an adhesive material; a soft magnetic underlayer including a continuous film of soft magnetic material and disposed between the recording layer and the tape substrate; A magnetic recording tape, wherein the magnetic particles include one of barium ferrite, strontium ferrite, epsilon iron oxide, and chromium dioxide.

2. 2. The magnetic tape of claim 1, wherein the magnetic particles comprise one of barium ferrite and strontium ferrite.

3. 2. The magnetic tape of claim 1, wherein the magnetic particles comprise strontium ferrite.

4. 2. The magnetic tape of claim 1, wherein the magnetic recording layer has a thickness of from 10 nm to 70 nm.

5. The magnetic tape of claim 1 , wherein the magnetic recording layer has a thickness of from 10 nm to 40 nm.

6. 2. The magnetic tape of claim 1, wherein the soft magnetic underlayer has a thickness of 20 nm to 200 nm.

7. 2. The magnetic tape of claim 1, wherein the soft magnetic underlayer has a thickness of 40 nm to 120 nm.

8. 2. The magnetic tape of claim 1, wherein the soft magnetic underlayer comprises two successive films of soft magnetic material with an antiferromagnetic coupling layer disposed between the films.

9. The magnetic tape of claim 8 wherein the antiferromagnetic coupling layer has a thickness of less than 2 nm.

10. 2. The magnetic tape of claim 1, wherein the soft magnetic underlayer comprises a laminate formed from a plurality of successive films of soft magnetic material with non-magnetic separation layers disposed between the films.

11. 11. The magnetic tape of claim 1, further comprising a capping layer formed on the soft magnetic underlayer.

12. The magnetic tape of claim 11, wherein the capping layer has a thickness of from 1 nm to 5 nm.

13. The magnetic tape of claim 1 , wherein the magnetic particles include at least one substitutional element for adjusting the coercivity of the particles.

14. 2. The magnetic tape of claim 1, wherein the magnetic particles are monodisperse.

15. 2. The magnetic tape of claim 1 including a nonmagnetic layer disposed between the magnetic recording layer and the soft magnetic underlayer.

16. The magnetic tape of claim 1 including a seedlayer disposed between the soft magnetic underlayer and the tape substrate.

17. 10. The magnetic tape of claim 1 including a backcoat layer formed on the lower surface of the tape substrate to adjust the roughness of the lower surface of the tape.

18. a read / write head including at least one probe write head for writing data to the magnetic tape by perpendicular recording; At least one reel of a magnetic tape according to any one of claims 1 to 17; a tape transport mechanism for transporting said magnetic tape past said read / write head.

19. 1. A method of making a magnetic recording tape, comprising: forming a soft magnetic underlayer on a tape substrate, the soft magnetic underlayer comprising a continuous film of soft magnetic material produced by one of a sputtering and evaporation process; forming a perpendicular magnetic recording layer comprising magnetic particles suspended in an adhesive material on the underlayer by a liquid coating process; The method, wherein the magnetic particles include one of barium ferrite, strontium ferrite, epsilon iron oxide, and chromium dioxide.

20. 20. The method of claim 19, wherein the magnetic particles comprise one of barium ferrite and strontium ferrite.

21. The method of claim 19 , wherein the magnetic particles comprise strontium ferrite.

22. 20. The method of claim 19, wherein the soft magnetic underlayer comprises two successive films of soft magnetic material with an antiferromagnetic coupling layer disposed between the films, and each of the successive films and the antiferromagnetic coupling layer is fabricated by one of a sputtering and evaporation process.

23. 20. The method of claim 19, wherein the soft magnetic underlayer is formed as a stack including a plurality of successive films of soft magnetic material with non-magnetic separation layers disposed between the films, and each of the successive films and the antiferromagnetic coupling layer is fabricated by one of a sputtering and evaporation process.

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