Patent Publication Number: US-2020279581-A1

Title: Magnetic recording medium and magnetic recording and reproducing device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-036145, filed Feb. 28, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a magnetic recording medium and a magnetic recording and reproducing device. 
     BACKGROUND 
     Magnetic recording media of HDDs entail a problem that a contaminant as cyclic siloxane, created by outgas, adheres to a surface of a medium to contaminate an element of a head, causing the occurrence of recording or reproduction errors. One of the examples of the pathways for entering of contaminant is a gap between plates of an outer circumferential portion of a cylinder in which a plurality of media are staked, via which a contaminant enters and attaches to the surface of a medium. To prevent this, there is a conventional attempt of reducing the possibility of contaminants attaching to media by placing activated carbon in the drive to adsorb the contaminants. However, lubricant is applied uniformly on the surfaces and the edge surfaces of the media, and therefore contaminants not adsorbed by activated carbon, in particular, those existing in the vicinities of the outer circumferences of the media, cannot be prevented actively from entering from the gap between the plates. For this reason, contaminants enter easily from the gap between the plates, significantly increasing the possibilities that contaminants attach on the large-area surfaces of the media. Thus, the frequency of occurrence of failure undesirably increases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a hard disk drive according to an embodiment. 
         FIG. 2  is a cross section schematically showing a structure of a magnetic recording medium according to the embodiment. 
         FIG. 3  is a decomposed perspective view showing the hard disk drive according to the embodiment. 
         FIG. 4  is a cross section of the HDD taken along line E-E in  FIG. 3 . 
         FIG. 5  is a cross section schematically showing a structure of a magnetic recording medium according to another embodiment. 
         FIG. 6  is a partially enlarged view schematically showing a part of  FIG. 5 . 
         FIG. 7  is a schematic diagram showing a removal system of lubrication application layer. 
         FIGS. 8A, 8B and 8C  are diagrams each illustrating a part of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a magnetic recording medium includes a recording area formed to carry out magnetic recording, and a non-recording area other than the recording area. The magnetic recording medium comprising a surface area including a pair of main surfaces and a side provided between the main surfaces, and a contaminant collecting portion provided in at least a part of the surface area within the non-recording area, and having a surface free energy higher than a surface free energy of the surface area within the recording area. 
     Magnetic recording media and magnetic recording and reproducing devices according to embodiments will now be described with reference to drawings. 
     What is disclosed in this specification is merely an example. Appropriate modifications which can be easily conceived by a person ordinarily skilled in the art without departing from the spirit of the embodiments naturally fall within the scope of the present invention. To further clarify explanation, for example, the width, thickness or shape of each structure may be schematically shown in the drawings compared with the actual forms. Note that the drawings are merely examples and do not limit the interpretation of the present invention. In the specification and drawings, elements which are identical to those of the already-mentioned figures are denoted by the same reference numbers. Thus, the detailed explanation of such elements may be omitted. 
     First Embodiment 
     As a magnetic recording and reproducing device, a hard disk drive (HDD) according to the first embodiment will now be described in detail. 
       FIG. 1  is a plan view of the HDD without its cover. 
     As shown in  FIG. 1 , the HDD comprises a rectangular housing  10 . The housing  10  comprises a rectangular box-shaped base  12  with an upper surface being opened, and a cover (top cover) which is not illustrated. The base  12  comprises a rectangular bottom wall  12   a  and side walls  12   b  provided to rise along peripheral edges of the bottom wall  12   a , which are all formed of, for example, aluminum, so to be integrated as one body. The cover can be formed, for example, from stainless steel into a rectangular plate shape, and can be screwed on the side wall  12   b  of the base  12  so as to airtightly block the upper surface opening of the base  12 . 
     As shown in  FIG. 1 , the housing  10  accommodates magnetic disks  18  as a disk-like magnetic recording media and a spindle motor  19  provided to support and rotate the magnetic disks  18 . The spindle motor  19  is disposed on the bottom wall  12   a . Each of the magnetic disks  18  comprises a substrate formed into, for example, a disk shape having a diameter of 95 mm (3.5 inches) of a nonmagnetic material, for example, glass, and a magnetic recording layer formed on an upper surface (first surface) of the substrate. The magnetic disk  18  is fit with a hub of the spindle motor  19  and further clamped with a clamp spring  20 . In this manner, the magnetic disks  18  are supported parallel to the bottom wall  12   a  of the base  12 . The magnetic disks  18  are rotated by the spindle motor  19  at a predetermined speed rate in a direction indicated by an arrow B. 
     The housing  10  accommodates therein a plurality of magnetic heads  17  which record and reproduce information on and from the magnetic disks  18 , and a head actuator assembly  22  which supports the magnetic heads  17  such that they are movable with respect to the magnetic disks  18 . Further, the housing  10  accommodates a voice coil motor (VCM)  24  which rotates and positions the actuator assembly  22 , a ramped loading mechanism  25  which holds the magnetic heads  17  at an unloading position spaced away from the magnetic disks  18  when the magnetic heads  17  are moved to the outermost circumference of the magnetic disks  18 , a board unit (FPC unit)  21  on which electronic components including a conversion connector are mounted, and a spoiler  70 . 
     A printed circuit board  27  is fixed by a screw to an outer surface of the bottom wall  12   a  of the base  12 . The printed circuit board constitutes a control unit which controls the operation of the spindle motor  19 , and also controls the operation of the VCM  24  and the magnetic heads  17  via the board unit  21 . 
       FIG. 2  is a cross section schematically showing a structure of the magnetic recording media used for the HDD according to the first embodiment. 
     As shown, this magnetic disk  18  comprises a substrate  1  and a multilayer  8  provided on the substrate  1 , and the multilayer  8  includes a magnetic recording layer  3 , a protective layer  4  provided on the magnetic recording layer  3 , and a lubricating layer  5  provided on the protective layer  4 . The magnetic recording medium  18  comprises surface regions including a pair of main surfaces  8   a  and  8   b  and a side surface  8   c  provided between the main surfaces  8   a  and  8   b . Further, the magnetic recording medium  18  comprises a recording area for carrying out magnetic recording and reproduction, and a non-recording area other than the recording area. Here, the side surface  8   c  in the non-recording area includes a portion where the protective layer  4  is exposed as a contaminant collecting portion  11 . 
     As the substrate  1 , a nonmagnetic substrate such as a glass substrate or an aluminum alloy substrate, can be employed. The aluminum alloy substrate used in this embodiment includes an aluminum plate and an alloy layer formed on the aluminum plate. For the protective layer  4 , diamond-like carbon (DLC) generated by chemical vapor deposition (CVD), for example, can be used. A usable example of the lubricating layer is perfluoropolyether. The surface free energy of the protective layer made of carbon is higher than the surface free energy of the lubricating layer made of perfluoropolyether. 
     According to the first embodiment, the surface free energy of the contaminant collecting portion  11  of the side surface  8   c  in the non-recording area is higher than the surface free energy of the lubricating layer of the recording area. With this configuration, contaminants such as outgas concentrate on the contaminant collecting portion  11 , to become easily attachable thereto. Thus, it is possible to inhibit contaminants from attaching to the lubricating layer surface in the recording area. 
     Second Embodiment 
     An HDD according to the second embodiment will now be described in detail. 
       FIG. 3  is an exploded perspective view of the HDD according to this embodiment, in which the cover thereof is removed. 
     As shown the HDD according to the second embodiment has a structure similar to that shown in  FIG. 1  except that a plurality of magnetic disks disposed to oppose each other are used as the magnetic disks  18 , and the HDD comprises, as actuator assembly  22 , a plurality of arms  17 , suspension assemblies (head gimbal assemblies, which may be referred to as HGA)  30  attached to the arms  32 , respectively, and magnetic heads  17  supported by the suspension assemblies  30 , respectively. 
     The magnetic disks each comprise a substrate of glass, and magnetic recording layers formed on an upper surface (first surface) and a lower surface (second surface) of the substrate. The magnetic disks  18  are fitted coaxially with each other on a hub), which will be described later) of the spindle motor  19 , and are clamped by a clamp spring  20 . The number of the arms  32  is greater by one than the number of the magnetic disks. Moreover, the number of the magnetic heads  17  is twice the number of the magnetic disks. 
       FIG. 4  is a cross section of the HDD taken along line E-E of  FIG. 3 . 
     In this example, the spindle motor  19  includes a shaft  60  provided to stand substantially up right on the bottom wall  12   a , a cylindrical pivot  62  rotatably supported around the shaft  60 , a substantially cylindrical hub  64  fixed around the pivot  62  coaxially, a stator coil SC fixed to the bottom wall  12   a  and disposed around the pivot  62 , and a cylindrical magnet M attached on an inner circumferential surface of the hub  64  so as to face the stator coil SC. The hub  64  comprises an outer circumferential surface located coaxial with the shaft  60  and an annular flange  65  formed in a lower end (on a bottom wall  12   a  side) of the outer circumferential surface so as to be integrated therewith. 
     The magnetic disks  18  are engaged with the outer circumferential surface of the hub  64  while the hub  64  inserted to inner holes thereof. Further, annular spacer rings  66  are each mounted around the outer circumferential surface of the hub  64  so as to be interposed between each respective adjacent pair of two magnetic disks  18 . The magnetic disks  18  and the spacer rings  66  are disposed on and above the flange  65  of the hub  64  in order, and are attached to the hub  64  while stacking one on another alternately. Here, the clamp spring  20  attached to the upper end of the hub  64  pressurizes the inner circumferential portions of the magnetic disks  18  and the spacer rings  66  to the flange  65  side, thus fixating the magnetic disks  18  in a stacked state while keeping predetermined intervals between each other. Thus, nine of the magnetic disks  18  are integrally supported by the pivot  62  and the hub  64  so as to be rotatable therewith. Further, the nine magnetic disks  18  are supported to be parallel to each other while keeping predetermined gap therebetween, and also substantially parallel to the bottom wall  12   a.    
     The housing  10  is formed to have a height (thickness) H of a maximum of 26.1 mm in accordance with the HDD standard. The magnetic disks  18  are each formed to have a thickness T of, for example, 0.635 mm and arranged to have a gap d between each adjacent pair of two magnetic disks  18 ), which is equivalent to the thickness of the spacer rings) of, for example, 1.58 mm. In this embodiment, a stack height h of all the magnetic disks (the height from the lower surface of the lowermost magnetic disk to the upper surface of the topmost magnetic disk) is set to 18.356 mm. 
     As shown, in each of the nine magnetic disks  18 , for example, when a region between X-X′ is formed as a recording area, an inner circumferential region with respect to X and an outer circumferential region with respect to X′ are non-recording areas. The contaminant collecting portion  11  can be formed in the non-recording areas. 
     Next, the structure of the magnetic recording media used for the HDD according to the second embodiment will be described with reference to  FIGS. 5 and 6 . 
       FIG. 5  shows the configuration of the outer circumferential edge surface of one of the magnetic disks  18  shown in  FIG. 4 . 
     As shown, this magnetic disk  18  includes a structure that the protective layer  4  and the lubricating layer  5  are stacked on each of both surfaces of the substrate  18 - 1  which includes magnetic recording layers, and comprises a pair of main surfaces  18   d  and  18   e , and a side surface  18   a  formed between the main surfaces  18   d  and  18   e . Further, a chamfered portion  18   c  is formed between the main surface  18   d  and the side surface  18   a , and a chamfered portion  18   b  is formed between the side surface  18   a  and the main surface  18   e . Further, a lubricating layer  5  is formed on each of the main surfaces  18   d  and  18   e , and the side surface  18   a  and the chamfered portions  18   b  and  18   c  are formed as a portion where the protective layer  4  is exposed from the lubricating layer  5 , which is the contaminant collecting portion  11 . 
       FIG. 6  is a partially enlarged diagram schematically showing the configuration of a region surrounded by a dotted line  110  in  FIG. 5 . 
     As shown, the magnetic recording medium  18  includes a substrate  1 , and a multilayer  8 ′ provided on the substrate  1  and containing a magnetic recording layer  3 . The substrate  1  comprises a main surface  1   d , another main surface (not shown) opposing the main surface  1   d , and an edge surface of the substrate  1 . The edge surface further comprises a side surface (not shown) formed between the main surfaces, a chamfered portion  1   a  provided between the main surface  1   d  and the side surface and another chamfered portion provided between the main surface and the side surface. 
     As in the case of the substrate used in the first embodiment, the substrate  1  can be formed from a nonmagnetic substrate such as a glass substrate or an aluminum alloy substrate. 
     The multilayer  8 ′ includes a soft magnetic underlying layer  6 , a seed layer  2  and an intermediate layer  9  stacked in order on the substrate  1 , and a magnetic recording layer  3  provided on the intermediate layer  9 . 
     A usable example of the material for the soft magnetic underlying layer (SUL)  6  is an amorphous alloy containing at least one selected from Fe, Co and Ta as main ingredients and an additional ingredient selected from Zr, B and Si, and FeCoTa is used here. 
     As the seed layer  2 , Ni, W and the like can be used, and NiW is used here. 
     As the intermediate layer (IL)  9 , a Ru alloy can be used. Cr or the like can be added to the Ru alloy in consideration of matching with the grid of the in-plane direction. Here, RuCr is used. 
     On the intermediate layer  9 , the magnetic recording layer (Mag)  3  can be formed. As the magnetic recording layer, a continuation film and a granular film containing, for example, CoPt as the main ingredients can be used. Here, CoPtCr is used. 
     For the manufacture of the magnetic disk  18  of such a structure, first, a nonmagnetic substrate such as of glass is prepared, and washed with pure water, followed by drying. Thereafter, the substrate is accommodated in a film-forming chamber of a DC magnetron sputtering device. Then, the film-forming chamber is evacuated. While maintaining a fixed degree of vacuum, Ar gas is introduced at a predetermined gas-pressure for each of the soft magnetic underlying layer  6 , the seed layer  2 , the intermediate layer  9 , and the magnetic recording layer  3  to form them in the order. 
     After forming the magnetic recording layer  3 , a C-protective layer  4  is formed by generating diamond-like carbon (DLC), for example, by the chemical vapor deposition (CVD) method. 
     Subsequently, the lubricating layer  5  is formed as follows. 
     After the step described above, a lubricant coating layer is formed on the DLC surface by performing, for example, dip coat with a lubricant on the surface of the protective layer  4 . Here, the lubricant coating layer is formed from a bond lubricating layer adsorbed on the surface of the protective layer  4 , and a free lubricating layer provided on the bond lubricating layer, but not adsorbed on the surface of the protective layer  4 . 
     Next, the bond lubricating layer and free lubricating layer of the lubricant coating layer on the side surface and the chamfered portion of a substrate  18 - 2  on which the lubricant coating layer is provided, are removed with a vanishing tape containing abrasives to expose the protective layer, and thus, the contaminant collecting portion  11  is obtained. 
       FIG. 7  is a schematic diagram showing a removal system  104  for the lubricant coating layer. 
     Further, each of  FIGS. 8A, 8B and 8C  illustrates a part of  FIG. 7 . 
     As shown, the lubricant-coating-layer removal system  140  includes three abrasive-containing vanishing tapes  131 ,  132  and  133 , pressurization members  135 ,  136  and  137  contactable on the vanishing tapes  131 ,  132  and  133 , respectively, and a driver (not shown) which rotate the substrate  18 - 2  in a direction indicated by an arrow  130 . 
       FIGS. 8A, 8B and 8C  are schematic diagrams each showing arrangement of the vanishing tapes  131 ,  132  or  133  and the substrate  18 - 2 . As shown in  FIG. 8A , the vanishing tape  131  is disposed to be contactable on a side surface  18   a ′ of the substrate  18 - 2  by the pressurization member  134 . As shown in  FIG. 8B , the vanishing tape  132  is disposed to be contactable on a first chamfered portion  18   b ′ of the substrate  18 - 2  by the pressurization member  135 . As shown in  FIG. 8C , the vanishing tape  133  is disposed to be contactable on a second chamfered portion  18   c ′ of the substrate  18 - 2  by the pressurization member  136 . 
     The lubricant-coating-layer removal system  140  operates as follows. That is, while rotating the substrate  18 - 2  in the direction of the arrow  130 , the abrasive-containing vanishing tapes  131 ,  132  and  133  are pressed against the side surface  18   a ′, the first chamfered portion  18   b ′ and the second chamfered portion  18   c ′, respectively, at a constant pressure by the pressurization members  134 ,  135  and  136 . Thus, the bond lubricating layer and the free lubricating layer of the lubricant coating layer can be removed to expose the protective layer on the side surface  18   a ′, the first chamfered portion  18   b ′ and the second chamfered portion  18   c ′, and thus the contaminant collecting portion can be prepared. 
     In this magnetic disk  18 , the protective layers of all of the side surface  18   a ′, the first chamfered portion  18   b ′ and the second chamfered portion  18   c ′ are exposed, but it suffices if the protective layer of at least one of the side surface  18   a ′, the first chamfered portion  18   b ′ and the second chamfered portion  18   c ′ is exposed. Moreover, the protective layer of the side surface  18   a ′, the first chamfered portion  18   b ′ or the second chamfered portion  18   c ′ may not necessarily be entirely exposed, but it suffices if it is partially exposed. 
     The rest of the lubricant coating layer of the magnetic disk provided with the contaminant collecting portion can be hardened by heating it for 1 hour at 150° C. with a heater. 
     The thus obtained magnetic recording medium can be used for at least one of the nine magnetic disks  18  of the disk device. With this structure, contaminants can be attached intensively in the contaminant collecting portion provided on the side surface  18   a ′, the first chamfered portion  18   b ′ and the second chamfered portion  18   c ′, located on a side surface  18   a ′ side of the housing, and thus it is possible to reduce the rate of contaminants entering between a plurality of magnetic disks  18 . In terms of suppressing the contamination entering between disks, it is effective when the magnetic disk provided the contaminant collecting portion is used for at least the second disk from the cover side to the eighth disk of the nine magnetic disks, and it is also possible to use it for all the magnetic disks. 
     Measurement of Surface Free Energy 
     The surface free energy of each of the lubricating layer  5  and the protective layer  4  was measured as follows. 
     A magnetic recording medium  18 - 3  comprising a lubricating layer on an outermost surface was formed in a similar manner to that of the magnetic recording medium shown in  FIG. 6  except that the lubricant coating layer was not removed. 
     1 μl of a droplet the surface free energy of which is known was dropped on the medium and an angle between the medium and the droplet was measured with a contact angle meter. A similar measurement was carried out four times on within the medium surface. Using the formula of Young-Dupre, the surface free energy of the medium was calculated and the result was 26.0 mN/m. On the other hand, a magnetic recording medium  18 - 4  with a protective layer on an outermost surface was formed similarly except that the lubricant was not applied. The thus obtained medium was subjected to the contact angle measurement, and the surface free energy was 50.5 mN/m. Thus, it was found that the surface free energy is higher in this medium as compared with the medium with the lubricant applied on the outermost surface. 
     Evaluation of Attachment of Contaminant on Protective Layer and Lubricating Layer 
     The magnetic recording medium  18 - 3  with lubricant on the outermost surface was mounted in an HDD, and the drive was operated under an environment of 80° C. for 260 hours. Here, gas was generated from inside the HDD, and attached on the medium. 
     As the contaminant attachment evaluation, the amount of Si+ ion was measured with ToF-SIMS, and the result indicated the count was 500. 
     On the other hand, the magnetic recording medium  18 - 4  with the C-protective layer on the outermost surface without applying a lubricant was mounted in an HDD and a similar measurement was carried out. The count of Si+ ions was 2200, and thus the result indicated contaminants attach more easily than in the case of the magnetic recording medium  18 - 3 . 
     As described above, it is understood that the surface free energy is higher in the protective layer than in the lubricating layer, and contaminants attach more easily. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.