US20140363700A1 - Magnetic recording medium - Google Patents

Magnetic recording medium Download PDF

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Publication number
US20140363700A1
US20140363700A1 US14/289,762 US201414289762A US2014363700A1 US 20140363700 A1 US20140363700 A1 US 20140363700A1 US 201414289762 A US201414289762 A US 201414289762A US 2014363700 A1 US2014363700 A1 US 2014363700A1
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Prior art keywords
layer
magnetic recording
recording medium
magnetic
indicates
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Inventor
Junichi Tachibana
Noboru Sekiguchi
Tomoe Ozaki
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Sony Corp
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Sony Corp
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Assigned to SONY CORPORATION reassignment SONY CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: OZAKI, TOMOE, TACHIBANA, JUNICHI, SEKIGUCHI, NOBORU
Publication of US20140363700A1 publication Critical patent/US20140363700A1/en
Priority to US15/208,932 priority Critical patent/US10424329B2/en
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73923—Organic polymer substrates
    • G11B5/73927—Polyester substrates, e.g. polyethylene terephthalate
    • G11B5/732—
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/64—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent
    • G11B5/65—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent characterised by its composition
    • G11B5/658—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent characterised by its composition containing oxygen, e.g. molecular oxygen or magnetic oxide
    • G11B5/7325—
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/7368—Non-polymeric layer under the lowermost magnetic recording layer
    • G11B5/7379—Seed layer, e.g. at least one non-magnetic layer is specifically adapted as a seed or seeding layer
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73923—Organic polymer substrates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/74—Record carriers characterised by the form, e.g. sheet shaped to wrap around a drum
    • G11B5/78—Tape carriers

Definitions

  • the present technology relates to a magnetic recording medium.
  • the present technology relates to a magnetic recording medium including a seed layer.
  • a magnetic recording medium in which a film of a CoCrPt-based metal material having a high magnetic anisotropy is formed on a flexible substrate, for example, by a sputtering method, and in addition, this material is crystallized and oriented in a direction perpendicular to the surface of the substrate.
  • this magnetic recording medium it has been desired to improve the magnetic characteristics by improvement of the orientation of a magnetic recording layer, and hence, various techniques to satisfy this desire have been studied in recent years. For example, according to Japanese Unexamined Patent Application Publication No.
  • a magnetic recording medium in which an amorphous layer, a seed layer, an under layer, a magnetic layer, and a protective layer are at least sequentially laminated on a substrate.
  • the seed layer is formed from one of Ti, Cr, Mo, W, Zr, a Ti alloy, a Cr alloy, and a Zr alloy
  • the under layer is formed from Ru
  • the magnetic layer is formed to have a granular structure.
  • a magnetic recording medium which includes a substrate, a seed layer, an under layer, and a perpendicular recording layer having a granular structure and in which (Ms ⁇ 1.5 (1 ⁇ Rs) 0.33 ), Ms, and ⁇ satisfy the following relations.
  • Ms indicates a saturated magnetization amount
  • ⁇ indicates the gradient of a M-H loop around a coercive force Hc
  • ⁇ indicates the thickness of the perpendicular recording layer
  • Rs indicates a squareness ratio
  • a magnetic recording medium having an excellent SNR can be provided.
  • FIG. 1 is a schematic cross-sectional view showing one example of the structure of a magnetic recording medium according to an embodiment of the present technology.
  • FIG. 2 is a schematic view showing one example of the structure of a sputtering apparatus used for manufacturing a magnetic recording medium according to an embodiment of the present technology.
  • FIG. 3 is a schematic cross-sectional view showing one modified example of the structure of a magnetic recording medium according to an embodiment of the present technology.
  • a seed layer, an under layer, and a recording layer may have either a single-layer structure or a multilayer structure.
  • a layer having a multilayer structure is preferably employed.
  • a double-layer structure is preferably employed.
  • FIG. 1 is a cross-sectional view schematically showing one example of the structure of a magnetic recording medium according to an embodiment of the present technology.
  • the magnetic recording medium according to this embodiment is a so-called single-layer perpendicular magnetic recording medium, and as shown in FIG. 1 , this magnetic recording medium includes a substrate 11 , a seed layer 12 provided on the surface of the substrate 11 , an under layer 13 provided on the surface of the seed layer 12 , a magnetic recording layer 14 provided on the surface of the under layer 13 , a protective layer 15 provided on the surface of the magnetic recording layer 14 , and a top coat layer 16 provided on the surface of the protective layer 15 .
  • the magnetic recording medium of this embodiment is a magnetic recording medium which can record an information signal by a ring type head or the like.
  • a magnetic recording medium having no soft magnetic lining layer is called a “single-layer perpendicular magnetic recording medium”, and a magnetic recording medium having a soft magnetic lining layer is called a “double-layer perpendicular magnetic recording medium”.
  • This magnetic recording medium is suitably used as a data archive-purpose storage medium which is expected to be increasingly in demand from now on.
  • This magnetic recording medium is able to realize 10 times or more the surface recording density of a current storage-purpose coating type magnetic recording medium, that is, to realize a surface recording density of 50 Gb/in 2 .
  • a common linear recording type data cartridge is formed using a magnetic recording medium having the surface recording density as described above, a large capacity recording of 50 TB or more per one data cartridge can be realized.
  • Ms indicates a saturated magnetization amount
  • ⁇ indicates the gradient of a M-H loop around a coercive force Hc
  • ⁇ indicates the thickness of the perpendicular recording layer 14
  • Rs indicates a squareness ratio
  • the formula F(Ms, ⁇ , ⁇ , Rs), the saturated magnetization amount Ms, and the gradient ⁇ of a M-H loop around a coercive force Sc satisfy the following relations. When those relations are satisfied, a magnetic recording medium having an excellent SNR can be realized.
  • the value of the formula F mainly relates to a noise output.
  • a signal output primarily depends on low spacing and reproducing head sensitivity, and as medium characteristics, low noise characteristics are desired.
  • the formula F(Ms, ⁇ , ⁇ , Rs) is set to satisfy F(Ms, ⁇ , ⁇ , Rs) ⁇ 0.1 [ ⁇ emu ⁇ (mm) ⁇ 1.5 ], so that the low noise characteristics of the magnetic recording medium are realized.
  • the value of the formula F is preferably decreased as described above so as to realize the low noise characteristics, when the value of the saturated magnetization amount Ms is excessively decreased, a decrease in signal output becomes larger than a decrease in noise output, and as a result, the SNR is also decreased.
  • the formula F is first set to satisfy F ⁇ 0.1 [ ⁇ emu ⁇ (mm) ⁇ 1.5 ], and the saturated magnetization amount Ms is further set to satisfy Ms ⁇ 450 [emu/cc].
  • the gradient ⁇ of a M-H loop around a coercive force Hc is a parameter correlating to exchange interactions between magnetic grains. Accordingly, when ⁇ is decreased, since the exchange interactions are decreased, the activation volume, which indicates a volume in the state in which crystalline grains are bonded together by the exchange interactions and magnetic interactions, is decreased, and as a result, the noise is reduced. However, when ⁇ is excessively decreased, a large head magnetic field is necessary for saturation recording, and in addition, the magnetization reversal becomes slow; hence, the signal output is decreased, and as a result, the SNR is decreased. Hence, in this embodiment, the gradient ⁇ is set to satisfy ⁇ 1.2.
  • the formula F(Ms, ⁇ , ⁇ , Rs), the saturated magnetization amount Ms, and the gradient of ⁇ of a M-H loop around a coercive force Hc satisfy the above relations
  • the formula f(Ku, V, T) preferably further satisfies the following relation.
  • f(Ku, V, t) is set to satisfy f(Ku, V, T) ⁇ 65.
  • the size of magnetic grains is preferably decreased in order to realize the reduction in noise, when the size of the magnetic grains is decreased, the influence of thermal disturbance is increased, and as a result, the magnetic state may not be maintained in some cases.
  • Ku ⁇ V/k B ⁇ T is preferably set to satisfy Ku ⁇ V/k B ⁇ T ⁇ 60 to 80.
  • Ku ⁇ V/k B ⁇ T is preferably set to satisfy Ku ⁇ V/k B ⁇ T ⁇ 65.
  • the substrate 11 used as a support is, for example, a long film.
  • a flexible non-magnetic substrate is preferably used.
  • a material of the non-magnetic substrate for example, a flexible high molecular weight material which is commonly used for magnetic recording media may be used.
  • the high molecular weight material as described above for example, there may be mentioned a polyester, a polyolefin, a cellulose derivative, a vinyl-based resin, a polyimide, a polyamide, and a polycarbonate.
  • the seed layer 12 is provided between the substrate 11 and the under layer 13 .
  • the seed layer 12 preferably has an amorphous state and preferably contains a metal having a melting point of 2,000° C. or less.
  • the seed layer 12 may further contain O (oxygen) besides the metal having a melting point of 2,000° C. or less. This oxygen is a very small amount of impurity oxygen trapped in the seed layer 12 when the seed layer 12 is formed, for example, by a sputtering method.
  • the “seed layer” does not indicate an intermediate layer which has a crystalline structure similar to that of the under layer 13 and which is provided for crystalline growth but indicates an intermediate layer which improves the perpendicular orientation of the under layer 13 by the flatness and the amorphous state of the seed layer 12 .
  • the “alloy” indicates, for example, at least one of a solid solution, a eutectic compound, and an intermetallic compound, each of which contains Ti and Cr.
  • the “amorphous state” indicates a state in which a halo pattern is observed by an electron diffraction method, and in which the crystalline structure is difficult to be identified.
  • the seed layer 12 having an amorphous state and containing a metal having a melting point of 2,000° C. or less not only has a function to suppress the influence of an O 2 gas and H 2 O adsorbed on and in the substrate 11 but also has a function to improve the perpendicular orientation of the under layer 13 by forming a metal flat surface on the surface of the substrate 11 .
  • the seed layer 12 is placed in a crystalline state, columnar shapes are clearly formed in association with the crystalline growth, and irregularities of the surface of the substrate 11 are apparently increased. As a result, the crystalline orientation of the under layer 13 is degraded.
  • the metal having a melting point of 2,000° C. or less may be either a metal element or an alloy.
  • the metal having a melting point of 2,000° C. or less for example, at least one element selected from the group consisting of Ti, Cr, Co, Ni, Al, and the like may be mentioned.
  • an alloy containing Ti and Cr, an alloy containing Ni and Al, an alloy containing Co and Cr, a Ti element, and the like may be mentioned, and among those mentioned above, an alloy containing Ti and Cr is particularly preferable.
  • one purpose of providing the seed layer 12 is to realize the flatness of the substrate surface.
  • a metal having a low melting point is used as a material of the seed layer 12 , or in more particular, when a metal having a melting point of 2,000° C. or less is used, it is estimated that a preferable flat surface can be formed.
  • the correlation between the melting point and the diffusion coefficient of a material has been commonly understood, and when the material has a lower melting point, the diffusion coefficient thereof is increased.
  • the diffusion coefficient of a material has a significant influence on the film growth mechanism, and as the diffusion coefficient is increased, migration on the surface of the substrate 11 is increased; hence, it is believed that the density is increased, and that the flatness of the surface is improved.
  • the rate of O with respect to the total amount of Ti, Cr, and O contained in the seed layer 12 is preferably 15 atomic % (at %) or less and more preferably 10 at % or less.
  • the rate of oxygen is more than 15 at %, since a TiO 2 crystal is generated, crystalline nuclear formation of the under layer 13 formed on the surface of the seed layer 12 is influenced thereby, and the orientation of the under layer 13 is remarkably degraded.
  • the rate of Ti with respect to the total amount of Ti and Cr contained in the seed layer 12 is preferably 30 to 100 at % and more preferably 50 to 100 at %.
  • the rate of Ti is less than 30 at %, the (100) plane of a body-centered cubic lattice (bcc) structure of Cr is oriented, and the orientation of the under layer 13 formed on the surface of the seed layer 12 is degraded.
  • the rate of the above element can be obtained as described below.
  • analysis of the outermost surface of the etched seed layer 12 is performed by an Auger electron spectroscopy, and the rate of the average atomic number with respect to the thickness is regarded as the rate of the element.
  • analysis is performed on three elements, Ti, Cr, and O, and the element content represented by a percentage rate is identified.
  • the alloy may also contain at least one metal element as an additive element besides Ti and Cr.
  • a metal element having a melting point of 2,000° C. or less is preferable, and for example, at least one element selected from the group consisting of Co, Ni, Al, and the like may be mentioned.
  • the under layer 13 preferably has a crystalline structure similar to that of the magnetic recording layer 14 .
  • the under layer 13 preferably contains a material having a hexagonal close-packed (hcp) structure similar to that of the Co-based alloy, and the c axis of this structure is preferably oriented in a direction perpendicular to the film surface (that is, in a film thickness direction).
  • hcp hexagonal close-packed
  • a material containing Ru is preferably used, and in particular, a Ru element or a Ru alloy is preferable.
  • a Ru alloy oxide such as Ru—SiC 2 , Ru—TiC 2 , Ru—ZrO 2 , or the like may be mentioned.
  • the magnetic recording layer 14 is preferably a perpendicular recording layer which contains a Co-based alloy and has a granular structure.
  • This granular magnetic layer is formed of ferromagnetic crystalline grains containing a Co-based alloy and non-magnetic grain boundaries (non-magnetic material) surrounding the ferromagnetic crystalline grains.
  • this granular magnetic layer is formed of columns (columnar crystals) containing a Co-based alloy and non-magnetic grain boundaries (oxides such as SiC 2 ) which surround those columns and magnetically separate the columns from each other.
  • the magnetic recording layer can be formed so that the columns are magnetically separated from each other.
  • the Co-based alloy has a hexagonal close-packed (hop) structure, and the c axis thereof is oriented in a perpendicular direction (film thickness direction) to the film surface.
  • a CoCrPt-based alloy containing at least Co, Cr, and Pt is preferably used.
  • the CoCrPt-based alloy is not particularly limited, and the CoCrPt-based alloy may further contain at least one additive element.
  • the additive element for example, at least one element selected from the group consisting of Ni, Ta, and the like may be mentioned.
  • the non-magnetic grain boundary surrounding the ferromagnetic crystalline grain contains a non-magnetic metal material.
  • the metal includes a half metal.
  • the non-magnetic metal material for example, either a metal oxide or a metal nitride may be used, and in order to more stably maintain the granular structure, a metal oxide is preferably used.
  • a metal oxide containing at least one element selected from the group consisting of Si, Cr, Co, Al, Ti, Ta, Zr, Ce, Y, and Hf may be mentioned, and a metal oxide containing at least a Si oxide (that is, SiO 2 ) is preferable.
  • the metal oxide for example, SiO 2 , Cr 2 O 3 , CoO, Al 2 O 3 , TiO 2 , Ta 2 O 5 , ZrO 2 , or HfO 2 may be mentioned.
  • the metal nitride for example, a metal nitride containing at least one element selected from the group consisting of Si, Cr, Co, Al, Ti, Ta, Zr, Ce, and Hf may be mentioned.
  • the metal nitride for example, SiN, TiN, and AlN may be mentioned.
  • the non-magnetic grain boundary preferably contains the metal oxide.
  • the CoCrPt-based alloy contained in the ferromagnetic crystalline grain and the Si oxide contained in the non-magnetic grain boundary preferably have an average composition represented by the following formula (1).
  • the reason for this is that since a saturated magnetization amount Ms can be realized which suppresses the influence of a demagnetizing field and which can secure a sufficient reproduction output, a high SNR can be secured.
  • the above composition may be obtained as described below.
  • analysis by an Auger electron spectroscopy is performed on the outermost surface of the magnetic recording layer 14 thus etched, and the rate of the average atomic number with respect to the thickness is regarded as the rate of the element.
  • the analysis is performed on five elements, Co, Pt, Cr, Si, and O, and the element content represented by a percentage rate is identified.
  • the magnetic recording medium according to this embodiment is a single-layer magnetic recording medium having no lining layer (soft magnetic lining layer) containing a soft magnetic material
  • this type of magnetic recording medium when the influence of the demagnetizing field caused by the magnetic recording layer 14 is large in a perpendicular direction, sufficient recording in a perpendicular direction tends to be difficult to perform.
  • the demagnetizing field is increased in proportion to the saturated magnetization amount Ms of the magnetic recording layer 14 , in order to suppress the demagnetizing field, the saturated magnetization amount Ms is preferably decreased. However, when the saturated magnetization amount Ms is decreased, a residual magnetization amount Mr is decreased, and as a result, a reproduction output is decreased.
  • a material contained in the magnetic recording layer 14 is preferably selected so that the influence of the demagnetizing field can be suppressed (that is, the saturated magnetization amount Ms is decreased), and at the same time, a residual magnetization amount Mr which can secure a sufficient reproduction output can be obtained.
  • the average composition represented by the above formula (1) those characteristics can both be satisfied, and hence, a high SNR can be secured.
  • the protective layer 15 contains, for example, a carbon material or silicon dioxide (SiC 2 ), and in view of the film strength of the protective layer 15 , a carbon material is preferably contained.
  • a carbon material for example, there may be mentioned graphite, diamond-like carbon (DLC), diamond, or the like.
  • the top coat layer 16 contains, for example, a lubricant agent.
  • a lubricant agent for example, a silicone lubricant agent, a hydrocarbon lubricant agent, a fluorinated hydrocarbon lubricant agent, or the like may be used.
  • FIG. 2 is a schematic view showing one example of the structure of a sputtering apparatus used for manufacturing a magnetic recording medium according to an embodiment of the present technology.
  • This sputtering apparatus is a continuous winding type sputtering apparatus used for film formation of the seed layer 12 , the under layer 13 , and magnetic recording layer 14 , and as shown in FIG. 2 , the sputtering apparatus includes a film formation chamber 21 , a drum 22 , cathodes 23 a to 23 c , a feeding reel 24 , and a winding reel 25 .
  • the sputtering apparatus is, for example, a DC (direct current) magnetron sputtering type apparatus, the sputtering method is not limited to this method.
  • the film formation chamber 21 is connected to a vacuum pump (not shown) via an exhaust port 26 , and by this vacuum pump, the atmosphere inside the film formation chamber 21 is set to a predetermined degree of vacuum.
  • a vacuum pump not shown
  • the rotatable drum 22 , the feeding reel 24 , and the winding reel 25 are disposed.
  • the substrate 11 which is unwound out of the feeding reel 24 is wound by the winding reel 25 through the drum 22 .
  • the drum 22 is provided with a cooling mechanism (not shown) and is cooled, for example, to approximately ⁇ 20° C. in sputtering.
  • the cathodes 23 a to 23 c are disposed to face the cylindrical surface of the drum 22 .
  • Targets are set to the respective cathodes 23 a to 23 c .
  • the targets which form the seed layer 12 , the under layer 13 , and the magnetic recording layer 14 are set to the cathodes 23 a , 23 b , and 23 c , respectively.
  • cathodes 23 a to 23 c a plurality of types of films, that is, the seed layer 12 , the under layer 13 , and the magnetic recording layer 14 , are simultaneously formed.
  • the atmosphere of the film formation chamber 21 in sputtering is set, for example, to approximately 1 ⁇ 10 ⁇ 5 to 5 ⁇ 10 ⁇ 5 Pa.
  • the film thickness and the characteristics (such as magnetic characteristics) of each of the seed layer 12 , the under layer 13 , and the magnetic recording layer 14 may be controlled, for example, by adjusting a tape line speed for winding the substrate 11 , the pressure (sputtering gas pressure) of an Ar gas introduced in sputtering, and an input electric power.
  • the tape line speed is preferably in a range of approximately 1 to 10 m/min.
  • the sputtering gas pressure is preferably in a range of approximately 0.1 to 5 Pa.
  • the input electric power is preferably in a range of approximately 30 to 150 mW/cm 2 .
  • a magnetic recording medium according to an embodiment of the present technology may be formed, for example, as described below.
  • the seed layer 12 , the under layer 13 , and the magnetic recording layer 14 are formed on the substrate 11 .
  • the film formation is performed as described below.
  • the inside of the film formation chamber 21 is vacuumed to a predetermined pressure.
  • a process gas such as an Ar gas
  • the targets set to the cathodes 23 a to 23 c are sputtered, so that the seed layer 12 , the under layer 13 , and the magnetic recording layer 14 are sequentially formed on the surface of the substrate 11 .
  • the protective layer 15 is formed on the surface of the magnetic recording layer 14 .
  • a method for forming the protective layer 15 for example, a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method may be used.
  • CVD chemical vapor deposition
  • PVD physical vapor deposition
  • a lubricant agent is applied on the surface of the protective layer 15 to form the top coat layer 16 .
  • various application methods such as gravure coating and dip coating, may be used.
  • the magnetic recording medium has a laminate structure in which the seed layer 12 , the under layer 13 , and the magnetic recording layer (perpendicular recording layer) 14 having a granular structure are laminated in this order.
  • the formula F(Ms, ⁇ , ⁇ , Rs), the saturated magnetization amount Ms, and the gradient ⁇ of a M-H loop around a coercive force Hc satisfy the following relations. Hence, a magnetic recording medium having an excellent SNR can be realized.
  • the seed layer 12 which has an amorphous state and which contains a metal having a melting point of 2,000° C. or less is provided between the substrate 11 and the under layer 13 , the influence of a O 2 gas and/or H 2 O adsorbed on and in the substrate 11 on the under layer 13 is suppressed, and at the same time, the orientation of the under layer 13 and that of the magnetic recording layer 14 are improved by the metal flat surface formed on the surface of the substrate 11 , so that excellent magnetic characteristics can be achieved. Hence, improvement in medium performance, such as increase in output and reduction in noise, can be realized.
  • the seed layer 12 may be configured to have a double-layer structure in which a first seed layer (lower-side seed layer) 12 a and a second seed layer (upper-side seed layer) 12 b are provided.
  • the first seed layer 12 a is provided at a substrate 11 side
  • the second seed layer 12 b is provided at an under layer 13 side.
  • the first seed layer 12 a may be formed from a material similar to that of the seed layer 12 of the above embodiment.
  • the second seed layer 12 b contains, for example, a material having a composition different from that of the first seed layer 12 a .
  • the seed layer 12 is configured to have a double-layer structure as described above, the orientation of the under layer 13 and that of the magnetic recording layer 14 can be further improved, and hence, the magnetic characteristics can be further improved.
  • the seed layer 12 may be configured to have a multilayer structure having at least three layers.
  • the under layer 13 may be configured to have a double-layer structure in which a first under layer (lower-side under layer) 13 a and a second under layer (upper-side under layer) 13 b are provided.
  • the first under layer 13 a is provided at a seed layer 12 side
  • the second under layer 13 b is provided at a magnetic recording layer 14 side.
  • the thickness of the second under layer 13 b is preferably larger than that of the first under layer 13 a . The reason for this is that the characteristics of the magnetic recording medium can be improved.
  • the under layer 13 may be configured to have a multilayer structure having at least three layers.
  • the numerical range of the formula F(Ms, ⁇ , ⁇ , Rs) may only be set to satisfy F ⁇ 0.1 [ ⁇ emu ⁇ (mm) ⁇ 1.5 ].
  • the numerical range of the formula f(Ku, V, T) is also preferably set to satisfy f ⁇ 65.
  • the thickness of each layer laminated on the non-magnetic substrate was measured as described below. First, a magnetic tape was cut in a direction perpendicular to its primary surface, and the cross-section thereof is photographed by a transmission electron microscope (TEM). Next, from a TEM image thus photographed, the thickness of each layer was obtained.
  • TEM transmission electron microscope
  • a TiCr seed layer having a thickness of 5 nm was formed on a high molecular weight film functioning as the non-magnetic substrate.
  • TiCr target (however, a TiCr target used in Example 1-2 had a composition different from that of a TiCr target used in Examples 1-1 and 1-3 to 1-8, and Comparative Examples 1-1 to 1-4, and the composition of the TiCr seed layer was changed as shown in Table 1.)
  • the background pressure indicates a pressure immediately before sputtering is started.
  • a Ru under layer having a thickness of 20 nm was formed on the TiCr seed layer.
  • Gas pressure The gas pressure was changed as follows in accordance with each sample.
  • (CoCrPt)—(SiO 2 ) target (however, in order to form a magnetic recording layer having the composition shown in Table 1, the composition of the (CoCrPt)—(SiO 2 ) target was adjusted in accordance with each sample.
  • Gas species The gas species to be introduced was changed as follows in accordance with each sample.
  • a mixed gas containing Ar and O 2 (3%) was simultaneously introduced.
  • the gas flow rate of the mixed gas was set to 5 sccm.
  • Gas pressure The gas pressure was changed as follows in accordance with each sample.
  • a protective layer having a thickness of 5 nm was formed from carbon on the (CoCrPt)—(SiO 2 ) magnetic recording layer.
  • Target carbon target
  • a lubricant agent was applied on the protective layer to form the top coat layer on the protective layer.
  • the film formation conditions for the step of forming a seed layer were changed as follows.
  • the gas pressure of the film formation conditions for the magnetic recording layer was changed to 1.5 Pa.
  • a magnetic tape was obtained in a manner similar to that in Example 1-4 except for the changes described above.
  • Target The material of the target was changed in Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-5 so as to form a seed layer containing the material shown in Table 3.
  • Example 1-1 Except that the film formation conditions for the step of forming a magnetic recording layer were changed as follows, a magnetic tape was obtained in a manner similar to that in Example 1-1.
  • Gas species The gas species to be introduced was changed as follows in accordance with each sample.
  • Example 3-4 a mixed gas containing Ar and O 2 (3%) was simultaneously introduced.
  • the gas flow rate of the mixed gas was set to 2.6 sccm
  • Example 3-5 the gas flow rate of the mixed gas was set to 4.0 sccm.
  • a TiCr seed layer having a thickness of 10 nm was formed on a high molecular weight film functioning as the non-magnetic substrate.
  • a NiW seed layer having a thickness of 5 nm was formed on the TiCr seed layer.
  • a Ru under layer having a thickness of 5 nm was formed on the NiW seed layer.
  • a Ru under layer having a thickness of 25 nm was formed on the Ru under layer functioning as the first under layer.
  • first and the second under layers were both formed from Ru, since the film formation condition (gas pressure) was changed therebetween, the properties of the films were different from each other.
  • Gas species Besides an Ar gas, a mixed gas containing Ar and O 2 (3%) was simultaneously introduced. In addition, the gas flow rate of the mixed gas was set to 2.6 sccm.
  • the state and the crystalline structure of the under layer were analyzed by examination of the ⁇ /2 ⁇ characteristics using an x-ray diffraction apparatus.
  • the state and the crystalline structure of the seed layer were analyzed.
  • dots are obtained as an electron diffraction image
  • rings are obtained as an electron diffraction image
  • a halo is obtained as an electron diffraction image.
  • the composition of the seed layer was analyzed as described below. After the sample was etched from a surface layer thereof with ion beams, the analysis was performed on the outermost surface thus etched by an Auger electron spectroscopy, and the rate of the average atomic number with respect to the thickness was regarded as the rate of the element. In particular, the analysis was performed on three elements, Ti, Cr, and O, and the element content represented by a percentage rate was identified.
  • the auger electron spectroscopy is an analytical method in which by irradiation of a solid surface with narrower electron beams, the energy and the number of generated Auger electrons are measured, so that the type and the quantity of an element present on the solid surface are identified.
  • the energy of an Auger electron thus emitted depends on energy emitted when an electron drops from an outer-shell level to the empty level formed by electron beams irradiated on the surface and has an intrinsic value determined by the element; hence, the element present on the sample surface can be identified.
  • composition of the magnetic recording layer was analyzed as described below. As in the case of the above “(c) composition of seed layer”, analysis by an Auger electron spectroscopy was performed, and the rate of the average atomic number with respect to the thickness was regarded as the rate of the element. In particular, the analysis was performed on five elements, Co, Pt, Cr, Si, and O, and the element content represented by a percentage rate was identified.
  • the magnetic characteristics of the magnetic recording layer were evaluated as described below. First, by the use of a vibrating sample magnetometer (VSM), the M-H loop of the magnetic recording layer was obtained. Next, from the M-H loop thus obtained, the saturated magnetization amount Ms, the squareness ratio Rs, the coercive force Hc, and the gradient ⁇ of the M-H loop around the coercive force Hc were obtained. In addition, the measurement was performed in a direction perpendicular to the sample surface, and a so-called demagnetizing field correction by 47 ⁇ Ms based on the sample shape was not performed.
  • VSM vibrating sample magnetometer
  • the heat stability of the magnetic tape was evaluated as described below. First, the magnetic anisotropic energy Ku, the activation volume V, and the absolute temperature T were obtained as described below.
  • the absolute temperature T was regarded as 293K (environment at a room temperature of 20° C.)
  • the recording/reproducing characteristics were evaluated as described below. First, by the use of a ring type recording head and a giant magnetoresistive (GMR) type reproducing head, recording/reproducing were performed by reciprocating vibration of the head using a piezoelectric stage, that is, measurement was performed by a so-called drag tester. In this measurement, a read track width of the reproducing head was set to 120 nm. Next, a recording wavelength was set to 250 kilo flux changes per inch (kFCI), and the SNR was obtained by calculation using the ratio between a peak-to-peak voltage of a reproduced waveform and a voltage obtained from an integrated value of a noise spectrum from 0 to 500 kFCI.
  • GMR giant magnetoresistive
  • a minimum SNR necessary to operate a recording/reproducing system is approximately 16 dB. Since the digital SNR is lower than the SNR measured by this measurement method (the above measurement method used for evaluation of recording/reproducing characteristics) by approximately 4 dB, in order to secure a digital SNR of 16 dB, the SNR measured by this measurement method is necessary to be approximately 20 dB. Hence, it is concluded that the SNR by this measurement method is necessary to be at least 20 dB.
  • a SNR margin is preferably further included in consideration of degradation in practical characteristics, such as decrease in output and deformation of the magnetic tape, generated by sliding between the magnetic tape and the magnetic head.
  • the SNR is preferably set to 23 dB or more.
  • Table 1 shows the film formation conditions and the layer structure of the magnetic tape of each of Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-4.
  • Table 2 shows the evaluation results of the magnetic tape of each of Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-4.
  • Table 3 shows the film formation conditions and the layer structure of Examples 2-1 to 2-8.
  • Table 4 shows the evaluation results of the magnetic tape of each of Examples 2-1 to 2-8.
  • Example 2-1 3500 0.65
  • Example 2-2 3500 0.6
  • Example 2-3 3000
  • Example 2-4 3500 0.65
  • Example 2-5 3500 0.63
  • Example 2-6 4500 0.85
  • Example 2-7 4000 0.82
  • Example 2-8 3800 0.78
  • Table 5 shows the film formation conditions and the layer structure of the magnetic tape of each of Examples 3-1 to 3-5.
  • Example 3-1 1.5 Ar 0 63 14.5 12.5 12 10
  • Example 3-2 1.5 Ar 0 63 14.5 12.5 12 15
  • Example 3-3 1.5 Ar 0 58.5 13.5 18 10
  • Example 3-4 1.5 Ar, 2.6 69 13.8 9.2 8 20 Ar + O 2
  • Example 3-5 1.5 Ar, 4.0 69 13.8 9.2 8 20 Ar + O 2
  • Amp Amorphous Background pressure: 1.0 ⁇ 10 ⁇ 5 [Pa] (for the seed layer, the under layer, and the magnetic recording layer) Seed layer: melting point of Ti/1,666° C., melting point of Cr/1,857° C.
  • Table 6 shows the evaluation results of the magnetic tape of each of Examples 3-1 to 3-5.
  • Tables 7 and 8 show the film formation conditions and the layer structure of the magnetic tape of Example 4.
  • Table 9 shows the evaluation results of the magnetic tape of Example 4.
  • the saturated magnetization amount Ms, and the gradient ⁇ of a M-H loop around a coercive force Hc satisfy F(Ms, ⁇ , ⁇ , Rs) ⁇ 0.1 [ ⁇ emu ⁇ (mm) ⁇ 1.5 ], Ms ⁇ 450 [emu/cc], and ⁇ 1.2, the SNR can be set to 20 dB or more.
  • the saturated magnetization amount Ms, and the gradient ⁇ of a M-H loop around a coercive force Hc satisfy the above relations, and in addition, when the formula f(Ku, V, k B ) is also set to satisfy f(Ku, V, k B ) ⁇ 65, the output attenuation can be set to 1.0 dB or less.
  • the expression of the above effect is not limited to the case in which a TiCr alloy is used as the material of the seed layer.
  • a metal having a melting point of 2,000° C. or less is used as the material of the seed layer, and in addition, when F, Ms, and ⁇ or F, Ms, ⁇ and f satisfy the above relations, it is believed that an effect similar to that described above can be obtained.
  • the metal having a melting point of 2,000° C. or less for example, besides a TiCr alloy, a Ti element, a NiAl alloy, or a CoCr alloy may also be used.
  • the structure, the method, the step, the shape, the material, the numeral, and the like described in the above embodiments are merely shown by way of example, and if necessary, different structure, method, step, shape, material, numeral, and the like may also be used.
  • a magnetic recording medium includes: a substrate; a seed layer; an under layer; and a perpendicular recording layer having a granular structure, and (Ms ⁇ 1.5 (1 ⁇ Rs) 0.33 ), Ms, and ⁇ satisfy the following relations.
  • Ms indicates a saturated magnetization amount
  • ⁇ indicates the gradient of a M-H loop around a coercive force Hc
  • ⁇ indicates the thickness of the perpendicular recording layer
  • Rs indicates a squareness ratio.
  • the under layer includes Ru.
  • the perpendicular recording layer has a granular structure in which grains containing Co, Pt, and Cr are separated from each other with oxides provided therebetween.
  • the perpendicular recording layer has an average composition represented by the following formula (1).
  • the substrate is a flexible non-magnetic substrate.

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