The present invention relates to data storage systems, and more particularly, this invention relates to magnetic recording media having a surface recording density of 1 terabit or more per square inch.
The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. Accordingly, an important and ongoing goal involves increasing the amount of information able to be stored in the limited area and volume of HDDs. Increasing the areal recording density of HDDs provides one technical approach to achieve this goal. In particular, reducing the size of recording bits and components associated therewith offers an effective means to increase areal recording density. However, the continual push to miniaturize the recording bits and associated components presents its own set of challenges and obstacles. For instance, as the size of the ferromagnetic crystal grains in a magnetic recording layer become smaller and smaller, the crystal grains may become thermally unstable, such that thermal fluctuations result in magnetization reversal and the loss of recorded data. Increasing the magnetic anisotropy of the magnetic particles may improve the thermal stability thereof; however, an increase in the magnetic anisotropy requires an increase in the switching field needed to switch the magnetization of the magnetic particles during a write operation.
According to one embodiment, a perpendicular magnetic recording medium includes: a substrate; an underlayer positioned above the substrate; and a magnetic recording layer structure positioned above the underlayer, where the magnetic recording layer structure includes at least a first magnetic recording layer and a second magnetic recording layer, the second magnetic layer being positioned above first magnetic recording layer, where the first magnetic recording layer includes a first segregant material positioned between magnetic grains thereof, the first segregant material being primarily boron nitride (BN), and where the second magnetic recording layer includes a second segregant material positioned between the magnetic grains thereof, the second segregant material being primarily an oxide.
According to another embodiment, a perpendicular magnetic recording medium includes: a substrate; and a magnetic recording layer structure positioned above the substrate, the magnetic recording layer structure including: a first magnetic recording layer having a first segregant material positioned between magnetic grains thereof; and a second magnetic recording layer positioned above first magnetic recording layer, the second magnetic recording layer having a second segregant material positioned between the magnetic grains thereof, where the magnetic grains of the first and second magnetic recording layers include a L10 type FePt ordered alloy, and where at least the second segregant has a thermal conductivity that is less than FePt.
Any of these embodiments may be implemented in a magnetic data storage system such as a disk drive system, which may include a magnetic head, a drive mechanism for passing a magnetic medium (e.g., hard disk) over the magnetic head, and a controller electrically coupled to the magnetic head.
Other aspects and advantages of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.
For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings.
The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.
Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.
It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified.
As also used herein, the term “about” denotes an interval of accuracy that ensures the technical effect of the feature in question. In various approaches, the term “about” when combined with a value, refers to plus and minus 10% of the reference value. For example, a thickness of about 10 nm refers to a thickness of 10 nm±1 nm.
The following description discloses several preferred embodiments of magnetic storage systems and/or related systems and methods, as well as operation and/or component parts thereof.
Efforts are continually made to increase the areal recording density of magnetic media. Areal density, e.g., as measured in bits per square inch, may be defined as the product of the track density (the tracks per inch radially on the magnetic medium, such as a disk) and the linear density (the bits per inch along each track). For a disk, the bits are written closely-spaced to form circular tracks on the disk surface, where each of the bits may comprise an ensemble of magnetic grains.
An important factor relevant to track density is the magnetic write width (MWW). The magnetic write width determines the width of a magnetic bit recorded by the write/main pole of the write head. Thus, the smaller the magnetic write width, the greater the number of tracks of data that can be written to the media. Stated another way, high track density is associated with a narrow magnetic write width.
Moreover, an important factor relevant to linear density is the signal to noise ratio (SNR). Typically, a higher signal to noise ratio corresponds to a higher readable linear density. One approach to increase the signal to noise ratio involves reducing the size of the magnetic grains included within a magnetic recording layer. However, reducing the size of the magnetic grains may affect their thermal stability, which is given by: KuV/kbT, where Ku denotes the magnetocrystalline anisotropy, V is the average grain volume, kb denotes the Boltzmann constant, and T denotes the temperature. Preferably, KuV/kbT>˜60 to avoid thermal decay. Accordingly, to compensate for the reduction in volume, V, of the magnetic nanoparticles, the magnetic anisotropy (Ku) of the magnetic nanoparticles may be increased to maintain thermal stability. However, increasing the magnetic anisotropy also increases the coercivity of the ferromagnetic recording material, which may exceed the switching field (i.e., the write field) capability of the write head.
Heat assisted magnetic recording (HAMR), also referred to as thermally assisted magnetic recording, has emerged as a promising magnetic recording technique to address the difficulty in maintaining both the thermal stability and write-ability of the magnetic media. As the coercivity of the ferromagnetic recording material is temperature dependent, HAMR employs heat to lower the effective coercivity of a localized region of the magnetic media and write data therein. The data state becomes stored, or “fixed,” upon cooling the magnetic media to ambient temperatures (i.e., normal operating temperatures typically in a range between about 15° C. and 60° C.). HAMR thus allows use of ferromagnetic recording materials with substantially higher magnetic anisotropy and smaller thermally stable grains as compared to conventional magnetic recording techniques.
As discussed previously, achieving a higher surface recording density in a magnetic recording medium while maintaining thermal stability requires a magnetic recording layer having high perpendicular magnetic anisotropic energy, Ku. CoCr-based and CoCrPt-based alloys have been employed as magnetic recording layer material. However, CoCr- and CoCrPt-based alloys do not possess a magnetic anisotropic constant that is suitable (e.g. high enough) to achieve surface recording densities exceeding 1 Tbit/inch2. Accordingly, to satisfy the continued push to increase the recording density of a magnetic recording medium, materials with higher magnetic anisotropic constants than a Co—Cr-based alloy must be employed.
An L10 type FePt ordered alloy is a material that has higher perpendicular magnetic recording anisotropic energy Ku than current CoCrPt-based alloys, and has thus attracted attention as a material for next-generation magnetic recording layers. Such an ordered alloy has a structure in which the different atoms therein are arranged in a regular/ordered fashion (e.g., there is a regular/ordered arrangement of the atoms among the atomic sites in the crystal lattice of the alloy). L10 type FePt ordered alloys have been described, for example, in Nature photonics, Vol. 3, No. 4, pp. 189-190, April 2009, “Data Storage: Heat-assisted Magnetic Recording”.
Exchange interaction between crystal lattices must be reduced to use this L10 type FePt ordered alloy as a magnetic recording layer. One approach to reduce this exchange interaction involves granulating the L10 type FePt ordered alloy, whereby a nonmagnetic material such as SiO2 or C is added to the alloy. An example of this approach is disclosed in Japanese Unexamined Patent Publication No. 2008-91024. A granulated L10 type FePt ordered alloy comprises magnetic crystal grains comprising primarily FePt, which are surrounded by crystal grain boundaries of a nonmagnetic material such that the magnetic crystal grains are magnetically divided.
Generally, using an FePt alloy having an L10 type crystal structure for a magnetic recording layer requires that the FePt layer take on a (001) orientation. It is known in the art that ordering FePt to form a (001) orientation requires heating the FePt alloy to 300° C. or higher prior to, during and/or after film formation. One example of such a heating process is disclosed in Japanese Unexamined Patent Document No. 2012-048784. It is also known in the art that the (001) orientation of a FePt alloy may be formed by using a suitable material for an underlayer that is positioned underneath the FePt layer. For instance, use of an MgO underlayer results in the FePt layer having a (001) orientation, as discussed in IEEE Transactions on Magnetics, Vol. 42, No. 10, October 2006, pp. 3017-3019, “Interfacial Effects of MgO Buffer Layer on Perpendicular Anisotropy of L10 FePt films”.
The high recording anisotropic energy Ku of an L10 type FePt ordered alloy makes it particularly useful as a magnetic recording material for HAMR. Thermal management is an important factor in HAMR recording. For example, while a magnetic medium needs to be heated to high temperatures (e.g. at least 100K above the Curie temperature) during the writing process, the medium also needs to be cooled quickly in order to avoid thermal destabilization of the written information. Conventional heat sink layers are thus typically used in a HAMR medium to conduct or direct heat away from the recording layer after writing in order to limit thermal erasure, and thus obtain a high SNR and narrow recording width. Such heat sink layers are preferably positioned underneath the orientation controlling underlayer (e.g., the MgO underlayer noted above). Additionally, such heat sink layers may generally have a crystallographic orientation substantially aligned with that of the underlayer, as well as a greater thermal conductivity than said underlayer. However, conventional heat sink layers may conduct heat both vertically and laterally, thereby resulting in possible lateral thermal spreading during the writing process, which may limit track density and the size of the data bits. Indeed, the use of conventional heat sink layers is often insufficient to form ultra-micro recording bits, there the recording width and recording length approaches 100 nm and 50 nm, respectively.
Furthermore, the use of conventional non-magnetic materials such as SiO2 or C to granulate the L10 type FePt ordered alloy may also contribute to unwanted lateral thermal spreading, as these non-magnetic materials have a greater thermal conductivity than FePt and tend to transmit heat in the in-plane direction during the writing process. Moreover, the use of SiO2 as the non-magnetic material often leads to poor grain separation in the L10 type FePt ordered alloy. Moreover still, the use of C as the non-magnetic material generally results in the formation of spherical FePt magnetic grains, which undesirably limits the achievable thickness of the media for a given average grain diameter, thereby imposing a serious limitation on the signal strength of the media.
Embodiments described herein overcome the aforementioned drawbacks by providing a magnetic recording medium including at least the following layers positioned above a substrate in the following order: a buffer layer, an underlayer, and a multilayer recording layer. In some approaches, the buffer layer may have an amorphous structure. In other approaches, the buffer layer may have a body centered cubic (bcc) crystal structure. In additional approaches, the multilayer recording layer may comprise at least two granulated recording layers each of which have a L10 type crystal structure. In preferred approaches, the granulated recording layer positioned closest to the substrate includes a BN segregant, and the granulated recording layer positioned farthest from the substrate includes an oxide segregant. As discussed in detail below, the structure and composition of the multilayer recording layers disclosed herein promote good grain separation, low surface roughness and minimal heat transmittance in the in-plane direction during recording, thus enabling high density recording.
Following are several examples of general and specific embodiments relating to the use, manufacture, structure, properties, etc. of the novel magnetic media disclosed herein.
In one general embodiment, a perpendicular magnetic recording medium includes: a substrate; an underlayer positioned above the substrate; and a magnetic recording layer structure positioned above the underlayer, where the magnetic recording layer structure includes at least a first magnetic recording layer and a second magnetic recording layer, the second magnetic layer being positioned above first magnetic recording layer, where the first magnetic recording layer includes a first segregant material positioned between magnetic grains thereof, the first segregant material being primarily boron nitride (BN), and where the second magnetic recording layer includes a second segregant material positioned between the magnetic grains thereof, the second segregant material being primarily an oxide.
In another general embodiment, a perpendicular magnetic recording medium includes: a substrate; and a magnetic recording layer structure positioned above the substrate, the magnetic recording layer structure including: a first magnetic recording layer having a first segregant material positioned between magnetic grains thereof; and a second magnetic recording layer positioned above first magnetic recording layer, the second magnetic recording layer having a second segregant material positioned between the magnetic grains thereof, where the magnetic grains of the first and second magnetic recording layers include a L10 type FePt ordered alloy, and where at least the second segregant has a thermal conductivity that is less than FePt.
Referring now to
As shown in
At least one slider 113 is positioned near the disk 112, each slider 113 supporting one or more magnetic read/write portions 121, e.g., of a magnetic head according to any of the approaches described and/or suggested herein. As the disk rotates, slider 113 is moved radially in and out over disk surface 122 so that portions 121 may access different tracks of the disk where desired data are recorded and/or to be written. Each slider 113 is attached to an actuator arm 119 by means of a suspension 115. The suspension 115 provides a slight spring force which biases slider 113 against the disk surface 122. Each actuator arm 119 is attached to an actuator 127. The actuator 127 as shown in
During operation of the disk storage system, the rotation of disk 112 generates an air bearing between slider 113 and disk surface 122 which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension 115 and supports slider 113 off and slightly above the disk surface by a small, substantially constant spacing during normal operation. Note that in some embodiments, the slider 113 may slide along the disk surface 122.
The various components of the disk storage system are controlled in operation by control signals generated by controller 129, such as access control signals and internal clock signals. Typically, control unit 129 comprises logic control circuits, storage (e.g., memory), and a microprocessor. In a preferred approach, the control unit 129 is electrically coupled (e.g., via wire, cable, line, etc.) to the one or more magnetic read/write portions 121, for controlling operation thereof. The control unit 129 generates control signals to control various system operations such as drive motor control signals on line 123 and head position and seek control signals on line 128. The control signals on line 128 provide the desired current profiles to optimally move and position slider 113 to the desired data track on disk 112. Read and write signals are communicated to and from read/write portions 121 by way of recording channel 125.
The above description of a typical magnetic disk storage system, and the accompanying illustration of
An interface may also be provided for communication between the disk drive and a host (integral or external) to send and receive the data and for controlling the operation of the disk drive and communicating the status of the disk drive to the host, all as will be understood by those of skill in the art.
In a typical head, an inductive write portion includes a coil layer embedded in one or more insulation layers (insulation stack), the insulation stack being located between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write portion. The pole piece layers may be connected at a back gap. Currents are conducted through the coil layer, which produce magnetic fields in the pole pieces. The magnetic fields fringe across the gap at the ABS for the purpose of writing bits of magnetic field information in tracks on moving media, such as in circular tracks on a rotating magnetic disk.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the magnetic field produced to write information on the recording medium.
As shown in the magnetic head 200 of
Perpendicular writing is achieved by forcing flux through the stitch pole 208 into the main pole 206 and then to the surface of the disk positioned towards the ABS 218.
In various optional approaches, the magnetic head 200 may be configured for heat assisted magnetic recording (HAMR). Accordingly, for HAMR operation, the magnetic head 200 may include a heating mechanism of any known type to heat the magnetic medium (not shown). For instance, as shown in
An optional heater is shown in
Moreover, in various optional approaches, the piggyback magnetic head 201 may also be configured for heat assisted magnetic recording (HAMR). Thus, for HAMR operation, the magnetic head 200 may additionally include a light source 230 (e.g., a laser) that illuminates a near field transducer 232 of known type via a waveguide 234.
Referring now to
As shown in
Layer 310 may be comprised of a suitable light transmitting material, as would be known by one of reasonable skill in the relevant art. Exemplary materials include Ta2O5, and/or TiO2. As shown, the core layer 310 has approximately uniform cross section along its length. As well known in the art, the optical waveguide can have a number of other possible designs including a planar solid immersion mirror or planar solid immersion lens which have a non-uniform core cross section along the waveguide's length.
In various approaches, coil layers (not shown) and various insulating and spacer layers (not shown) might reside in the cavity bounded by the ABS, back-gap(s) 304, lower return pole 302, and/or upper bounding layers 306, 308, and 312 as would be recognized by those of skill in the art. Layers 302, 304, 306, and 308 may be comprised of a suitable magnetic alloy or material, as would be known by one of reasonable skill in the relevant art. Exemplary materials include Co, Fe, Ni, Cr and combinations thereof.
As described above,
With continued reference to
In various optional approaches, the recording/playback head 406 may additionally be configured for heat assisted magnetic recording (HAMR). Accordingly, for HAMR operation, the recording/playback head 406 may include a heating mechanism of any known type to heat, and thus lower the effective coercivity, of a localized region on the magnetic medium 400 surface in the vicinity of the main pole 410. For instance, as shown in
Improvements in longitudinal recording media have been limited due to issues associated with thermal stability and recording field strength. Accordingly, pursuant to the current push to increase the areal recording density of recording media, perpendicular recording media (PMR) has been developed and found to be superior to longitudinal recording media.
The orientation of magnetic impulses in the magnetic recording layer 506 is substantially perpendicular to the surface of the recording layer. The magnetization of the soft underlayer 504 is oriented in (or parallel to) the plane of the soft underlayer 504. As particularly shown in
As noted above, the magnetization of the soft underlayer 504 is oriented in (parallel to) the plane of the soft underlayer 504, and may represented by an arrow extending into the paper. However, as shown in
It should be again noted that in various approaches, the perpendicular head 508 may be configured for heat assisted magnetic recording (HAMR). Accordingly, for HAMR operation, the perpendicular head 508 may include a heating mechanism of any known type to heat, and thus lower the effective coercivity of, a localized region on the magnetic media surface in the vicinity of the main pole 518. For instance, as shown in
Except as otherwise described herein with reference to the various inventive embodiments, the various components of the structures of
Referring now to
As shown in the embodiment depicted in
As also shown in
In other approaches, the buffer layer structure 604 may include at least one buffer layer configured to function as a heat sink layer, i.e., configured to conduct or direct heat away from the magnetic recording layer structure 608 during a write operation. In various approaches, this heat sink layer buffer may include a material having a high thermal conductivity (e.g., greater than 30 W/m-K, preferably greater than 100 W/m-K), which may be particularly useful for HAMR. In preferred approaches, this heat sink buffer layer may preferably have a higher thermal conductivity than the underlayer 606. In further approaches, the heat sink buffer layer may have a body centered cubic (bcc) structure and a crystallographic orientation that is substantially aligned with the crystallographic orientation of the underlayer 606. In such approaches, the crystallographic orientations of both the heat sink buffer layer and the underlayer 606 may be aligned substantially along the substrate normal (i.e., an axis perpendicular the upper surface of the substrate, as indicated by dotted arrow in
In yet more approaches, the buffer layer structure 604 may include at least one amorphous buffer layer and at least one heat sink buffer layer.
In additional approaches, the buffer layer structure 604 may include a plurality of buffer layers, where at least one, some, the majority, or all of said buffer layers are amorphous. In alternative approaches, the buffer layer structure 604 may include a plurality of buffer layers, where at least one, some, the majority, or all of said buffer layers are heat sink layers.
Referring again to the magnetic recording medium 600 shown in
In some approaches, the underlayer 606 may include MgO. In approaches where the underlayer 606 includes MgO, the Mg content may be in range between about 40 at % to about 55 at %, and the O content may be in a range between about 40 at % to about 55 at %. Comparable orientation controlling characteristics may be obtained in approaches where impurities are present in an MgO underlayer, provided the impurities are present in an amount of 10 at % or less.
In other approaches, the orientation controlling intermediate underlayer 606 may include one or more cubic crystal compounds including but not limited to SrTiO3, indium tin oxide (ITO), MnO, TiN, RuAl, etc., and/or alloys thereof. In more approaches, the orientation controlling intermediate layer 606 may include one or more body-centered cubic structure metals including but not limited to Cr, Mo, W, etc., and/or alloys thereof. In yet more approaches, the orientation controlling intermediate layer 606 may include one or more face-centered cubic structure metals including but not limited to Pt, Pd, Ni, Au, Ag, Cu, etc., and/or alloys thereof. In further approaches, these materials suitable for use in the orientation controlling intermediate layer 606 may be combined in plurality to form a laminated-type orientation controlling intermediate layer 606.
While not shown in
With continued reference to
In preferred approaches, the magnetic grains 610 in each of the first and second magnetic recording layers 608A, 608B may include a L10 type FePt ordered alloy. In more approaches, the magnetic grains 610 in each of the first and second magnetic recording layers 608A, 608B may include a L10 type FePtX ordered alloy, where X may include one or more of: Ag, Cu, Au, Ni, Mn, etc. In yet more approaches, the one or more additional materials in the L10 type FePtX ordered alloy of the first recording layer 608A may be the same or different from the one or more additional materials in the L10 type FePtX ordered alloy of the second magnetic recording layer 608B.
As also shown in
As additionally shown in
In approaches where the magnetic grains 610 of the first and second magnetic recording layers 608A, 608B include at least a L10 type FePt ordered alloy, the first segregant 612 and/or the second segregant 614 may include one or more materials having a thermal conductivity that is lower than the thermal conductivity of FePt. In some approaches, an amount (in vol %) of the second segregant 614 in the second magnetic recording layer 608B is greater than an amount (in vol %) of the first segregant 612 in the first magnetic recording layer 608A.
In further approaches, the total thickness, t, of the magnetic recording layer structure 608 may be in a range between about 4 to about 20 nm, but could be higher or lower depending on the desired embodiment. In preferred approaches, the total thickness, t, of the magnetic recording layer structure 608 may be in a range between about 8 to about 15 nm. In additional approaches, the thickness, tA, of the first magnetic recording layer 608A may be about 20% to about 80% of the total thickness, t, of the magnetic recording layer structure 608.
As shown in
Although not shown in
Regardless of how many magnetic recording layers are included in the magnetic recording layer structure 608, preferably all of the magnetic recording layers may have a similar magnetic grain pitch, p. The magnetic grain pitch may be due to the conformal growth on the lowermost magnetic layer that is transferred to the magnetic layers formed there above.
Moreover, the first and second magnetic recording layers 608A, 608B may be formed via a sputtering process. According to one particular approach, the magnetic grain material(s) and one or more segregant component(s) of the first magnetic recording material 608A may be sputtered from the same target; however, in another approach, the magnetic grain material(s) and/or segregant component(s) of the first magnetic recording material 608A may be sputtered from their respective targets. Likewise, the magnetic grain material(s) and one or more segregant component(s) of the second magnetic recording material 608B may be sputtered from the same target in one approach or be sputtered from their respective targets in another approach.
In preferred approaches, the magnetic grain and segregant materials of the first magnetic recording layer 608A are deposited onto the magnetic recording medium 600 at the same time. In similar preferred approaches, the magnetic grain and segregant materials of the second magnetic recording layer 608B are deposited onto the magnetic recording medium 600 at the same time. Additionally, said deposition preferably occurs in a heated environment, e.g., from about 400° C. to about 800° C., in approaches where the first and/or second magnetic recording layers 608A, 608B include a L10 type FePt ordered alloy. The FePt-segregant systems in the first and/or second magnetic recording layers 608A, 608B self-assemble to form isolated magnetic grains surrounded by segregant material located along the grain boundaries, as magnetic and segregant materials do not form a solid solution even at high temperature. Thus, the first and/or second magnetic recording layers 608A, 608B have an alternating FePt/segregant/FePt/segregant, etc., configuration in the in-plane direction (i.e., the lateral direction), and an uninterrupted FePt magnetic grain configuration extending in the vertical direction of the magnetic recording structure 608 (i.e., extending throughout the total thickness of the magnetic recording structure 608). As a result, the thermal conductivity of the first and/or second magnetic recording layers 608A, 608B in the lateral direction may be reduced due to the presence of multiple FePt/segregant interfaces, and is typically about 5-20 times smaller than in the thermal conductivity associated with the vertical direction.
In yet further approaches, the first and second magnetic recording layers 608A, 608B may be patterned magnetic recording layers. In patterned recording media, the ensemble of ferromagnetic grains that form a bit are replaced with a single isolated magnetic region, or island, that may be purposefully placed in a location where the write transducer expects to find the bit in order to write information and where the readback transducer expects to detect the information stored thereto. To reduce the magnetic moment between the isolated magnetic regions or islands in order to form the pattern, magnetic material is destroyed, removed or its magnetic moment substantially reduced or eliminated, leaving nonmagnetic regions therebetween. There are two types of patterned magnetic recording media: discrete track media (DTM) and bit patterned media (BPM). For DTM, the isolated magnetic regions form concentric data tracks of magnetic material, where the data tracks are radially separated from one another by concentric grooves of nonmagnetic material. In BPM, the isolated magnetic regions form individual bits or data islands which are isolated from one another by non-magnetic material/crystal grain boundaries (e.g. a segregant). Each bit or data island in BPM includes a single magnetic domain, which may be comprised of a single magnetic grain or a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume.
While not shown in
Again with reference to
A lubricant layer 620 may also be positioned above the protective overcoat layer 618, as shown in
The formation of the magnetic recording media 600, 601, 603, 605 shown in
Illustrative Embodiments and Comparative Examples
The following illustrative embodiments describe the novel magnetic media disclosed herein, particularly those including a first granular magnetic recording layer with grain boundary material comprising primarily BN and a second granular magnetic recording layer with a grain boundary material comprising primarily an oxide. Comparative examples are also provided to illustrate the differences between conventional magnetic media and the illustrative embodiments of the novel magnetic media disclosed herein. It is important to note that the following illustrative embodiments do not limit the invention in anyway. It should also be understood that variations and modifications of these illustrative embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention.
The perpendicular magnetic recording media described in the following illustrative embodiments and comparative examples were fabricated using an in-line high-speed sputtering apparatus. This apparatus included a plurality of process chambers for film formation, a dedicated chamber for heating, and a chamber for introducing and ejecting a substrate. Each of these process chambers was evacuated independently to a pressure of 1×10−4 Pa or lower, after which a carrier with a substrate mounted thereon was moved to each chamber in order to carry out successive processes. The substrate was heated in the dedicated heating chamber, where the temperature during heating was controlled by monitoring the time in which power to the heater was turned on. A thermocouple was used to measure the temperature for a proportional-integral-derivative (PID) temperature controller.
An atomic force microscope (AFM) was used to assess surface roughness of the perpendicular magnetic recording media described below. The mean squared value (Rq) of surface roughness was used as an indicator for assessing roughness.
Illustrative Embodiment 1 corresponds to a perpendicular magnetic recording medium having the basic structure of the medium 600 shown in
Unless otherwise specified, the composition of the magnetic recording layer(s) is indicated by volume ratio and molar ratio, whereas the composition of the other layers are indicated by molar ratio (atomic ratio).
Comparative Examples 1-3 correspond to three different perpendicular magnetic recording media, each of which have the basic structure of the medium 700 shown in
The perpendicular magnetic recording media corresponding to Comparative Examples 1-3 differ from one another only with respect to the segregant material 716 that surrounds the magnetic grains 718 in their respective magnetic recording layer 710. For instance, Comparative Example 1 has a magnetic recording layer with an average composition of (Fe39Pt49Ag12)70(C)30 by volume ratio ((Fe45Pt45Ag10)60(C)40 by molar ratio). Comparative Example 2 has a magnetic recording layer with an average composition of (Fe39Pt49Ag12)70(BN)30 by volume ratio. Comparative Example 3 has a magnetic recording layer with an average composition of (Fe39Pt49Ag12)70(SiO2)30 by volume ratio.
Moreover, it is important to note that the perpendicular magnetic recording media corresponding to Comparative Examples 1-3 only include a single magnetic recording layer 710, whereas the perpendicular recording medium of Illustrative Embodiment 1 includes first and second magnetic recording layers.
Based on
Comparative Example 4 corresponds to a perpendicular magnetic recording medium having the basic structure of medium 600 shown in
Illustrative Embodiment 1 and Comparative Example 4 were assessed for recording width (RW).
As shown in
Accordingly, formation of a dual magnetic recording layer structure, where a first magnetic recording layer includes a grain boundary material with good grain separation, and where a second magnetic recording layer includes a grain boundary material having a thermal conductivity lower than FePt and a reduced surface roughness, may ultimately achieve a medium having good grain separation, low surface roughness and a narrow track width.
With respect to the vertical axis of
As indicated in both Table 1 and
It was further found that a comparable effect (such as that shown in Table 1 and
With respect to
As indicated in both Table 2 and
With respect to
As indicated in both Table 3 and
With respect to
Illustrative Embodiments 2-11 correspond to different perpendicular magnetic recording media, each of which have the basic structure of medium 600 shown in
As discussed previously with respect to the perpendicular recording medium of Illustrative Embodiment 1, the recording width was narrowed even in approaches where the grain boundary material of the second magnetic recording layer included an oxide other than SiO2. Consequently, various oxide-based grain boundary materials for use in this second magnetic recording layer were investigated as to crystallinity and corrosion resistance. Each of the media associated with Illustrative Embodiments 1-11 differ only with respect to the grain boundary composition in the second magnetic recording layer.
In order to investigate the crystallinity of the grain boundary material of the second magnetic recording layer, the degree of L10 ordering of the FePt magnetic grains therein was investigated. The degree of ordering was assessed by using an X-ray diffractometer to investigate the intensity ratio of the ordering line; specifically, the integrated intensity ratio I001/I002 of the (001) diffraction peak and the (002) diffraction peak. The greater the intensity ratio, the more advanced the degree of ordering. Moreover, dispersion of the crystal orientation of FePt was also investigated. An X-ray diffractometer was used to investigate crystal orientation by measuring Δθ50 of the (002) diffraction peak. The smaller the angle, the lower the dispersion of orientation.
In order to investigate the corrosion resistance of the grain boundary material of the second magnetic recording layer, an accelerated test was carried out in a constant-temperature tank in which the media of Illustrative Embodiments 1-11 were exposed to three cycles of increasing temperature from room temperature to 70° C. and 90% relative humidity. The media was further held for 100 h at the elevated condition corresponding to 70° C. and 90% relative humidity and subsequently cooled to room temperature after each cycle. The number of defects in the second magnetic recording layer was then investigated at the conclusion of this accelerated test. The number of defects for the medium of Illustrative Embodiment 1 after the accelerated test was taken as the standard. The lower the number of defects, the better the corrosion resistance.
Table 5 summarizes the results for the crystallinity and corrosion resistance associated with the grain boundary materials present in the second magnetic recording layers of the media associated with Illustrative Embodiments 1-11.
As indicated in Table 5, approaches where SiO2 was used for the oxide exhibited good integrated intensity ratios and crystal orientation. In approaches where MgO was used for the oxide, the crystal orientation of the second magnetic recording layer was better as compared to approaches using SiO2. Further, in approaches where TiO2 was used, the crystal orientation was better given the improved integrated intensity ratio I001/I002 as compared to approaches using SiO2. Finally, in approaches where Cr2O3 was used for the oxide, corrosion resistance was better as compared to approaches using SiO2.
It should also be noted that methodology presented herein for at least some of the various embodiments may be implemented, in whole or in part, in computer hardware, software, by hand, using specialty equipment, etc. and combinations thereof.
Moreover, any of the structures and/or steps may be implemented using known materials and/or techniques, as would become apparent to one skilled in the art upon reading the present specification.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of an embodiment of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.