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Patent Issued for Perpendicular Magnetic Recording Medium (PMRM) and Magnetic Storage Device Using the Same

May 7, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Nakagawa, Hiroyuki (Yokohama, JP); Arai, Reiko (Odawara, JP); Tamai, Ichiro (Odawara, JP); Tanahashi, Kiwamu (Kokubunji, JP), filed on June 30, 2010, was published online on April 22, 2014.

The patent's assignee for patent number 8705208 is HGST Netherlands B.V. (Amsterdam, NL).

News editors obtained the following quote from the background information supplied by the inventors: "The heart of a computer is a magnetic disk drive 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 rapid increase in the volume of data handled by computers has furthered demand for increasing the capacity of hard disk devices as an auxiliary storage device. Moreover, with the increased use of hard disk devices in domestic electrical appliances, there is a strong demand for enhancing the capacity of and reducing the size of hard disk devices.

"In typical systems, a perpendicular magnetic recording system forms recording bits with the magnetization of the recording medium perpendicular to the media plane. Magnetizations within adjacent recorded bits run parallel to one another in opposite directions, reducing the demagnetization field within magnetized transitional regions, media noise, and stabilizing recorded magnetization during high-density recording. A double layered PMRM with a soft magnetic underlayer functions as a return path for the magnetic flux provided between the substrate and the perpendicularly magnetized recording layer. A magnetic head, including a magnetic shield with an interposing non-magnetic layer, is provided on at least the trailing side of the main magnetic pole to improve the recording magnetic field gradient.

"CoCrPt alloy which was conventionally used for longitudinal magnetic recording media was investigated for perpendicular magnetic recording media. In conventional recording layers, thermal phase separation is used to segregate non-magnetic material mainly comprising Cr from the grain boundaries and reduce noise. This process utilizes high concentrations of Cr to maximize noise reduction, with an undesirably high quantity of Cr remaining within the magnetic crystal grains. This high concentration of Cr in the magnetic crystal grains reduces magnetic anisotropic energy and stability of the recorded signal.

"To resolve these problems and reduce noise, state-of-the-art recording media employ a granular structure wherein magnetic crystal grains are separated magnetically by segregating non-magnetic compounds such as oxides and/or nitrides around the magnetic crystal grains. In case of a recording layer composed of a CoCrPt alloy with oxygen and oxide added, where the template for oxide-grain boundary formation is formed on the underlayer, allowing oxides to separate easily from the magnetic crystal grains, a granular structure of oxides surrounding magnetic crystal grains enables magnetic separation in the recording layer. It is therefore possible to decrease the amount of Cr contained in the magnetic crystal grains, enabling noise to be reduced without reducing the magnetic anisotropic energy.

"Current techniques for improving recording density in a perpendicular magnetic recording medium reduce the magnetic cluster size. This approach is limited because thermal instability occurs when recording density exceeds about 77.7 gigabits per square centimeter (approx 500 Gb/in.sup.2).

"One effective method of avoiding this instability is to use material with a large magnetic anisotropy in the perpendicular magnetic recording layer, and it is possible to increase the magnetic anisotropy in the CoCrPt granular magnetic layer by reducing the Cr concentration. However, the difficulty with reducing the concentration of Cr occurs where segregation of oxide from the crystal grain boundary is insufficient, strengthening the exchange coupling between the magnetic grains so that the magnetic cluster size rapidly increases and the signal-to-noise ratio (SNR) deteriorates. Moreover, if the segregation of oxides to the grain boundary is promoted and magnetic grains become isolated, the switching field increases, making it impossible to record with the write magnetic field from the head.

"Current state-of-the-art techniques reduce the magnetic field in which magnetization reversal occurs by thickening the non-granular magnetic layer which assists the magnetization reversal. However, there is an added difficulty with using this method in that non-granular magnetic layers have stronger lateral exchange coupling in the film plane than the granular layer, producing a larger magnetic cluster size with an increasing film thickness and deteriorating both resolution and the SNR. Therefore, a method and system for providing a perpendicular magnetic recording medium and a magnetic recording device which simultaneously satisfy the requirements for a high SNR, thermal stability, and write-ability would be very beneficial."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "In one embodiment, a perpendicular magnetic recording medium (PMRM) includes a substrate; a soft magnetic underlayer formed above the substrate; an underlayer formed above the soft magnetic underlayer, the underlayer being for controlling orientation and segregation of the magnetic layer; a magnetic layer formed above the underlayer, the magnetic layer comprising mainly Co, Cr, Pt, and oxides thereof; and a ferromagnetic metal layer formed above the magnetic layer, the ferromagnetic metal layer comprising mainly Co, Cr, and Pt, wherein the ferromagnetic metal layer does not include oxides. The magnetic layer containing oxides comprises more than two magnetic layers, and a Cr concentration of magnetic layer adjacent to the ferromagnetic metal layer is between about 23 at. % and about 32 at. %, and a Cr concentration and a difference of Cr concentration between the adjacent layers are less than about 32 at. % and 25 at. % respectively at all magnetic layers which exist between the oxide-containing magnetic layer adjacent to the ferromagnetic metal layer and a oxide-containing magnetic layer formed bellow with the lowest Cr concentration among oxide-containing magnetic layers, the magnetic layer with the lowest Cr concentration has a granular structure in which oxides surround ferromagnetic grains therein; and a nucleation field is higher than about 159.2 kA/m.

"In another embodiment, a PMRM includes a substrate; a soft magnetic underlayer formed above the substrate; an underlayer formed above the soft magnetic underlayer, the underlayer being for controlling orientation and segregation of the magnetic layer; a magnetic layer formed above the underlayer, the magnetic layer comprising Co, Cr, Pt, and oxides thereof, wherein the magnetic layer comprises at least three magnetic layers; and a ferromagnetic metal layer formed above the magnetic layer, the ferromagnetic metal layer comprising Co, Cr, and Pt, wherein the ferromagnetic metal layer does not include oxides. A Cr concentration of a magnetic layer adjacent to the ferromagnetic metal layer is between about 23 at. % and about 32 at. %, a Cr concentration of magnetic layers between the magnetic layer adjacent to the ferromagnetic metal layer and a magnetic layer having a lowest Cr concentration among the at least three magnetic layers is less than about 32 at. %, a difference between a Cr concentration of adjacent magnetic layers between the magnetic layer adjacent to the ferromagnetic metal layer and a magnetic layer having a lowest Cr concentration among the at least three magnetic layers is less than about 25 at. %, the magnetic layer having a lowest Cr concentration among the at least three magnetic layers has a granular structure in which oxides surround ferromagnetic grains therein, and a nucleation field is larger than about 159.2 kA/m.

"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 additional information on this patent, see: Nakagawa, Hiroyuki; Arai, Reiko; Tamai, Ichiro; Tanahashi, Kiwamu. Perpendicular Magnetic Recording Medium (PMRM) and Magnetic Storage Device Using the Same. U.S. Patent Number 8705208, filed June 30, 2010, and published online on April 22, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=56&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=2771&f=G&l=50&co1=AND&d=PTXT&s1=20140422.PD.&OS=ISD/20140422&RS=ISD/20140422

Keywords for this news article include: HGST Netherlands B.V.

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Source: Journal of Engineering


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