Magnetic recording medium

• US 20020132140A1
• Filed: 08/30/2001
• Published: 09/19/2002
• Est. Priority Date: 03/19/2001
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Hitachi, Ltd.
• Inventors: Igarashi, Masukazu, Zaitsu, Hideki, Akagi, Fumiko, Tomiyama, Futoshi
• Granted Patent: US 6,635,367 B2
• Time in Patent Office: Days
• US Class Current: 428/694TM
• CPC Class Codes: G11B 5/66 the record carriers consisting of several layers
• CPC Class Codes: G11B 5/676 having magnetic layers separated by a nonmagnetic layer, e.g. antiferromagnetic layer, Cu layer or coupling layer
• CPC Class Codes: Y10S 428/90 Magnetic feature
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree

Abstract

An object is to provide a magnetic recording medium giving high resolution, low noise and little thermal fluctuation and thus suitable for high density magnetic recording, and a high-capacity magnetic recording device realized by using this medium. A thin film type magnetic recording medium is used, having at least 2 magnetic layers formed on a non-magnetic substrate and a non-magnetic intermediate layer that is interposed between the magnetic layers and causes the magnetizations of the magnetic layers to be anti-parallel to one another, and wherein the ratio HkB/HkA of the anisotropic magnetic field strength HkB of the magnetic layer on the side near to the substrate to the anisotropic magnetic field strength HkA of the magnetic layer on the side far from the substrate is 0.7 or less, more preferably at least 0.4 and not more than 0.65.

Claims

1. A thin film type magnetic recording medium, having:

at least 2 magnetic layers formed on a non-magnetic substrate; and

a non-magnetic intermediate layer that is interposed between said magnetic layers and causes magnetizations of said magnetic layers to be anti-parallel to one another;

wherein a ratio HkB/HkA of an anisotropic magnetic field strength HkB of a magnetic layer on a side near to said substrate to an anisotropic magnetic field strength HkA of a magnetic layer on a side far from said substrate is 0.7 or less.

2. The magnetic recording medium according to claim 1, wherein said ratio HkB/HkA is at least 0.4 and not more than 0.65.

3. The magnetic recording medium according to claim 1, wherein a ratio HcoB/HcoA of a coercivity HcoB of the magnetic layer B on the side near to said substrate at 0 K as obtained by extrapolating values of coercivity at 200 K and 100 K to a coercivity HcoA of the magnetic layer A on the side far from said substrate at 0 K as obtained by extrapolating values of coercivity at 200 K and 100 K is 0.7 or less.

4. The magnetic recording medium according to claim 3, wherein said ratio HcoB/HcoA is at least 0.4 and not more than 0.65.

5. The magnetic recording medium according to claim 1, wherein a value (HcoA−

HcoB)/(π

a*dH/dx) is 0.8 or more, where HcoB is a coercivity of the magnetic layer B on the side near to said substrate at 0 K as obtained by extrapolating values thereof at 200 K and 100 K, HcoA is a coercivity of the magnetic layer A on the side far from said substrate at 0 K as obtained by extrapolating values thereof at 200 K and 100 K, dH/dx is a derivative in a track direction of a track direction component of a magnetic field from a magnetic recording head used together with said magnetic recording medium in a magnetic recording/playback device, taken in a position where said track direction component is HcoA in the center of the track and the center of the thickness direction of said magnetic layer A, and π

a is a magnetic transition width of an isolated transition formed on said magnetic recording medium using said magnetic recording head.

6. The magnetic recording medium according to claim 5, wherein said value (HcoA−

HcoB)/(π

a*dH/dx) is at least 0.9 and not more than 1.5.

9. The magnetic recording medium according to claim 1, where in during a process in which, at a temperature of 30 K, a magnetic field is applied in a track direction to cause magnetic saturation, then the magnetic field is reduced at a rate of 3,000 A/m per second, and then a magnetic field is applied in an opposite direction to cause magnetic saturation, the derivative of magnetization with respect to magnetic field strength has at least 2 peaks, and the magnetic field strengths giving said peaks are all in said direction of the last magnetic saturation.

10. The magnetic recording medium according to claim 9, wherein during a process in which, at a temperature of 135 K, a magnetic field is applied in the track direction to cause magnetic saturation, then the magnetic field is reduced at a rate of 3,000 A/m per second, and then a magnetic field is applied in the opposite direction to cause magnetic saturation, the derivative of magnetization with respect to magnetic field strength has at least 2 peaks, and at least one of the magnetic field strengths giving said peaks is in said direction of the last magnetic saturation.

11. The magnetic recording medium according to claim 1, wherein said magnetic recording medium comprises at least 2 magnetic layers formed on a non-magnetic substrate;

and a non-magnetic intermediate layer that is interposed between said magnetic layers and causes magnetizations of said magnetic layers to be anti-parallel to one another, and wherein a saturation magnetization of said magnetic layer on a side near to said substrate is larger than a saturation magnetization of said magnetic layer on a side far from said substrate.

12. The magnetic recording medium according to claim 1, wherein said magnetic layer on a side near to said substrate comprises either Co, or an alloy having Co as a principal component and also containing at least one element selected from Fe, Ni, Cr, Ta, Pt and Pd, and also preferably containing B (boron).

13. The magnetic recording medium according to claim 1, wherein said non-magnetic intermediate layer comprises an alloy containing at least 50 at % of at least one metallic element selected from the group consisting of Ru, Ir, Rh, Re, Cu, Cr and Al, or an alloy containing a total of at least 50 at % of at least one element selected from Ru, Ir and Rh and at least one element selected from Pt and Pd.

14. The magnetic recording medium according to claim 13, wherein said non-magnetic intermediate layer is formed using an RF sputtering method.

15. The magnetic recording medium according to claim 1, wherein said magnetic layer on a side far from said substrate comprises a crystalline magnetic material containing at least 50 at % of at least one metallic element selected from the group consisting of Co, Fe and Ni, and said magnetic layer on a side near to said substrate is formed on a non-magnetic ground layer containing at least 50 at % of at least one element selected from the group consisting of Cr, Mo, W, Ta, V, Nb, Ti, Ge, Si, Co and Ni.

16. A magnetic storage device that carries out playback of magnetic information, and which combines the magnetic recording medium according to claim 1 and a magnetic head having a playback element that uses a giant magneto-resistive effect element or a tunnel-coupled film exhibiting a magneto-resistive effect and has an effective track width of 0.5 μ

m or less.

17. The magnetic recording medium according to claim 5, having a recording unit which employs a head in which magnetic poles having a saturation magnetic flux density of at least 1.8 T are used.

7. A thin film type magnetic recording medium, having:

at least 2 magnetic layers formed on a non-magnetic substrate; and

a non-magnetic intermediate layer that is interposed between said magnetic layers and causes magnetizations of said magnetic layers to be anti-parallel to one another;

wherein a ratio KuB/KuA of a magnetic anisotropy energy KuB of a magnetic layer on a side near to said substrate to a magnetic anisotropy energy KuA of a magnetic layer on a side far from said substrate is 0.7 or less.

8. The magnetic recording medium according to claim 7, wherein said ratio KuB/KuA is at least 0.4 and not more than 0.65.