Magnetic recording medium

• US 6,994,925 B2
• Filed: 10/21/2004
• Issued: 02/07/2006
• Est. Priority Date: 10/22/2003
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Masaki, Kouichi
• Primary Examiner(s): Resan, Stevan A.
• Application Number:
  US10/968,951
• Publication Number:
  US 20050089722A1
• Time in Patent Office: 474 Days
• Field of Search: 428/842.8
• US Class Current: 428/842.8
• CPC Class Codes: G11B 5/70 on a base layer
• CPC Class Codes: G11B 5/70678 Ferrites
• CPC Class Codes: G11B 5/714 characterised by the dimension of the magnetic particles

Abstract

To provide a magnetic recording medium which undergoes little effect of thermal fluctuation and provides a high short wavelength output and C/N ratio when reproduction is conducted using MR head, the magnetic recording medium includes a non-magnetic layer having a non-magnetic powder dispersed in a binder provided on a support and a magnetic layer having a ferromagnetic powder dispersed in a binder provided on the non-magnetic layer, wherein the ferromagnetic powder comprises a hexagonal ferrite magnetic powder having an average diameter of from 10 to 35 nm and a coercive force of from 135 to 400 kA/m; the magnetic layer has a coercive force of from 135 to 440 kA/m; and a product of an anisotropic magnetic field of the magnetic layer and an average particle volume of the hexagonal ferrite magnetic powder is from 1.2×10⁶ to 2.4×10⁶ kA/m·nm³.

Claims

1. A magnetic recording medium, which comprises:

a support;

a non-magnetic layer comprising a binder and a non-magnetic powder; and

a magnetic layer comprising a binder and a ferromagnetic powder,

wherein the ferromagnetic powder comprises a hexagonal ferrite magnetic powder having an average diameter of from 10 to 35 nm and a coercive force of from 135 to 400 kA/m;

the magnetic layer has a coercive force of from 135 to 440 kA/m; and

a product of an anisotropic magnetic field of the magnetic layer and an average particle volume of the hexagonal ferrite magnetic powder is from 1.2×

10⁶ to 2.4×

10⁶ kA/m·

nm³.

2. The magnetic recording medium according to claim 1, wherein the average particle volume of the hexagonal ferrite magnetic powder is from 2,000 to 5,000 nm³.

3. The magnetic recording medium according to claim 1, wherein the anisotropic magnetic field is from 239 to 1,200 kA/m.

4. The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 0.01 to 0.5 μ

m.

5. The magnetic recording medium according to claim 1, wherein the magnetic layer satisfies a condition that a product of a residual magnetic flux density and a thickness is from 5 to 100 mT·

μ

m.

6. The magnetic recording medium according to claim 1, wherein the hexagonal ferrite magnetic powder comprises at least one of a barium ferrite, a strontium ferrite, a lead ferrite and a calcium ferrite.

7. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder has an average thickness of from 2 to 15 nm.

8. The magnetic recording medium according to claim 1, wherein the hexagonal ferrite magnetic powder has an average aspect ratio of from 1.5 to 4.