Magnetic powder, method of producing the same, and magnetic recording medium

Patent metadata

Field	Value
Publication number	US-11170813-B2
Application number	US-201716321327-A
Country	US
Kind code	B2
Filing date	Sep 27, 2017
Priority date	Oct 17, 2016
Publication date	Nov 9, 2021
Grant date	Nov 9, 2021

Abstract

A method of producing a magnetic powder includes performing heat treatment on first particles that contain ferrous oxide to prepare 5 second particles that contain ε-iron oxide.

First claim

The invention claimed is:

1. A magnetic recording medium, comprising:
a recording layer that includes particles containing ε-iron oxide including a ε-Fe 2 O 3 crystal,
wherein the ε-Fe 2 O 3 crystal includes a pure ε-Fe 2 O 3 crystal in which a Fe site is not substituted with another element,
wherein
δ/Mrt [nm/mA] satisfies a relationship represented by the following formula (2):
2.0≤δ/ Mrt≤ 120.0  (2),

wherein δ [nm] is an average thickness of the recording layer and Mrt [mA] is a product of a residual magnetization amount and a thickness of the recording layer,
wherein a ratio Y/X of a sub-peak height Y near a zero magnetic field to a main peak height X in an SFD (Switching Field Distribution) curve is not more than 0.5,
wherein a coefficient of variation is not more than 30%, and
wherein the coefficient of variation is represented by the following formula (1):
coefficient of variation [%]=([Standard deviation of particle diameter]/[Average particle diameter])×100. . . (1).

2. The magnetic recording medium according to claim 1 , wherein a squareness ratio in a direction perpendicular to the recording layer is not less than 60%.

3. The magnetic recording medium according to claim 1 , wherein each of the particles includes a core portion containing ε-iron oxide, and a shell portion containing α-Fe.

4. The magnetic recording medium according to claim 1 , wherein each of the particles includes a core portion containing ε-iron oxide, a first shell portion containing α-Fe, and a second shell portion that is provided on the first shell portion and contains iron oxide.

5. The magnetic recording medium according to claim 1 , wherein the ε-Fe 2 O 3 crystal is in a single phase.

6. The magnetic recording medium according to claim 1 , wherein the ε-Fe 2 O 3 crystal further includes an ε-Fe 2 O 3 metal crystal including a metal element in addition to iron.

7. The magnetic recording medium according to claim 6 , wherein the metal element includes one or more of Al, Ga, and In.

8. The magnetic recording medium according to claim 6 , wherein a molar ratio of the metal element (M) and Fe (M:Fe) is expressed as x:(2−x), where 0<x<1.

9. The magnetic recording medium according to claim 1 , further comprising a substrate and an underlayer provided on a main surface of the substrate, wherein the recording layer is provided on the underlayer.

10. The magnetic recording medium according to claim 9 , wherein the underlayer includes a nonmagnetic layer.

11. The magnetic recording medium according to claim 1 , wherein the coefficient of variation is not more than 20%.

Assignees

• Sony Corp

Inventors

• Muramatsu Atsushi
• Nakaya Masafumi
• Terakawa Masaru
• Maeshima Katsunori
• Yamaga Minoru

Classifications

• B22F1/00

  Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties · CPC title

• B22F1/18

  Non-metallic particles coated with metal · CPC title

• H01F1/112

  with a skin (H01F1/113 takes precedence) · CPC title

• G11B5/70678

  Ferrites · CPC title

• B22F2301/35

  Iron · CPC title