Hexagonal ferrite powder and magnetic recording medium

Patent metadata

Field	Value
Publication number	US-10373638-B2
Application number	US-201715475615-A
Country	US
Kind code	B2
Filing date	Mar 31, 2017
Priority date	Mar 31, 2016
Publication date	Aug 6, 2019
Grant date	Aug 6, 2019

Abstract

Hexagonal ferrite powder has an average particle size falling within a range of 10 nm to 50 nm, a switching field distribution SFD 23° C. measured at a temperature of 23° C. that is less than or equal to 0.80, and a ratio of a switching field distribution SFD −190° C. that is measured at a temperature of −190° C. to the SFD 23° C. (SFD −190° C. /SFD 23° C. ) that is greater than 0.80.

First claim

What is claimed is:

1. Hexagonal ferrite powder, which has:
an average particle size falling within a range of 10 nm to 50 nm;
a switching field distribution SFD 23° C. measured at a temperature of 23° C. falls within a range of 0.10 to 0.60; and
a ratio of a switching field distribution SFD −190° C. that is measured at a temperature of −190° C. to the SFD 23° C. , SFD −190° C. /SFD 23° C. , falls within a range of 0.90 to 1.50.

2. The hexagonal ferrite powder according to claim 1 ,
which has a saturation magnetization of greater than or equal to 30.0 A·m 2 /kg.

3. The hexagonal ferrite powder according to claim 1 ,
which has a coercive force of greater than or equal to 159 kA/m.

4. The hexagonal ferrite powder according to claim 1 ,
wherein the average particle size falls within a range of 10 nm to 35 nm.

5. A magnetic recording medium,
which comprises a magnetic layer comprising ferromagnetic powder and binder on a nonmagnetic support,
wherein the ferromagnetic powder is hexagonal ferrite powder which has:
an average particle size falling within a range of 10 nm to 50 nm;
a switching field distribution SFD 23° C. measured at a temperature of 23° C. falls within a range of 0.10 to 0.60; and
a ratio of a switching field distribution SFD −190° C. that is measured at a temperature of −190° C. to the SFD 23° C. , SFD −190° C. /SFD 23° C. , falls within a range of 0.90 to 1.50.

6. The magnetic recording medium according to claim 5 ,
wherein the hexagonal ferrite powder has a saturation magnetization of greater than or equal to 30.0 A·m 2 /kg.

7. The magnetic recording medium according to claim 5 ,
wherein the hexagonal ferrite powder has a coercive force of greater than or equal to 159 kA/m.

8. The magnetic recording medium according to claim 5 ,
wherein the average particle size of the hexagonal ferrite powder falls within a range of 10 nm to 35 nm.

9. The magnetic recording medium according to claim 5 ,
wherein the SFD 23° C. of the hexagonal ferrite powder is less than or equal to 0.60.

Assignees

• Fujifilm Corp

Inventors

• Hosoya Yoichi
• Shirata Masashi

Classifications

• B82Y25/00

  Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance · CPC title

• G11B5/78

  Tape carriers · CPC title

• H01F1/0063

  in a non-magnetic matrix, e.g. granular solids (granular films H01F10/007) · CPC title

• G11B5/70678 Primary

  Ferrites · CPC title

• H01F1/11

  in the form of particles {(for magnetic record carriers G11B5/70626)} · CPC title