# US 10,373,638 B2 · Hexagonal ferrite powder and magnetic recording medium

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- Number: US 10,373,638 B2
- Document ID: US10373638B2
- Status: Granted
- Kind: B2
- Application number: 15/475,615
- Filed: 2017-03-31
- Published: 2017-10-05
- Granted: 2019-08-06
- Earliest claimed: 2016-03-31
- Assignees: FUJIFILM Corporation
- Applicants: FUJIFILM Corporation
- Inventors: Yoichi Hosoya; Masashi Shirata
- Web page: https://patentgrep.com/patent/US10373638B2

## CPC

- G11B 5/70615: {containing Fe metal or alloys (G11B5/70621 takes precedence)}
- G11B 5/70678: {Ferrites}
- G11B 5/714: characterised by the dimension of the magnetic particles
- G11B 5/78: Tape carriers
- H01F 1/11: in the form of particles {(for magnetic record carriers G11B5/70626)}
- B82Y 25/00: Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
- H01F 1/0063: {in a non-magnetic matrix, e.g. granular solids (granular films H01F10/007)}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES

## Abstract

Hexagonal ferrite powder has an average particle size falling within a range of 10 nm to 50 nm, a switching field distribution SFD23° 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 SFD23° C. (SFD−190° C./SFD23° C.) that is greater than 0.80.

## Claims

### Claim 1

Hexagonal ferrite powder, which has:
an average particle size falling within a range of 10 nm to 50 nm;
a switching field distribution SFD23° 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 SFD23° C., SFD−190° C./SFD23° C., falls within a range of 0.90 to 1.50.

### Claim 2 (depends on 1)

The hexagonal ferrite powder according to claim 1,
which has a saturation magnetization of greater than or equal to 30.0 A·m2/kg.

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

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

### Claim 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 SFD23° 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 SFD23° C., SFD−190° C./SFD23° C., falls within a range of 0.90 to 1.50.

### Claim 6 (depends on 5)

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·m2/kg.

### Claim 7 (depends on 5)

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.

### Claim 8 (depends on 5)

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.

### Claim 9 (depends on 5)

The magnetic recording medium according to claim 5,
wherein the SFD23° C. of the hexagonal ferrite powder is less than or equal to 0.60.