Magnetic particle and method of preparing the same, and magnetic recording medium

• US 8,524,108 B2
• Filed: 01/20/2011
• Issued: 09/03/2013
• Est. Priority Date: 01/21/2010
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: Hattori, Yasushi
• Primary Examiner(s): Koslow, Carol M
• Application Number:
  US13/010,524
• Publication Number:
  US 20110175014A1
• Time in Patent Office: 957 Days
• Field of Search: 252 6256- 6264
• US Class Current: 252/62.63
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01G 49/0036 containing one alkaline earth metal, magnesium or lead
• CPC Class Codes: C01P 2004/24 Nanoplates, i.e. plate-like particles with a thickness from 1-100 nanometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2006/12 Surface area
• CPC Class Codes: C01P 2006/42 Magnetic properties
• CPC Class Codes: C09C 1/24 Oxides of iron
• CPC Class Codes: G11B 5/70678 Ferrites
• CPC Class Codes: H01F 1/065 obtained by a reduction
• CPC Class Codes: H01F 1/10 non-metallic substances, e.g. ferrites , e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure

Abstract

An aspect of the present invention relates to a magnetic particle obtained by heat-treating a hexagonal ferrite magnetic material in reducing atmosphere containing hydrocarbon gas.

Claims

1. A magnetic particle, which is obtained by heat-treating a hexagonal ferrite magnetic material having a coercive force of equal to or higher than 230 kA/m in a reducing atmosphere containing a hydrocarbon gas.

2. The magnetic particle according to claim 1, which comprises a carbon component.

3. The magnetic particle according to claim 2, wherein the carbon component is graphite.

4. The magnetic particle according to claim 1, wherein the reducing atmosphere is a mixed gas atmosphere of a hydrocarbon gas and an inert gas.

5. The magnetic particle according to claim 4, wherein the hydrocarbon gas is at least one selected from the group consisting of methane and ethane.

6. The magnetic particle according to claim 1, which has a coercive force of equal to or higher than 120 kA/m but less than 230 kA/m.

7. The magnetic particle according to claim 1, which has thermal stability in the form of a gradient of decay of magnetization over time of equal to or less than 0.005 (1/ln(s)).

8. The magnetic particle according to claim 1, which has thermal stability in the form of a difference of a decay rate A and a decay rate B, B−

A, ranging from 0.0001 to 0.001, wherein the decay rate A is measured by saturating magnetization of the magnetic particle with an external magnetic field of 40,000 Oe at a temperature of 300 K, subsequently changing the external magnetic field to −

600 Oe, and measuring the decay rate based on a time at which a demagnetizing field reaches 600 Oe, and the decay rate B is measured by heating the magnetic particle of which the decay rate A has been measured to 320 K at a rate of temperature increase of 5°

C/minute, maintaining the magnetic particle for 10 minutes at that temperature, subsequently cooling the magnetic particle to 300 K at a rate of temperature decrease of 5°

C/minute, and measuring the decay rate by the same method as that of the decay rate A.

9. A magnetic particle, which is comprised of a hexagonal ferrite magnetic material in which α

-Fe and a carbon component are detected by X-ray diffraction analysis, and

which has a coercive force of equal to or higher than 120 kA/m but less than 230 kA/m.

10. The magnetic particle according to claim 9, wherein a quantity of α

-Fe detected by X-ray diffraction ranges from 0.2 to 1.0 weight percent.

11. The magnetic particle according to claim 9, wherein the carbon component is graphite.

12. The magnetic particle according to claim 9, which has thermal stability in the form of a gradient of decay of magnetization over time of equal to or less than 0.005 (1/ln(s)).

13. The magnetic particle according to claim 9, which has thermal stability in the form of a difference of a decay rate A and a decay rate B, B−

A, ranging from 0.0001 to 0.001 , wherein the decay rate A is measured by saturating magnetization of the magnetic particle with an external magnetic field of 40,000 Oe at a temperature of 300 K, subsequently changing the external magnetic field to −

600 Oe, and measuring the decay rate based on a time at which a demagnetizing field reaches 600 Oe, and the decay rate B is measured by heating the magnetic particle of which the decay rate A has been measured to 320 K at a rate of temperature increase of 5°

C/minute, maintaining the magnetic particle for 10 minutes at that temperature, subsequently cooling the magnetic particle to 300 K at a rate of temperature decrease of 5°

C/minute, and measuring the decay rate by the same method as that of the decay rate A.

20. A magnetic recording medium comprising a magnetic layer comprising a ferromagnetic powder and a binder, wherein the ferromagnetic powder comprises the magnetic particle according to claim 9.

14. A method of preparing a magnetic particle, which comprises heat-treating a hexagonal ferrite magnetic material having a coercive force of equal to or higher than 230 kA/m in a reducing atmosphere containing a hydrocarbon gas.

15. The method of preparing a magnetic particle according to claim 14, wherein the reducing atmosphere is a mixed gas atmosphere of a hydrocarbon gas and an inert gas.

16. The method of preparing a magnetic particle according to claim 14, wherein the hydrocarbon gas is at least one selected from the group consisting of methane and ethane.

17. The method of preparing a magnetic particle according to claim 14, wherein the heat-treatment yields a magnetic particle having a coercive force lower than that of the hexagonal ferrite magnetic material prior to the heat-treatment.

18. The method of preparing a magnetic particle according to claim 14, wherein the heat-treatment yields a magnetic particle having a coercive force of equal to or higher than 120 kA/m but less than 230 kA/m.

19. The method of preparing a magnetic particle according to claim 14, wherein the heat-treatment is conducted at a temperature ranging from 200 to 400°

C.