HEXAGONAL STRONTIUM FERRITE MAGNETIC POWDER AND METHOD OF MANUFACTURING THE SAME, AND MAGNETIC RECORDING MEDIUM AND METHOD OF MANUFACTURING THE SAME

• US 20130256584A1
• Filed: 03/15/2013
• Published: 10/03/2013
• Est. Priority Date: 03/30/2012
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: YAMAZAKI, Nobuo, SUZUKI, Hiroyuki
• Granted Patent: US 9,478,331 B2
• Time in Patent Office: Days
• US Class Current: 252/62.58
• CPC Class Codes: C01G 49/0036 containing one alkaline earth metal, magnesium or lead
• CPC Class Codes: C01P 2004/04 obtained by TEM, STEM, STM or AFM
• CPC Class Codes: C01P 2006/42 Magnetic properties
• CPC Class Codes: C04B 2235/3213 Strontium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3215 Barium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/3251 Niobium oxides, niobates, tantalum oxides, tantalates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3284 Zinc oxides, zincates, cadmium oxides, cadmiates, mercury oxides, mercurates or oxide forming salts thereof
• CPC Class Codes: C04B 2235/421 Boron
• CPC Class Codes: C04B 2235/442 Carbonates
• CPC Class Codes: C04B 2235/767 Hexagonal symmetry, e.g. beta-Si3N4, beta-Sialon, alpha-SiC or hexa-ferrites
• CPC Class Codes: C04B 35/2683 Other ferrites containing alkaline earth metals or lead
• CPC Class Codes: H01F 1/01 of inorganic materials H01F1/44 takes precedence
• CPC Class Codes: H01F 1/11 in the form of particles for magnetic record carriers G11B5/70626

Abstract

An aspect of the present invention relates to a method of manufacturing hexagonal strontium ferrite magnetic powder, which comprises melting a starting material mixture which has a composition, as a composition converted into an oxide, lying within a region enclosed by the following four points:

• (a) SrO=48.0 mol %, Fe₂O₃=17.2 mol %, B₂O₃=34.8 mol %;
• (b) SrO=55.9 mol %, Fe₂O₃=17.7 mol %, B₂O₃=26.4 mol %;
• (c) SrO=41.7 mol %, Fe₂O₃=40.9 mol %, B₂O₃=17.4 mol %;
• (d) SrO=36.7 mol %, Fe₂O₃=40.1 mol %, B₂O₃=23.2 mol %;
  in a ternary diagram with SrO, Fe₂O₃, which may include an Fe substitution element, and B₂O₃ as apexes, to provide a melt, and quenching the melt to obtain a solidified product; and heat treating the solidified product to precipitate hexagonal strontium ferrite magnetic particles within the solidified product.

Claims

1. A method of manufacturing hexagonal strontium ferrite magnetic powder, which comprises:

melting a starting material mixture which has a composition, as a composition converted into an oxide, lying within a region enclosed by the following four points;

(a) SrO=48.0 mol %, Fe₂O₃=17.2 mol %, B₂O₃=34.8 mol %;

(b) SrO=55.9 mol %, Fe₂O₃=17.7 mol %, B₂O₃=26.4 mol %;

(c) SrO=41.7 mol %, Fe₂O₃=40.9 mol %, B₂O₃=17.4 mol %;

(d) SrO=36.7 mol %, Fe₂O₃=40.1 mol %, B₂O₃=23.2 mol %;

in a ternary diagram with SrO, Fe₂O₃, which may include an Fe substitution element, and B₂O₃ as apexes, to provide a melt, and quenching the melt to obtain a solidified product; and

heat treating the solidified product to precipitate hexagonal strontium ferrite magnetic particles within the solidified product.

2. The method of manufacturing hexagonal strontium ferrite magnetic powder according to claim 1, wherein the composition of the starting material mixture lies within a region enclosed by the following points:

(e) SrO=48.3 mol %, Fe₂O₃=17.2 mol %, B₂O₃=34.5 mol %;

(f) SrO=55.9 mol %, Fe₂O₃=17.7 mol %, B₂O₃=26.4 mol %;

(g) SrO=42.8 mol %, Fe₂O₃=39.1 mol %, B₂O₃=18.1 mol %;

in the ternary diagram.

3. The method of manufacturing hexagonal strontium ferrite magnetic powder according to claim 1, wherein the heat treatment provides precipitated hexagonal strontium ferrite magnetic particles with an activation volume ranging from 1,000 to 2,100 nm³.

4. The method of manufacturing hexagonal strontium ferrite magnetic powder according to claim 2, wherein the heat treatment provides precipitated hexagonal strontium ferrite magnetic particles with an activation volume ranging from 1,000 to 2,100 nm³.

5. The method of manufacturing hexagonal strontium ferrite magnetic powder according to claim 1, which comprises conducting the heat treatment by heating and maintaining the solidified product in a temperature region ranging from 600°

C. to 750°

C.

6. The method of manufacturing hexagonal strontium ferrite magnetic powder according to claim 2, which comprises conducting the heat treatment by heating and maintaining the solidified product in a temperature region ranging from 600°

C. to 750°

C.

7. The method of manufacturing hexagonal strontium ferrite magnetic powder according to claim 3, which comprises conducting the heat treatment by heating and maintaining the solidified product in a temperature region ranging from 600°

C. to 750°

C.

8. The method of manufacturing hexagonal strontium ferrite magnetic powder according to claim 4, which comprises conducting the heat treatment by heating and maintaining the solidified product in a temperature region ranging from 600°

C. to 750°

C.

9. Hexagonal strontium ferrite magnetic powder prepared by the method of manufacturing according to claim 1.

10. The hexagonal strontium ferrite magnetic powder according to claim 9, which has an activation volume ranging from 1,000 to 2,100 nm³.

11. The hexagonal strontium ferrite magnetic powder according to claim 9, which has a saturation magnetization ranging from 40 to 60 A·

m²/kg.

12. The hexagonal strontium ferrite magnetic powder according to claim 10, which has a saturation magnetization ranging from 40 to 60 A·

m²/kg.

13. The hexagonal strontium ferrite magnetic powder according to claim 9, which has a thermal stability in the form of KuV/kT of equal to or greater than 50, wherein Ku denotes an anisotropy constant, V denotes an activation volume, k denotes a Boltzmann constant, and T denotes an absolute temperature.

14. The hexagonal strontium ferrite magnetic powder according to claim 10, which has a thermal stability in the form of KuV/kT of equal to or greater than 50, wherein Ku denotes an anisotropy constant, V denotes an activation volume, k denotes a Boltzmann constant, and T denotes an absolute temperature.

15. The hexagonal strontium ferrite magnetic powder according to claim 11, which has a thermal stability in the form of KuV/kT of equal to or greater than 50, wherein Ku denotes an anisotropy constant, V denotes an activation volume, k denotes a Boltzmann constant, and T denotes an absolute temperature.

16. The hexagonal strontium ferrite magnetic powder according to claim 12, which has a thermal stability in the form of KuV/kT of equal to or greater than 50, wherein Ku denotes an anisotropy constant, V denotes an activation volume, k denotes a Boltzmann constant, and T denotes an absolute temperature.

17. The hexagonal strontium ferrite magnetic powder according to claim 9, which is employed for magnetic recording.

18. A magnetic recording medium, which comprises a magnetic layer containing the hexagonal strontium ferrite magnetic powder according to claim 9 and a binder, on a nonmagnetic support.

19. A method of manufacturing a magnetic recording medium, which comprises:

conducting the method of manufacturing according to claim 1 to provide hexagonal strontium ferrite magnetic powder; and

preparing a magnetic layer with a magnetic coating material which comprises the hexagonal strontium ferrite magnetic powder.