Textured planar m-type hexagonal ferrites and methods of use thereof
A grain-oriented M-type hexagonal ferrite has the formula MeFe 12 O 19 , and a dopant effective to provide planar magnetic anisotropy and magnetization in a c-plane, or a cone anisotropy, in the hexagonal crystallographic structure wherein Me is Sr + , Ba 2+ or Pb 2+ , and wherein greater than 30%, preferably greater than 80%, of c-axes of the ferrite grains are aligned perpendicular to the c-plane.
1. A grain-oriented M-type hexagonal ferrite having the formula
MeFe 12 O 19 ,
and a dopant effective to provide planar magnetic anisotropy and magnetization in a c-plane, or a cone anisotropy, in the hexagonal crystallographic structure, wherein Me is Sr + , Ba 2+ or Pb 2+ , and
wherein greater than 30% of grains of the ferrite are aligned along the c-axis of the crystal structure, perpendicular to the c-plane;
wherein the dopant comprisese Co 2+ /Ti 4+ , Co 2+ /Zr 4+ , Co 2+ /Sn 4+ , Co 2+ /Ir 4′ , Bi 2+ /Co 2+ /Ti 4+ , Bi 2+ /Co 2+ /Zr 4+ , Bi 2+ /Co 2+ /Sn 4+ , or a combination thereof.
2. The grain-oriented M-type hexagonal ferrite of claim 1 , having the formula Bi x —Ba 1−x (CoTi) y Fe 12−2y O 19 (x=0-0.8, y=0.5-1.5), Ba(CoTi) x Fe 12−2x O 19 (x=0.5-1.5), Ba(CoZr) x Fe 12−2x O 19 (x=0.5-1.5), Ba(CoSn) x Fe 12−2x O 19 (x=0.5-1.5), Ba(CoIr) x Fe 12−2x O 19 (x=0.5-1.5), Bi x Sr 1−x (CoTi) y —Fe 12−2y O 19 (x=0-0.8, y=0.5-1.5), Sr(CoTi) x Fe 12−2x O 19 (x=0.5-1.5), Sr(CoZr) x Fe 12−2x O 19 (x=0.5-1.5), Sr(CoSn) x Fe 12−2x O 19 (x=0.5-1.5), or Pb(CoTi) x Fe 12−2x O 19 (x=0.5-1.5).
3. The grain-oriented M-type hexagonal ferrite of claim 1 , having the formula Bi x Ba 1−x (CoTi) y Fe 12−2y O 19 (x=0-0.8, y=0.5-1.5), Ba(CoTi) x Fe 12−2x O 19 (x=0.5-1.5), Ba(CoZr) x Fe 12−2x O 19 (x=0.5-1.5), or Ba(CoSn) x Fe 12−2x O 19 (x=0.5-1.5).
4. The grain-oriented M-type hexagonal ferrite of claim 1 , wherein Me is Ba 2+ with substitution of Sr for Ba in part, and having the formula (Bi x Sr y Ba 1−x−y )(CoTi) z Fe 12−2z O 19 (x=0-0.8, y=0-1, z=0.5-2.0).
5. The grain-oriented M-type hexagonal ferrite having the formula
MeFe 12 O 19 ,
and a dopant effective to provide planar magnetic anisotropy and magnetization in a c-plane, or an easy cone anisotropy, in the hexagonal crystallographic structure, wherein Me is Sr 2+ , Ba 2+ or Pb 2+ , and
wherein greater than 30% of grains of the ferrite are aligned along the c-axis of the crystal structure, perpendicular to the c-plane,
wherein the grain-oriented M-type hexagonal ferrite has at least one of
an in-plane permeability of greater than 50 over an operating frequency of 50 MHz-300 MHz;
a magnetic loss tangent of less than 0.5 at 100 MHz;
a dielectric loss tangent of less than 0.02 over 0-300 MHz; or
a dielectric constant that is 10-30 over 30-300 MHz.
6. The grain-oriented M-type hexagonal ferrite of claim 5 , wherein the grain-oriented M-type hexagonal ferrite has
a magnetic loss tangent of less than 0.2 over 30-300 MHz; and
a dielectric loss tangent of less than 0.05 over 30-300 MHz.
7. The grain-oriented M-type hexagonal ferrite of claim 5 , wherein the grain-oriented M-type hexagonal ferrite has
an in-plane permeability of greater than 80 at an operating frequency over 50-300 MHz; and
a magnetic loss tangent of less than 0.2 at 100 MHz.
8. The grain-oriented M-type hexagonal ferrite of claim 1 , wherein the hexagonal ferrite has a sintered density of at least 85% of a theoretical density.
9. The grain-oriented M-type hexagonal ferrite of claim 1 , wherein the grain size in the c-plane is up to 300 μm.
10. An article comprising the grain-oriented M-type hexagonal ferrite of claim 1 .
11. The article of claim 10 , wherein the article is an inductor, a perpendicular magnetic record, an antenna, a microwave absorber, an electromagnetic interference suppressor, or a shielding material.
12. A wireless power device or near-field communication device comprising the shielding material of claim 11 .
13. A method of making a doped, grain-oriented M-type hexagonal ferrite of claim 1 , the method comprising
preparing a ferrite of the formula
MeFe 12 O 19
comprising a dopant effective to provide planar magnetic anisotropy and magnetization in the c-plane, or a cone anisotropy, wherein Me is Sr + , Ba 2+ or Pb 2+ ;
aligning the ferrite such that greater than 30% of grains of the ferrite are aligned along the c-axis of the crystal structure perpendicular to the c-plane, to provide the doped, grain-oriented M-type hexagonal ferrite; and
optionally sintering the doped, grain-oriented M-type hexagonal ferrite at a temperature of greater than 800° C. to provide a sintered material having a density of at least 85% of a theoretical density;
wherein the dopant comprises Co 2+ /Ti 4+ , Co 2+ /Zr 4+ , Co 2+ /Sn 4+ , Co 2+ /Ir 4+ , Bi 2+ /Co 2+ /Ti 4+ , Bi 2+ /Co 2+ /Zr 4+ , Bi 2+ /Co 2+ /Sn 4+ , or a combination thereof.
14. The method of claim 13 , wherein the dopant is provided by substituting a portion of the Fe with CoTi, CoZr, or CoSn.
15. The method of claim 13 , wherein preparing the ferrite comprises calcining a dry powder comprising a MeFe 12 O 19 precursor, a sol-gel process, a molten salt process, a co-precipitation process, a hydrothermal process, a sol gel hydrothermal process, or another chemical synthesis process.
16. The method of claim 13 , wherein aligning the ferrite comprises applying a rotating in-plane magnetic field to the ferrite while applying vertical mechanical pressure to the ferrite, applying a mechanical shearing force to the ferrite with or without applying a magnetic field applied, or a combination thereof.
17. The method of claim 16 , wherein aligning the ferrite comprises applying a rotating in-plane magnetic field having a magnetic field has a strength of greater than 2000 Oe.
18. The method of claim 13 , comprising, during aligning the ferrite, shaping the grain-oriented M-type hexagonal ferrite.
19. The method of claim 13 , comprising, prior to sintering, cutting the grain-oriented M-type hexagonal ferrite to a specified dimension.