Disclosed herein are embodiments of an enhanced resonant frequency hexagonal ferrite material and methods of manufacturing. The hexagonal ferrite material can be Y-phase strontium hexagonal ferrite material. In some embodiments, sodium can be added into the crystal structure of the hexagonal ferrite material in order to achieve high resonance frequencies while maintaining high permeability.

A magnetic powder for a magnetic recording medium includes magnetic particles in which Ba in hexagonal barium ferrite is partially substituted with Sr, wherein a Dx volume represented by Dx volume (nm.sup.3) = Dxc × π × (Dxa/2).sup.2 is 2,200 nm.sup.3 or less, and an Sr/(Ba+Sr) molar ratio is 0.01 to 0.15. One that satisfies Ku ≥ 0.1 × [Sr/(Ba+Sr) molar ratio] + 0.13 is more preferred. For the formulas, Dxc is a crystallite diameter (nm) in a c-axis direction of a hexagonal ferrite crystal lattice, Dxa is a crystallite diameter (nm) in an a-axis direction of the same crystal lattice, π is a circular constant, and Ku is a magnetocrystalline anisotropy constant (MJ/m.sup.3). By providing the hexagonal ferrite magnetic powder formed of fine particles, an effect of improving the perpendicular squareness ratio SQ of a magnetic recording medium is large.

In an aspect, an M-type ferrite comprises an element Me comprising at least one of Ba, Sr, or Pb; an element Me′ comprising at least one of Ti, Zr, Ru, or Ir; and an element Me″ comprising at least one of In or Sc. In another aspect, a method of making the M-type ferrite can comprise milling ferrite precursor compounds comprising oxides of at least Co, Fe, Me, M3′, and Me″ to form an oxide mixture; wherein Me comprises at least one of Ba, Sr, or Pb; Me′ is at least one of Ti, Zr, Ru, or Ir; and Me″ is at least one of In or Sc; and calcining the oxide mixture in an oxygen or air atmosphere to form the ferrite.

A radio wave absorber film which is thin and exhibits excellent radio wave absorption performance; and a method for producing this radio wave absorber film. The radio wave absorber film formed on a base material layer contains a magnetic body and a binder resin in a radio wave absorption layer; and an aromatic ester-urethane copolymer is used as the binder resin. The glass transition temperature of the binder resin is 100° C. or less, and 0° C. or less. The magnetic body is at least one of an ε-iron oxide, a barium ferrite magnetic body and a strontium ferrite magnetic body

Some variations provide a magnetically anisotropic structure comprising a hexaferrite film disposed on a substrate, wherein the hexaferrite film contains a plurality of discrete and aligned magnetic hexaferrite particles, wherein the hexaferrite film is characterized by an average film thickness from about 1 micron to about 500 microns, and wherein the hexaferrite film contains less than 2 wt % organic matter. The hexaferrite film does not require a binder. Discrete particles are not sintered or annealed together because the maximum processing temperature to fabricate the structure is 500° C. or less, such as 250° C. or less. The magnetic hexaferrite particles may contain barium hexaferrite (BaFe.sub.12O.sub.19) and/or strontium hexaferrite (SrFe.sub.12O.sub.19). The hexaferrite film may be characterized by a remanence-to-saturation magnetization ratio of at least 0.7. Methods of making and using the magnetically anisotropic structure are also described.

The magnetic tape includes a non-magnetic support, a magnetic layer that includes ferromagnetic powder having an average particle volume of 2,500 nm.sup.3 or less on one surface side of the non-magnetic support, and a back coating layer that includes non-magnetic powder on the other surface side of the non-magnetic support, in which the ferromagnetic powder is ferromagnetic powder selected from the group consisting of hexagonal ferrite powder and ε-iron oxide powder, and a ratio (PSD.sub.5 μm-PSDmag/PSD.sub.10 μm-PSDbc) of the magnetic layer and the back coating layer is in a range of 0.0050 to 0.20. A magnetic tape cartridge and a magnetic recording and reproducing apparatus include the magnetic tape.

An electromagnetic wave absorbing particle has a composition, which is represented by Formula 1 of Sr.sub.1-xR.sub.xFe.sub.y-2zM.sub.2zO.sub.a and contains M-type hexaferrite as a main phase. In Formula 1, R is one or more substances selected from among Ba, Ca, and La, M is one or more substances selected from among Co, Ti, and Zr, 0<x≤0.8, 8≤y≤14, 0<z≤1.5, and a is equal to 19.

Disclosed herein are embodiments of an enhanced resonant frequency hexagonal ferrite material and methods of manufacturing. The hexagonal ferrite material can be Y-phase strontium hexagonal ferrite material. In some embodiments, sodium can be added into the crystal structure of the hexagonal ferrite material in order to achieve high resonance frequencies while maintaining high permeability.

Disclosed herein are embodiments of an enhanced resonant frequency hexagonal ferrite material, such as Y-phase hexagonal ferrite material, and methods of manufacturing. In some embodiments, sodium or potassium can be added into the crystal structure of the hexagonal ferrite material in order to achieve improved resonant frequencies in the range of 500 MHz to 1 GHz useful for radiofrequency applications.

Disclosed herein are embodiments of modified z-type hexagonal ferrite materials having improved properties that are advantageous for radiofrequency applications, in particular high frequency ranges for antennas and other devices. Atomic substitution of strontium, aluminum, potassium, and trivalent ions can be used to replace certain atoms in the ferrite crystal structure to improve loss factor at high frequencies.