BACKGROUND

This disclosure is directed to grain-oriented M-type hexagonal ferrites that have high permeability and low magnetic loss over a broad range of operating frequencies.

Spinel and hexagonal ferrites have considerable potential for use in a variety of low-profile electronic devices, such as perpendicular magnetic records, antennas, microwave absorbers, and electromagnetic interference suppressors. With the increasing market in microwave communications, the magnetic and microwave properties of ferrite compacts or films can be tailored to meet the requirements of diverse applications.

High permeability and low magnetic loss at microwave frequencies will provide materials for the creation of electrically small antennas for electronic communications. The unique magnetodielectric nature of ferrite substrates allows for miniaturization of antenna elements without the subsequent loss of bandwidth that is often observed in high dielectric constant substrates. Magnetodielectric materials thus have great potential for application in the miniaturization of antennas with broad bandwidth, which are widely used in personal mobile phones, base stations, and the like. For example, both microwave antennas and inductors are vital components in advanced microwave communications.

What is needed are novel ferrites with magnetodielectric properties suitable for microwave communication applications and others.

BRIEF SUMMARY

In an aspect, a grain-oriented M-type hexagonal ferrite has the formula
MeFe12O19,
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+, Ba2+or Pb2+, and wherein greater than 30%, preferably greater than 80%, of c-axes of the ferrite grains are aligned perpendicular to the c-plane.

In another aspect, included are articles comprising the grain-oriented M-type hexagonal ferrite.

In yet another aspect, a method of making a doped, grain-oriented M-type hexagonal ferrite comprises preparing a plurality of ferrite grains of the formula
MeFe12O19
comprising a dopant effective to provide planar magnetic anisotropy and easy magnetization in a c-plane, or a cone anisotropy, wherein Me is Sr+, Ba2+, or Pb2+; aligning the plurality of ferrite grains such that greater than 30%, preferably greater than 80% of the c-axes of the ferrite grains are aligned 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., preferably 800-1350° C. to provide a sintered material having a density of at least 85% of a theoretical density, preferably greater than 90% of a theoretical density.

The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description and appended claims.

