Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics

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Exchange bias in nanostructures

Magnetic Relaxation in Fine‐Particle Systems

In this feature article, the methods of obtaining various mesostructures made of nanocrystals are described. With silver and silver sulfide, the nanocrystals are able to self organize in 2D and 3D super lattices to form “supra” crystals. With cobalt and ferrites nanocrystals, it has been possible to make ribbons, dots, or labyrinths. These mesostructures present new physical properties differing from those of the isolated nanocrystal and from those of the bulk phase. Collective optical, magnetic, and transport properties are demonstrated. By applying a magnetic field during the deposition process of nanocrystals, the easy axes of the particles are oriented along the direction of the applied field, inducing again the collective magnetic properties.

Nanocrystal Self-Assemblies: Fabrication and Collective Properties

Fine hexaferrite particles for perpendicular recording prepared by the coprecipitation method in the presence of an inert component

The authors give the chemical, morphological, crystallographic, and magnetic properties of solid solutions between cubic iron sesquioxide γFe 2 O 3 and cobalt ferrite CoFe 2 O 4 obtained as fine particles by a new preparation method. This method gives the whole range of compositions and allows shifting of the magnetic and morphological features in a direction suitable for magnetic recording applications.

A contribution to the investigation of fine-particle solid solutions between cubic iron sesquioxide &#947;Fe 2 O 3 and cobalt ferrite CoFe 2 O 4

Specific magnetization of fine particles (γFe2O3, CoFe2O4) has been measured at 4.2 K in high magnetic fields. Saturation magnetization decreased linearly with increasing surfaces of particles.

Surface effects on saturation magnetization of fine spinel ferrite particles

Directional ordering has been shown to increase the magnetic performance of magnetic recording particles. The results obtained on new materials synthesized to investigate and to use directional order (DO) effects are presented. These materials, spinel defect ferrites, contain cations in several valence states (Fe/sup 2+/, Fe/sup 3+/, Mn/sup 2+/, Mn/sup 3+/, Mn/sup 4+/). Results of structural analysis and the influence of the oxidation state and thermal treatment on the magnetic properties are discussed. It is concluded that mixed defect spinel ferrites substituted by high-valence-state manganese ions (3+, 4+) and cobalt make it possible to obtain very high coercivities for low cobalt content (4.5%). Moreover, these materials present no aging effect. The extensive increase of the coercivity is due to the induced anisotropy by DO. The experimental results are interpreted according to the Neel model. >

Structure and induced anisotropy of new cobalt and manganese spinel defect ferrites

Iron-alumina nanocomposite powders containing 10 wt % iron were prepared by selective reduction of alumina-haematite solid solutions Microstructural study showed three types of metal dispersion in the alumina matrix according to the elaboration process: iron grains that were >70 nm, most of the iron particles were <10 nm and directly epitaxied in the alumina matrix, and iron particles that were surrounded by an interfacial phase In agreement with transmission electron miscroscopy (TEM) observations, magnetic study confirmed a distribution of the iron particles size, showing the superposition of a ferromagnetic behaviour (larger particles) and a superantiferromagnetic behaviour (smaller particles) Furthermore, analysis of thermoremanent behaviour, coercive field and dissymmetry of hysteresis loops allowed the interfacial phase surrounding some iron particles to be identified as an antiferromagnetic phase, Fe1+xAl2−xO4 Nevertheless, at the interface of metallic iron epitaxied on the alumina matrix some atomic planes always existed where iron was ionic (even if no other phase was detected) As a consequence the mean magnetic moment of iron in these nanocrystals is larger than that in bulk metallic iron

Paul Mollard

Papers

Fine hexaferrite particles for perpendicular recording prepared by the coprecipitation method in the presence of an inert component

A contribution to the investigation of fine-particle solid solutions between cubic iron sesquioxide γFe 2 O 3 and cobalt ferrite CoFe 2 O 4

Surface effects on saturation magnetization of fine spinel ferrite particles

Structure and induced anisotropy of new cobalt and manganese spinel defect ferrites

Microstructural and magnetic characterization of alumina-iron nanocomposites

Paul Mollard

Papers

Fine hexaferrite particles for perpendicular recording prepared by the coprecipitation method in the presence of an inert component

A contribution to the investigation of fine-particle solid solutions between cubic iron sesquioxide &#947;Fe 2 O 3 and cobalt ferrite CoFe 2 O 4

Surface effects on saturation magnetization of fine spinel ferrite particles

Structure and induced anisotropy of new cobalt and manganese spinel defect ferrites

Microstructural and magnetic characterization of alumina-iron nanocomposites

A contribution to the investigation of fine-particle solid solutions between cubic iron sesquioxide γFe 2 O 3 and cobalt ferrite CoFe 2 O 4