A ferrite sintered magnet contains a main phase formed of ferrite having a hexagonal magnetoplumbite type crystalline structure; a first subphase containing La, Ca, and Fe, in which an atomic ratio of La is higher than that of the main phase, and the atomic ratio of La is higher than an atomic ratio of Ca; and a second subphase containing La, Ca, Si, B, and Fe, in which an atomic ratio of Ca is higher than an atomic ratio of La, an atomic ratio of B is higher than an atomic ratio of Fe, and the atomic ratio of Fe is lower than that of the main phase. An area ratio of the second subphase on a cross-sectional surface of the ferrite sintered magnet is greater than or equal to 1%.

A ferrite sintered magnet contains a main phase formed of ferrite having a hexagonal magnetoplumbite type crystalline structure; a first subphase containing La, Ca, and Fe, in which an atomic ratio of La is higher than that of the main phase, and the atomic ratio of La is higher than an atomic ratio of Ca; and a second subphase containing La, Ca, Si, B, and Fe, in which an atomic ratio of Ca is higher than an atomic ratio of La, an atomic ratio of B is higher than an atomic ratio of Fe, and the atomic ratio of Fe is lower than that of the main phase. An area ratio of the second subphase on a cross-sectional surface of the ferrite sintered magnet is greater than or equal to 1%.

Provided are magnetic particles (cobalt ferrite) having a micrometer-order average particle diameter and similar particle diameters. A cobalt ferrite precursor is heated in the presence of a sulfite, thereby obtaining intended cobalt ferrite magnetic particles.

Provided are magnetic particles (cobalt ferrite) having a micrometer-order average particle diameter and similar particle diameters. A cobalt ferrite precursor is heated in the presence of a sulfite, thereby obtaining intended cobalt ferrite magnetic particles.

Provided is an ε-iron oxide type ferromagnetic powder with a powder pH within a range of 4.8 to 6.8; and a method for manufacturing the ε-iron oxide type ferromagnetic powder and a composition containing at least the ε-iron oxide type ferromagnetic powder and a solvent.

Provided is an ε-iron oxide type ferromagnetic powder with a powder pH within a range of 4.8 to 6.8; and a method for manufacturing the ε-iron oxide type ferromagnetic powder and a composition containing at least the ε-iron oxide type ferromagnetic powder and a solvent.

The invention provides a core-shell particle which can provide, by being calcinated, epsilon type iron oxide-based compound particles that have a small coefficient of variation of primary particle diameter and show excellent SNR and running durability when employed in a magnetic recording medium as well as applications thereof. The core-shell particle includes: a core including at least one iron oxide selected from Fe.sub.2O.sub.3 or Fe.sub.3O.sub.4, or iron oxyhydroxide; and a shell that coats the core, the shell including a polycondensate of a metal alkoxide and a metal element other than iron, as well as applications thereof.

The invention provides a core-shell particle which can provide, by being calcinated, epsilon type iron oxide-based compound particles that have a small coefficient of variation of primary particle diameter and show excellent SNR and running durability when employed in a magnetic recording medium as well as applications thereof. The core-shell particle includes: a core including at least one iron oxide selected from Fe.sub.2O.sub.3 or Fe.sub.3O.sub.4, or iron oxyhydroxide; and a shell that coats the core, the shell including a polycondensate of a metal alkoxide and a metal element other than iron, as well as applications thereof.

A substituted ε-iron oxide magnetic particle powder having a reduced content of an α-type iron-based oxide and Fe sites of ε-Fe.sub.2O.sub.3 partially substituted by another metal element is obtained by neutralizing an acidic aqueous solution containing a trivalent iron ion and an ion of a metal that partially substitutes Fe sites to a pH of between 2.0 and 7.0. Thereafter, a silicon compound having a hydrolyzable group is added to a dispersion liquid containing an iron oxyhydroxide having a substituent metal element or a mixture of an iron oxyhydroxide and a hydroxide of a substituent metal element. The dispersion liquid is neutralized to a pH of 8.0 or higher and the iron oxyhydroxide having a substituent metal element or the mixture of the iron oxyhydroxide and the hydroxide of a substituent metal element is coated with a chemical reaction product of the silicon compound. The dispersion is then heated.

The present invention provides a composition comprising a plurality of magnetic nanocomposite particles. The magnetic nanocomposite particle comprises a magnetic metallic nanoparticle and a plurality of organic polymer ligands attached to its surface. The composition can also include a host matrix, such as a polymer, in which the magnetic nanocomposite particles are interspersed therein. The compositions of the invention have the Verdet constant of at least 5000°/T-m.