Abstract: The present invention relates to a process for producing magnetic metal particles for magnetic recording, comprising: heat-treating goethite particles having an aluminum content of 4 to 50 atom % in terms of Al based on whole Fe to obtain hematite particles; and heat-reducing the hematite particles at a temperature of 200 to 600° C., the goethite particles being obtained by adding a peroxodisulfate to a reaction solution comprising: a ferrous salt aqueous solution and a mixed alkali aqueous solution comprising: an alkali hydrogen carbonate aqueous solution or alkali carbonate aqueous solution and an alkali hydroxide aqueous solution before initiation of an oxidation reaction of the reaction solution, and then conducting the oxidation reaction.

Abstract: The present invention relates to ferromagnetic metal particles having an average major axis diameter (L) of 10 to 100 nm which satisfy a relationship between the average major axis diameter (L) and a particle SFD represented by the following formula: Particle SFD?0.0001 L2?0.0217 L+1.75; a process for producing the ferromagnetic metal particles; and a magnetic recording medium using the ferromagnetic metal particles.

Abstract: The present invention relates to ferromagnetic metal particles having a bulk density (?a) of not more than 0.25 g/cm3, a process for producing the above ferromagnetic metal particles and a magnetic recording medium comprising a non-magnetic substrate; a non-magnetic undercoat layer formed on the non-magnetic substrate which comprises non-magnetic particles and a binder resin; and a magnetic recording layer formed on the non-magnetic undercoat layer which comprises magnetic particles and a binder resin, wherein the above ferromagnetic metal particles were used as the magnetic particles.

Abstract: The present invention relates to a process for producing magnetic metal particles for magnetic recording, comprising: heat-treating goethite particles having an aluminum content of 4 to 50 atom % in terms of Al based on whole Fe to obtain hematite particles; and heat-reducing the hematite particles at a temperature of 200 to 600° C., the goethite particles being obtained by adding a peroxodisulfate to a reaction solution comprising: a ferrous salt aqueous solution and a mixed alkali aqueous solution comprising: an alkali hydrogen carbonate aqueous solution or alkali carbonate aqueous solution and an alkali hydroxide aqueous solution before initiation of an oxidation reaction of the reaction solution, and then conducting the oxidation reaction.

Abstract: Spherical tetragonal barium titanate particles of the present invention have a perovskite crystal structure, an average particle diameter of 0.05 to 0.5 ?m, a particle size distribution ?g of not less than 0.70, and a ratio of Ba to Ti of 0.99:1 to 1.01:1. The spherical tetragonal barium titanate particles exhibit an excellent dispersibility as well as a high denseness, a high purity and excellent permittivity properties.

Abstract: Spherical tetragonal barium titanate particles of the present invention have a perovskite crystal structure, an average particle diameter of 0.05 to 0.5 ?m, a particle size distribution ?g of not less than 0.70, and a ratio of Ba to Ti of 0.99:1 to 1.01:1. The spherical tetragonal barium titanate particles exhibit an excellent dispersibility as well as a high denseness, a high purity and excellent permittivity properties.

Abstract: Spherical tetragonal barium titanate particles of the present invention have a perovskite crystal structure, an average particle diameter of 0.05 to 0.5 &mgr;m, a particle size distribution &sgr;g of not less than 0.70, and a ratio of Ba to Ti of 0.99:1 to 1.01:1. The spherical tetragonal barium titanate particles exhibit an excellent dispersibility as well as a high denseness, a high purity and excellent permittivity properties.

Abstract: Spherical tetragonal barium titanate particles of the present invention have a perovskite crystal structure, an average particle diameter of 0.05 to 0.5 &mgr;m, a particle size distribution &sgr;g of not less than 0.70, and a ratio of Ba to Ti of 0.99:1 to 1.01:1. The spherical tetragonal barium titanate particles exhibit an excellent dispersibility as well as a high denseness, a high purity and excellent permittivity properties.

Abstract: A magnetic recording medium of the present invention comprises: a base film; a non-magnetic undercoat layer formed on said base film and comprising a binder resin and non-magnetic acicular particles containing iron as a main component, comprising iron and titanium of 0.05 to 50% by weight, calculated as Ti, based on the total weight of the particles, which is present within the particle; and a magnetic recording layer formed on said non-magnetic undercoat layer and comprising magnetic particles and a binder resin. Such a magnetic recording medium has a low light transmittance, an excellent smooth surface, a high mechanical strength and an excellent durability.

Abstract: Disclosed herein are non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium, comprising acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles coated with at least one selected from the group consisting of an A1 compound, a silane coupling agent, a titanate coupling agent, an aluminate coupling agent and a zirconate coupling agent; a non-magnetic undercoating layer containing such non-magnetic particles; and magnetic recording medium having such an undercoating layer.