Abstract: Magnetic metal particles containing iron as a main component, comprising cobalt in an amount of usually 20 to 50 atm %, calculated as Co, based on whole Fe, aluminum in an amount of usually 3 to 15 atm %, calculated as Al, based on whole Fe and a rare earth element in an amount of usually 3 to 20 atm %, calculated as rare earth element, based on whole Fe, and having an average major axis diameter of usually 0.02 to 0.065 ?m, preferably from 0.02 to less than 0.05 ?m, a coercive force of usually 159.2 to 222.9 kA/m (2,000 to 2,800 Oe), a soluble Na content of usually not more than 30 ppm, a soluble Ca content of usually not more than 100 ppm, and an oxidation stability ??s of usually not more than 10%.

Abstract: A perpendicular magnetic recording medium, comprises a substrate; a soft-magnetic layer formed on the substrate; an NaCl-type oxide layer for orientation control formed on the soft-magnetic layer, having a thickness of from more than 0 to less than 10 nm; and a magnetic recording layer formed on the NaCl-type oxide layer for orientation control, comprising a maghemite thin film. Such a perpendicular magnetic recording medium is capable of showing excellent magnetic properties, a high recording resolution and improved surface properties.

Abstract: A magnetic recording medium exhibiting a high coercive force and excellent squareness having a substrate, an underlayer formed on the substrate, and a spinel-type iron oxide thin film with maghemite as a main component formed on the underlayer. The spinel-type iron oxide thin film has a thickness (t) of 5 to 50 nm, is constituted by grains having an average grain size (D) of 5 to 30 nm, standard deviation of sizes of grain of not more than 4 nm and a ratio (D/t) of the average grain size (D) to the thickness (t) of less than 1.0, exhibits a coercive force of not less than 159 kA/m (2,000 Oe) and a coercive squareness ratio S* of not less than 0.5:1 in a longitudinal recording medium or a squareness ratio not less than 0.75:1 in a perpendicular recording medium.

Abstract: Spindle-shaped magnetic alloy particles containing Fe and Co as main components of the present invention have a cobalt content of 20 to 50 atm % (calculated as Co) based on whole Fe; an average major axis diameter (L) of 0.03 to 0.10 &mgr;m; a coercive force value of 159.2 to 238.7 kA/m (2,000 to 3,000 Oe); a crystallite size of 100 to 160 Å; and an activation volume (Vact) of 0.01 to 0.07E-4 &mgr;m3. A high-density magnetic recording medium produced by using such spindle-shaped magnetic alloy particles containing Fe and Co as main components, have an excellent output characteristics in a short wavelength region, a considerably reduced noise and an excellent storage stability.

Abstract: The silica gel carrying a titanium oxide photocatalyst in a high concentration of the present invention is characterized in that the concentration of the titanium oxide contained in the pores near the surface of the silica gel is 7-70% by weight, said silica gel having an average pore diameter of 6-100 nm, provided that the concentration gradient is provided such that the amount of the titanium oxide contained in the pores near the surface of the silica gel is 1.5 times or more than the amount of the titanium oxide contained in the pores near the central part of the silica gel.

Abstract: A perpendicular magnetic recording medium, comprises a substrate; a soft-magnetic layer formed on the substrate; an NaCl-type oxide layer for orientation control formed on the soft-magnetic layer, having a thickness of from more than 0 to less than 10 nm; and a magnetic recording layer formed on the NaCl-type oxide layer for orientation control, comprising a maghemite thin film. Such a perpendicular magnetic recording medium is capable of showing excellent magnetic properties, a high recording resolution and improved surface properties.

Abstract: Magnetic metal particles containing iron as a main component, comprising cobalt in an amount of usually 20 to 50 atm %, calculated as Co, based on whole Fe, aluminum in an amount of usually 3 to 15 atm %, calculated as Al, based on whole Fe and a rare earth element in an amount of usually 3 to 20 atm %, calculated as rare earth element, based on whole Fe, and having an average major axis diameter of usually 0.02 to 0.065 &mgr;m, preferably from 0.02 to less than 0.05 &mgr;m, a coercive force of usually 159.2 to 222.9 kA/m (2,000 to 2,800 Oe), a soluble Na content of usually not more than 30 ppm, a soluble Ca content of usually not more than 100 ppm, and an oxidation stability &Dgr;&sgr;s of usually not more than 10%.

Abstract: A magnetic recording medium, comprising: a substrate; an underlayer formed on the substrate; and a spinel-type iron oxide thin film comprising maghemite as a main component formed on the underlayer,

Abstract: Spindle-shaped goethite particles of the present invention contain Co of 8 to 45 atm %, calculated as Co, based on whole Fe, Al of 5 to 20 atm %, calculated as Al, based on whole Fe, and have an average major axial diameter of 0.05 to 0.18 &mgr;m, each of said spindle-shaped goethite particles comprising a seed portion and a surface layer portion, the weight ratio of said seed portion to said surface layer portion being 30:70 to 80:20 and the relationship of the Co concentration of the seed portion with that of the hematite particle being 50 to 95:100 when the Co concentration of the hematite particle is 100, and said Al existing in said surface layer portion. Such spindle-shaped goethite particles are fine particles and exhibit a good particle size distribution.

Abstract: Spindle-shaped magnetic alloy particles containing Fe and Co as main components of the present invention have a cobalt content of 20 to 50 atm% (calculated as Co) based on whole Fe; an average major axis diameter (L) of 0.03 to 0.10 &mgr;m; a coercive force value of 159.2 to 238.7 kA/m (2,000 to 3,000 Oe); a crystallite size of 100 to 160 Å; and an activation volume (Vact) of 0.01 to 0.07E-4 &mgr;m3. A high-density magnetic recording medium produced by using such spindle-shaped magnetic alloy particles containing Fe and Co as main components, have an excellent output characteristics in a short wavelength region, a considerably reduced noise and an excellent storage stability.

Abstract: Spindle-shaped hematite particles obtained form the spindle-shaped goethite particles, can be prevented as highly as possible from causing destruction of particle shape when subjected to a heat-reduction step for producing magnetic spindle-shaped metal particles and magnetic spindle-shaped metal particles containing iron as a main component produced from the spindle-shaped goethite particles or the spindle-shaped hematite particles as a starting material, exhibit a high coercive force, an excellent particle coercive force distribution, a large saturation magnetization and an excellent oxidation stability, and are excellent in a squareness (Br/Bm) of the sheet due to a good dispersibility in a binder resin.

Abstract: Spindle-shaped goethite particles of the present invention contain Co of 8 to 45 atm %, calculated as Co, based on whole Fe, Al of 5 to 20 atm %, calculated as Al, based on whole Fe, and have an average major axial diameter of 0.05 to 0.18 &mgr;m, each of said spindle-shaped goethite particles comprising a seed portion and a surface layer portion, the weight ratio of said seed portion to said surface layer portion being 30:70 to 80:20 and the relationship of the Co concentration of the seed portion with that of the hematite particle being 50 to 95:100 when the Co concentration of the hematite particle is 100, and said Al existing in said surface layer portion. Such spindle-shaped goethite particles are fine particles and exhibit a good particle size distribution.

Abstract: Spindle-shaped metal particles and a process for producing magnetic spindle-shaped metal particle containing iron as a main component, which contains cobalt of 8 to 45 atm % calculated as Co, aluminum of 5 to 20 atm %, calculated as Al, and a rare earth element of 1 to 15 atm %, calculated as rare earth element, wherein the particles have an average major axial diameter of 0.05 to 0.15 &mgr;m, an average minor axial diameter of 0.010 to 0.022 &mgr;m, an aspect ratio of 4:1 to 8:1, a particle size distribution of not more than 0.20, and an X-ray crystallite size D110 of 12.0 to 17.0 nm. The spindle-shaped metal particles have a high coercive force, an excellent particle coercive force distribution, a large saturation magnetization and an excellent oxidation stability, and are excellent in a squareness (Br/Bm) of the sheet due to a good dispersibility in a binder resin.

Abstract: The disclosure describes a non-magnetic undercoating layer for a magnetic recording medium, coated on the surface of a non-magnetic substrate comprising:non-magnetic particles selected from the group consisting of particles (1) and (2):(1) coated acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles which are produced by adhering not less than 0.01 to 20 wt % (calculated as Al, SiO.sub.2 or Al and SiO.sub.2, and based on acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles as a core material) of an oxide or a hydroxide containing Al, Si or both Al and Si to the surfaces of acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles as a core material, and have a molecular weight-dependent parameter .alpha. represented by the following formula of not less than 0.5:As=K.sub.1 .multidot.M.sup..alpha.wherein M represents the number-average molecular weight of a binder resin, As represents the saturation adsorption of said binder resin, and K.sub.

Abstract: The disclosure describes a non-magnetic undercoating layer for a magnetic recording medium, coated on the surface of a non-magnetic substrate comprising:non-magnetic particles selected from the group consisting of particles (1) and (2):(1) coated acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles which are produced by adhering not less than 0.01 to 20 wt % (calculated as Al, SiO.sub.2 or Al and SiO.sub.2, and based on acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles as a core material) of an oxide or a hydroxide containing Al, Si or both Al and Si to the surfaces of acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles as a core material, and have a molecular weight-dependent parameter .alpha. represented by the following formula of not less than 0.5:As=K.sub.1 .multidot.M.sup..alpha.wherein M represents the number-average molecular weight of a binder resin, As represents the saturation adsorption of said binder resin, and K.sub.

Abstract: The disclosure describes a non-magnetic undercoating layer for a magnetic recording medium, coated on the surface of a non-magnetic substrate comprising:non-magnetic particles selected from the group consisting of particles (1) and (2):(1) coated acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles which are produced by adhering not less than 0.01 to 20 wt % (calculated as Al, SiO.sub.2 or Al and SiO.sub.2, and based on acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles as a core material) of an oxide or a hydroxide containing Al, Si or both Al and Si to the surfaces of acicular or spindle-shaped .alpha.-Fe.sub.2 O.sub.3 particles as a core material, and have a molecular weight-dependent parameter .alpha. represented by the following formula of not less than 0.5:As=K.sub.1 .multidot.M.sup..alpha.wherein M represents the number-average molecular weight of a binder resin, As represents the saturation adsorption of said binder resin, and K.sub.

Abstract: Disclosed herein are plate-like composite Ba-containing ferrite fine particles for magnetic recording, containing Ni, Co and Ti in the molar ratios defined by 0.02.ltoreq.Ni/Fe.ltoreq.0.10, 0.01.ltoreq.Co/Fe.ltoreq.0.10 and 0.01.ltoreq.Ti/Fe.ltoreq.0.10, but 0.03.ltoreq.(Ni+Co)/Fe.ltoreq.0.14 and Ti/(Ni+Co)<1, and having zinc in the vicinity of the particle surface in the form of solid solution, and a temperature dependence of coercive force of said particles in the range of -0.5 to +2.0 Oe/.degree.C. in the temperature range of -20.degree. to 120.degree. C., and a process for producing the same.

Abstract: Disclosed herein are plate-like composite ferrite fine particles for magnetic recording comprising plate-like composite ferrite containing Ba fine particles which contain Ti of 2 to 5.0 atomic % based on Fe.sup.3+ and Ni in the range of 1.2.ltoreq.Ni/Ti.ltoreq.4 by molar ratio, which have zinc in the vicinity of the particles surfaces in the form of a solid solution, which have an average particle diameter of 0.01 .mu.m to 0.08 .mu.m, and the coercive force of which scarcely varies with the rise in temperature in the temperature range of -20.degree. C. to 120.degree. C., and a process for producing such plate-like composite ferrite fine particles.