Abstract: Spindle-shaped magnetic metal particles containing iron as a main component, having an average major axis diameter (L) of 0.05 to 0.15 &mgr;m; a coercive force of 111.4 to 159.2 kA/m; a Co content of from 5 to less than 15 atm % based on whole Fe; a crystallite size of from 150 to less than 170 Å; a ratio of Al to Co from 0.3:1 to less than 2.0:1; a specific surface area (S) represented by the formula: S≦−160×L+65; an oxidation stability (&Dgr;&sgr;s) of saturation magnetization of not more than 4.5%; and an ignition temperature of not less than 145° C. The spindle-shaped magnetic metal particles containing iron as a main component, exhibit an adequate coercive force, and are excellent in dispersibility, oxidation stability and coercive force distribution despite fine particles, especially notwithstanding the particles have an average major axis diameter as small as 0.05 to 0.15 &mgr;m.

Abstract: Secondary agglomerates of magnetic metal particles for magnetic recording, have a sodium content of not more than 20 ppm and a calcium content of not more than 40 ppm, an average particle diameter of 300 to 800 &mgr;m and an upper limit of particle diameters of 2,000 &mgr;m, and comprise magnetic metal primary particles having an average major axis diameter of 0.05 to 0.25 &mgr;m.

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 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 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 are disclosed, which contain not less than 0.5 and less than 8 atom % of Co based on the total Fe and 5 to 10 atom % of Al based on the total Fe, and have an average major axis diameter of 0.18 to 0.30 &mgr;m, a size distribution (standard deviation/major axis diameter) of not more than 0.22, an average minor axis diameter of 0.025 to 0.045 &mgr;m and an average aspect ratio is 5 to 10. Spindle-shaped hematite particles and spindle-shaped magnetic iron-based alloy particles are also disclosed, which are produced from the above goethite particles. The spindle-shaped goethite particles of the present invention provide spindle-shaped magnetic iron-based alloy particles which are excellent in dispersibility (high squareness and high orientation), excellent both in weatherability and in coercive force distribution, and are useful as household DAT, 8 mm, Hi-8 tapes, VTR tapes for business purposes, computer tapes or floppy disks.

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: The present invention relates to spindle-shaped goethite particles having an average major axial diameter of 0.05 to 0.18 &mgr;m, spindle-shaped hematite particles having an average major axial diameter of 0.05 to 0.17 &mgr;m, spindle-shaped magnetic metal particles containing iron as a main component, which exhibit an adequate coercive force, good dispersibility, good oxidation stability and excellent coercive force distribution notwithstanding the average major axial diameter thereof is as small as 0.05 to 0.15 &mgr;m, and processes for producing the respective particles. Especially, the spindle-shaped magnetic metal particles containing iron as a main component, have an average major axial diameter of 0.05 to 0.15 &mgr;m, an aspect ratio of from 5:1 to 9:1, a size distribution (standard deviation/average major axial diameter) of not more than 0.30, a crystallite size D110 of 130 to 160 Å, a Co content of from 0.

Abstract: Secondary agglomerates of magnetic metal particles containing primary particles having an average major axial diameter of 0.05 to 0.25 &mgr;m, said secondary agglomerates having an average particle diameter of 300 to 800 &mgr;m, an upper limit of particle diameter of 2,000 &mgr;m and a repose angle of 38 to 45°. The secondary agglomerates exhibit not only excellent handing property due to high storage efficiency, high transport efficiency and good flowability thereof, but also excellent kneading property when kneaded with various binder resins and organic solvents in a kneader, and excellent dilution-dispersibility when diluted with an additional amount of the organic solvent, upon the production of coating-type magnetic recording media, so as to more improve a surface smoothness and squareness of a magnetic coating film obtained therefrom, and a process for producing such secondary agglomerates of magnetic metal particles for magnetic recording.

Abstract: Spindle-shaped goethite particles of the present invention uniformly contain cobalt of 1 to 20 atm %, calculated as Co, based on whole Fe and aluminum of 1 to 15 atm %, calculated as Al, based on whole Fe, and have an X-ray crystallite size ratio (D020:D110) of not less than 1.0:1 and less than 2.0:1, an average major axial diameter of 0.05 to 0.20 &mgr;m, an average minor axial diameter of 0.010 to 0.020 &mgr;m and an average aspect ratio (average major axial diameter:average minor axial diameter) of 4:1 to 10:1.

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 present invention relates to a spindle-shaped goethite particles containing cobalt of 8.0 to 50.0 atm %, calculated as Co, based on the total Fe in the spindle-shaped goethite particles and a compound of at least one element selected from the group consisting of Al, Si, Nd, Y, La, Ce, Pr, Tb, Ca, Mg, Ba and Sr of not more than 25.0 atm %, calculated as the element, based on the total Fe in the spindle-shaped goethite particles, and having an average major axis diameter of 0.05 to 0.15 .mu.m, a size distribution (standard deviation/major axis diameter) of not more than 0.30, an average minor axis diameter of 0.010 to 0.025 .mu.m, an aspect ratio of 4 to 8 and an X-ray crystallite size ratio (D.sub.020 /D.sub.110) of 2.0 to 3.5.

Abstract: The disclosure describes spindle-shaped magnetic iron-based alloy particles containing cobalt and iron as the main ingredients in which the Co content is 1.0 to 50.0 atm % (calculated as Co) based on the total Fe in the spindle-shaped magnetic iron-based alloy particles, and which the spindle-shaped magnetic iron-based alloy particles have an average major axis diameter of 0.05 to 0.18 .mu.m, a size distribution (standard deviation/major axis diameter) of not more than 0.25, an average minor axis diameter of 0.010 to 0.020 .mu.m, an aspect ratio (major axis diameter/minor axis diameter) of 4 to 15, an X-ray crystallite size D.sub.110 of 120 to 180 .ANG., a coercive force of 1720 to 2500 Oe, a saturation magnetization of not less than 110 emu/g, and a saturation magnetization decrement percentage of not more than 17%.

Abstract: The present invention is a method for making highly stable magnetic alloy particles with high coercivities and high saturation magnetization comprising the steps of:a) providing a precursor selected from the group consisting of iron oxide hydroxide particles and iron oxide particles, wherein the precursor particle comprises from about 15 to about 45 atomic % Co based on amount of Fe present,b) reducing the precursor particles to magnetic alloy particles,c) passivating the magnetic alloy particles in an oxygen-containing atmosphere at a temperature between about 20.degree. and 100.degree. C.,d) annealing the passivated magnetic alloy particles in an inert atmosphere at a temperature from about 120.degree. to about 450.degree. C., ande) further oxidizing the annealed magnetic alloy particles in an oxygen-containing atmosphere.

Abstract: The disclosure describes spindle-shaped magnetic iron-based alloy particles containing cobalt and iron as the main ingredients in which the Co content is 1.0 to 50.0 atm % (calculated as Co) based on the total Fe in the spindle-shaped magnetic iron-based alloy particles, and which the spindle-shaped magnetic iron-based alloy particles have an average major axis diameter of 0.05 to 0.18 .mu.m, a size distribution (standard deviation/major axis diameter) of not more than 0.25, an average minor axis diameter of 0.010 to 0.020 .mu.m, an aspect ratio (major axis diameter/minor axis diameter) of 4 to 15, an X-ray crystallite size D.sub.110 of 120 to 180 .ANG., a coercive force of 1720 to 2500 Oe, a saturation magnetization of not less than 110 emu/g, and a saturation magnetization decrement percentage of not more than 17%.

Abstract: Disclosed herein are spindle-shaped magnetic iron based alloy particles containing at least one selected from the group consisting of Ni, Al, Si, P, Co, Mg, B and Zn, which have a particle length of 0.05 to 0.40 .mu.m, a crystallite size of 110 to 180 .ANG., a specific surface area of 30 to 60 m.sup.2 /g, a coercive force of 1,300 to 1,700 Oe and a saturation magnetization (.sigma.s) of not less than 100 emu/g and a process for producing the same.

Abstract: Disclosed herein are granulated particles for magnetic particles for magnetic recording, comprising: acicular ferric hydroxide oxide particles or acicular iron oxide particles; and at least one selected from the group consisting of semisynthetic starch and semisynthetic cellulose and having a bulk density of not less than 0.3 g/cm.sup.3 and a powdering ratio of not more than 40%, and a process for producing the granulated particles, and magnetic particles obtained from such granulated particles.

Abstract: Disclosed herein are spindle-shaped magnetic iron based alloy particles containing at least one selected from the group consisting of Ni, Al, Si, P, Co, Mg, B and Zn, which have a particle length of 0.05 to 0.40 .mu.m, a crystallite size of 110 to 180 .ANG., a specific surface area of 30 to 60 m.sup.2 /g, a coercive force of 1,300 to 1,700 Oe and a saturation magnetization (.sigma.s) of not less than 100 emu/g and a process for producing the same.

Abstract: Disclosed herein are acicular magnetic iron based alloy particles for magnetic recording, containing 1.5 to 10 mol % of B based on Fe (calculated as B) and 1.5 to 10 mol % of Co based on Fe (calculated as Co) in the vicinity of the surfaces of said particles and having a saturation magnetization of not less than 125 emu/g and an S.F.D. value of not more than 0.50, and a process for producing the same.

Abstract: Disclosed herein are acicular magnetic iron based alloy particles for magnetic recording, containing 1.5 to 10 mol % of B based on Fe (calculated as B) and 1.5 to 10 mol % of Co based on Fe (calculated as Co) in the vicinity of the surfaces of said particles and having a saturation magnetization of not less than 125 emu/g and an S.F.D. value of not more than 0.50, and a process for producing the same.