Material coated with dispersion of ferromagnetic nanoparticles, and magnetic recording medium using the material

Abstract

Ferromagnetic nanoparticles which are produced by reducing, in the presence of a polymer, two or more metals having different reduction potentials twice or more, using two or more reducing agents having different reduction potentials, a material coated with a dispersion of ferromagnetic nanoparticles in which the ferromagnetic nanoparticles are dispersed, and a magnetic recording medium which has a magnetic layer consisting of the material. The ferromagnetic nanoparticles having a holding power Hc of 95.5 kA/m or more, the material coated with the dispersion of ferromagnetic nanoparticles having excellent industrial coatability, and the magnetic recording medium using the dispersion are provided.

What is claimed is:  
     
         1 . Ferromagnetic nanoparticles produced by reducing, in the presence of a polymer, at least two metals having different reduction potentials at least twice, using at least two reducing agents having different reduction potentials.  
     
     
         2 . The ferromagnetic nanoparticles of  claim 1 , wherein the at least two of the metals are a noble metal and a poor metal, and the noble metal is reduced before the poor metal.  
     
     
         3 . The ferromagnetic nanoparticles of  claim 2 , wherein the noble metal is reduced with a reducing agent having a reduction potential higher than −0.2 V and the poor metal is reduced with a reducing agent having a reduction potential lower than −0.2 V.  
     
     
         4 . The ferromagnetic nanoparticles of  claim 1 , wherein at least one of the metals is selected from the group consisting of Co, Fe, Ni, Mn, Cr, Pr, Pt, Au, Ag, Ir, and Rh.  
     
     
         5 . The ferromagnetic nanoparticles of  claim 2 , wherein at least one of the metals is selected from the group consisting of Co, Fe, Ni, Mn, Cr, Pr, Pt, Au, Ag, Ir, and Rh.  
     
     
         6 . The ferromagnetic nanoparticles of  claim 3 , wherein at least one of the metals is selected from the group consisting of Co, Fe, Ni, Mn, Cr, Pr, Pt, Au, Ag, Ir, and Rh.  
     
     
         7 . The ferromagnetic nanoparticles of  claim 1 , wherein the ferromagnetic nanoparticles are ferromagnetic regular alloys of CuAu or Cu 3 Au.  
     
     
         8 . The ferromagnetic nanoparticles of  claim 2 , wherein the ferromagnetic nanoparticles are ferromagnetic regular alloys of CuAu or Cu 3 Au.  
     
     
         9 . A material comprising a non-magnetic support coated with a dispersion containing at least ferromagnetic nanoparticles and a polymer, wherein the ferromagnetic particles are produced by reducing, in the presence of a polymer, at least two metals having different reduction potentials at least twice, using at least two reducing agents having different reduction potentials.  
     
     
         10 . The material of  claim 9 , wherein the at least two of the metals are a noble metal and a poor metal, and the noble metal is reduced before the poor metal.  
     
     
         11 . The material of  claim 10 , wherein the noble metal is reduced with a reducing agent having a reduction potential higher than −0.2 V and the poor metal is reduced with a reducing agent having a reduction potential lower than −0.2 V.  
     
     
         12 . The material of  claim 9 , wherein at least one of the metals is selected from the group consisting of Co, Fe, Ni, Mn, Cr, Pr, Pt, Au, Ag, Ir, and Rh.  
     
     
         13 . The material of  claim 9 , wherein the ferromagnetic nanoparticles are ferromagnetic regular alloys of CuAu or Cu 3 Au.  
     
     
         14 . The material of  claim 9 , wherein the material is formed by coating the dispersion onto the support and then annealing the coated support at a temperature that exceeds a transformation temperature between regular phase and irregular phase.  
     
     
         15 . A magnetic recording medium comprising a magnetic layer that consists of a material comprising a non-magnetic support coated with a dispersion containing at least ferromagnetic nanoparticles and a polymer, wherein the ferromagnetic nanoparticles are produced by reducing, in the presence of a polymer, at least two metals having different reduction potentials at least twice, using at least two reducing agents having different reduction potentials.  
     
     
         16 . The magnetic recording medium of  claim 15 , wherein at least two of the metals are a noble metal and a poor metal, and the noble metal is reduced before the poor metal.  
     
     
         17 . The magnetic recording medium of  claim 16 , wherein the noble metal is reduced with a reducing agent having a reduction potential higher than −0.2 V and the poor metal is reduced with a reducing agent having a reduction potential lower than −0.2 V.  
     
     
         18 . The magnetic recording medium of  claim 15 , wherein at least one of the metals is selected from the group consisting of Co, Fe, Ni, Mn, Cr, Pr, Pt, Au, Ag, Ir, and Rh.  
     
     
         19 . The magnetic recording medium of  claim 15 , wherein the ferromagnetic nanoparticles are ferromagnetic regular alloys of CuAu or Cu 3 Au.  
     
     
         20 . The magnetic recording medium of  claim 15 , wherein the material is formed by coating the dispersion onto the support and then annealing the coated support at a temperature that exceeds a transformation temperature between regular phase and irregular phase.