Nanoparticle, method of producing nanoparticle and magnetic recording medium

A method of producing a plural type alloy nanoparticle, the method comprising producing a nanoparticle made of a plural type alloy through a reducing step of mixing one or more reverse micelle solutions (I) containing a metal salt with a reverse micelle solution (II) containing a reducing agent to carry out reducing treatment and a maturing step of carrying out maturing treatment after the reducing treatment, wherein

• at least two metals constituting the plural type alloy are selected from the VIb group and VIII group in the periodic table;
• and
• at least one metal constituting the plural type alloy is selected from the group consisting of Cu, Ag, B, In, Sn, Pb, P, Sb and Bi and the content of these selected metals is 1 to 30 at. % of all of the plural type alloy, wherein
• the ratio (water/surfactant) by mass of water to a surfactant in each of the reverse micelle solutions (I) and (II) is 20 or less;
• the reducing reaction temperature is constant in the range from −5 to 30° C.;
• the maturing temperature is higher than the reducing reaction temperature and is constant in a range from 30 to 90° C., and the maturing time is 5 to 180 minutes.