A soft magnetic alloy or the like combining high saturated magnetic flux density, low coercive force and high magnetic permeability μ′ having the composition formula (Fe.sub.(1−(α+β))X1.sub.αX2.sub.β).sub.(1−(a+b+c+d+e))B.sub.aSi.sub.bC.sub.cCu.sub.dM.sub.e. X1 is one more elements selected from the group consisting of Co and Ni, X2 is one or more elements selected from the group consisting of Al, Mn, Ag, Zn, Sn, As, Sb, Bi, N, O and rare earth elements, and M is one or more elements selected from the group consisting of Nb, Hf, Zr, Ta, Ti, Mo, W and V. 0.140<a≤0.240, 0≤b≤0.030, 0<c<0.080, 0<d≤0.020, 0≤e≤0.030, α≥0, β≥0, and 0≤α+β≤0.50 are satisfied.

A soft magnetic alloy or the like combining high saturated magnetic flux density, low coercive force and high magnetic permeability μ′ having the composition formula (Fe.sub.(1−(α+β))X1.sub.αX2.sub.β).sub.(1−(a+b+c+d+e))B.sub.aSi.sub.bC.sub.cCu.sub.dM.sub.e. X1 is one more elements selected from the group consisting of Co and Ni, X2 is one or more elements selected from the group consisting of Al, Mn, Ag, Zn, Sn, As, Sb, Bi, N, O and rare earth elements, and M is one or more elements selected from the group consisting of Nb, Hf, Zr, Ta, Ti, Mo, W and V. 0.140<a≤0.240, 0≤b≤0.030, 0<c<0.080, 0<d≤0.020, 0≤e≤0.030, α≥0, β≥0, and 0≤α+β≤0.50 are satisfied.

To obtain a magnetic core having an improved withstand voltage property while maintaining a high relative magnetic permeability, and the like. The magnetic core contains large particles observed as soft magnetic particles having a Heywood diameter of 5 μm or more and 25 μm or less and small particles observed as soft magnetic particles having a Heywood diameter of 0.5 μm or more and less than 5 μm in a cross section. C1<C2 is satisfied in which an average circularity of the small particles close to the large particles is C1 and an average circularity of all small particles observed in the cross section including small particles not close to the large particles is C2. The small particles close to the large particles are defined as small particles whose distance from centroids of the small particles to a surface of the large particles is 3 μm or less.

Provided is a soft magnetic alloy which has high saturation flux density and low coercivity and is represented by the compositional formula (Fe.sub.(1−(α+β))X1.sub.αX2.sub.β).sub.(1−(a+b+c+d+e+f))M.sub.aP.sub.bSi.sub.cCu.sub.dX3.sub.eB.sub.f, wherein X1 is at least one element selected from the group consisting of Co and Ni, X2 is at least one element selected from the group consisting of Ti, V, Mn, Ag, Zn, Al, Sn, As, Sb, Bi, and rare earth elements, X3 is at least one element selected from the group consisting of C and Ge, and M is at least one element selected from the group consisting of Zr, Nb, Hf, Ta, Mo, and W, and wherein 0.030≤a≤0.120, 0.010≤b≤0.150, 0≤c≤0.050, 0≤d≤0.020, 0≤e≤0.100, 0≤f≤0.030, α≥0, β≥0, and 0≤α+β≤0.55.

A dust core includes a compact containing a soft magnetic powder and also includes a cover coat for the compact. The cover coat contains a polyamideimide-modified epoxy resin. An electric/electronic component includes the dust core, a coil, and a connection terminal connected to each end portion of the coil. At least one portion of the dust core is placed so as to be located in an induced magnetic field generated by the current flowing in the coil through the connection terminal. An electric/electronic device includes the electric/electronic component.

A soft magnetic metal powder includes a coated particle having a soft magnetic metal particle and a coating layer coating a surface of the soft magnetic metal particle. The coating layer contains at least one compound selected from the group consisting of molybdenum disulfide, molybdenum oxide, boron nitride, mica, talc, pyrophyllite, and kaolinite.

A magnetic piece, a multilayer magnetic piece and a multilayer core with an adhesive agent of excellent saturation magnetic flux density are provided. The magnetic piece includes a soft magnetic amorphous alloy ribbon 1 and a resin layer 2 provided on at least one surface of the soft magnetic amorphous alloy ribbon. The resin layer contains a resin whose Shore D hardness is not more than 60. The resin may have a Shore D hardness of not more than 25 or may have a Shore D hardness of not less than 1.

A soft magnetic alloy contains Fe and at least one of metalloid element. An amorphous material and a nanocrystal having a grain size of 5 to 30 nm are mixed. A coefficient of determination between an atomic concentration of Fe and an atomic concentration of the at least one of metalloid element is 0.700 or more.

A soft magnetic alloy contains Fe and at least one of metalloid element. An amorphous material and a nanocrystal having a grain size of 5 to 30 nm are mixed. A coefficient of determination between an atomic concentration of Fe and an atomic concentration of the at least one of metalloid element is 0.700 or more.

A magnetic bead reagent contains: a magnetic bead containing a Fe-based metal soft magnetic particle and a silica film that has an average thickness of 20 nm or more and that covers the Fe-based metal soft magnetic particle; a surfactant; and a dispersion medium in which the magnetic bead is dispersed. The surfactant may be a nonionic surfactant.