According to an aspect, a soft magnetic metal powder includes a plurality of soft magnetic metal particles containing iron, a surface of each of the soft magnetic metal particles is covered with a coating part, and a maximum height Sz of a surface of the coating part is 10 to 700 nm. According to another aspect, a soft magnetic metal powder includes a plurality of soft magnetic metal particles containing iron, a surface of each of the soft magnetic metal particles is covered with a coating part, and a maximum height Rz of a surface of the coating part is 10 to 700 nm.

A magneto-sensitive wire for a magnetic sensor with both measurement range expansion and environment resistance performance improvement, includes a Co-based alloy containing more Fe than a reference composition that is amorphous overall and exhibits zero magnetostriction. The Co-based alloy may have an Fe ratio (Fe/(Co+Fe+Ni)) of 6.1% to 9.5%. The Fe ratio is an atomic fraction of the Fe amount with respect to the total amount of a magnetic element group consisting of Co, Fe, and Ni. By heating an amorphous wire of a Co-based alloy at a temperate at least equal to a crystallization start temperature and lower than a crystallization end temperature, allows the magneto-sensitive wire to have a composite structure in which crystal grains are dispersed in the amorphous phase. The magneto-sensitive wire's anisotropy field is, for example, 5 to 70 Oe and the stress sensitivity, indicative of magnetostriction, is −30 to 30 mOe/MPa.

A Fe-based alloy represented by a composition of (Fe.sub.(1-a)M.sup.1.sub.a).sub.100-b-c-d-e-f-gM.sup.2.sub.bM.sup.3.sub.cB.sub.dP.sub.eCu.sub.fTi.sub.g, wherein M.sup.1 is at least one element selected from the group consisting of Co and Ni, M.sup.2 is at least one element selected from the group consisting of Nb, Mo, Zr, Ta, W, Hf, Ti, V, Cr, and Mn, M.sup.3 is at least one element selected from the group consisting of Si, Al, Ga, and Ge, and a, b, c, d, e, f, and g satisfy the following content conditions: 0≤a≤0.5, 0<b≤1.5, 0<c≤4, 7≤d≤13, 0.1≤e≤5, 0.6≤f≤1.5, and 0<g, is provided, wherein a full width at half maximum of an XRD main peak is 0.172 or more.

Provided is an Fe-based nanocrystalline alloy powder. The Fe-based nanocrystalline alloy powder has a chemical composition, excluding inevitable impurities, represented by a composition formula of Fe.sub.aSi.sub.bB.sub.cP.sub.dCu.sub.eM.sub.f, where the M in the composition formula is at least one element selected from the group consisting of Nb, Mo, Zr, Ta, W, Hf, Ti, V, Cr, Mn, C, Al, S, O, and N, 79 at %≤a≤84.5 at %, 0 at %≤b<6 at %, 0 at %<c≤10 at %, 4 at %<d≤11 at %, 0.2 at %≤e≤0.53 at %, 0 at %≤f≤4 at %, a+b+c+d+e+f=100 at %, a degree of crystallinity is more than 10% by volume, and an Fe crystallite diameter of the Fe-based nanocrystalline alloy powder is 50 nm or less.

An alloy particle contains: total content of Fe and Co: from 82.2 to 96.5 parts by mass; Co: 0 to 30.0 parts by mass; P: 0 to 4.5 parts by mass; B: more than 0 to 5.0 parts by mass; C: 0 to 3.0 parts by mass; Si: 0 to 6.7 parts by mass; Ni: more than 0 to 12.0 parts by mass; Cr: more than 0 to 4.2 parts by mass; total content of Mo, W, Zr, and Nb: 0 to 4.2 parts by mass; total content of P and Cr: 7.4 parts by mass or less; multiplication product of the parts by mass of Ni and Cr: 0.5 or more; and total content of Fe, Co, and Ni: 97.0 parts by mass or less. The alloy particle contains an amorphous phase, and a volume percentage of the amorphous phase is 70% or higher.

An alloy particle contains: total content of Fe and Co: from 82.2 to 96.5 parts by mass; Co: 0 to 30.0 parts by mass; P: 0 to 4.5 parts by mass; B: more than 0 to 5.0 parts by mass; C: 0 to 3.0 parts by mass; Si: 0 to 6.7 parts by mass; Ni: more than 0 to 12.0 parts by mass; Cr: more than 0 to 4.2 parts by mass; total content of Mo, W, Zr, and Nb: 0 to 4.2 parts by mass; total content of P and Cr: 7.4 parts by mass or less; multiplication product of the parts by mass of Ni and Cr: 0.5 or more; and total content of Fe, Co, and Ni: 97.0 parts by mass or less. The alloy particle contains an amorphous phase, and a volume percentage of the amorphous phase is 70% or higher.

A soft magnetic powder containing a particle having a composition represented by Fe.sub.xCu.sub.aNb.sub.b(Si.sub.1-yB.sub.y).sub.100-x-a-b, a, b, and x being numbers whose units are atomic %, in which 0.3≤a≤2.0, 2.0≤b≤4.0, 75.5≤x≤79.5, and y is a number satisfying f(x)≤y≤0.99, and f(x)=(4×10.sup.−34)x.sup.17.56. The particle includes a crystal grain having a grain size of 1.0 nm or more and 30.0 nm or less and containing a Fe—Si crystal, a Cu segregation portion having a grain size of 2.0 nm or more and 16.0 nm or less in which Cu is segregated, and a crystal grain boundary adjacent to the crystal grain and having a Nb concentration and a B concentration higher than a Nb concentration and a B concentration in the crystal grain. A number proportion of the Cu segregation portion is 80% or more.

A soft magnetic powder containing a particle having a composition represented by Fe.sub.xCu.sub.aNb.sub.b(Si.sub.1-yB.sub.y).sub.100-x-a-b, a, b, and x being numbers whose units are atomic %, in which 0.3≤a≤2.0, 2.0≤b≤4.0, 75.5≤x≤79.5, and y is a number satisfying f(x)≤y≤0.99, and f(x)=(4×10.sup.−34)x.sup.17.56. The particle includes a crystal grain having a grain size of 1.0 nm or more and 30.0 nm or less and containing a Fe—Si crystal, a Cu segregation portion having a grain size of 2.0 nm or more and 16.0 nm or less in which Cu is segregated, and a crystal grain boundary adjacent to the crystal grain and having a Nb concentration and a B concentration higher than a Nb concentration and a B concentration in the crystal grain. A number proportion of the Cu segregation portion is 80% or more.

A soft magnetic powder of the invention has a composition represented by Fe.sub.100-a-b-c-d-e-fCu.sub.aSi.sub.bB.sub.cM.sub.dM′.sub.eX.sub.f (at %) [wherein M is Nb, W, Ta, Zr, Hf, Ti, or Mo, M′ is V, Cr, Mn, Al, a platinum group element, Sc, Y, Au, Zn, Sn, or Re, X is C, P, Ge, Ga, Sb, In, Be, or As, and a, b, c, d, e, and f are numbers that satisfy the following formulae: 0.1≤a≤3, 0<b≤30, 0<c≤25, 5≤b+c≤30, 0.1≤d≤30, 0≤e≤10, and 0≤f≤10], wherein a crystalline structure having a particle diameter of 1 nm or more and 30 nm or less is contained in an amount of 40 vol % or more, and the difference in the coercive force of the powder after classification satisfies predetermined conditions.

A crystalline Fe-based alloy powder composed of Fe-based alloy particles containing, within a structure thereof, nanocrystal grains having an average grain size of 30 nm or less, and in which d50, which is a particle diameter corresponding to a cumulative frequency of 50% by volume, is from 3.5 μm to 35.0 μm in a cumulative distribution curve that is obtained by laser diffractometry and that shows the relationship between the particle diameter and the cumulative frequency from the small particle diameter side, and a ratio of Fe-based alloy particles having a particle diameter of 2 μm or less to the total of the Fe-based alloy particles, which is determined by laser diffractometry, is from 0% by volume to 8% by volume.