The magnetization when a strong field aligns all the magnetic moments in the same direction. For iron it is about 1.7×10⁶ A/m (about 2.2 T as µ₀Ms), and it decreases as the temperature rises.
Japanese name: 飽和磁化
Saturation magnetization appears in 8 practice questions across 2 topics, including Magnetic materials, Electronic, magnetic and optical materials.
Field: Magnetic materials
Saturation magnetization Ms is the magnetic moment per unit volume when a strong field aligns all the moments in one direction, in units of A/m. Because it is set by the moment per atom and the number density of atoms, for a given composition and temperature it hardly depends on grain size or the degree of working. In this it differs in character from coercivity and permeability, which change greatly with microstructure, and it is treated as a structure-insensitive quantity. In designing magnetic materials, the magnitude of the saturation magnetization is first fixed by composition, and coercivity and permeability are then adjusted by controlling the microstructure.
Compared as the room-temperature saturation flux density µ₀Ms, iron gives about 2.15 T, cobalt about 1.8 T and nickel about 0.6 T, with moments per atom at 0 K of about 2.22, 1.72 and 0.61 µB respectively. An alloy of iron with about 35% cobalt reaches about 2.4 T, the highest value among practical materials. Iron-based amorphous alloys, by contrast, are lower at about 1.5 to 1.6 T, and Mn-Zn ferrites at about 0.5 T. The value is sometimes given per unit mass instead of per unit volume; expressed this way, the saturation magnetization of iron is about 218 A·m²/kg (218 emu/g).
As temperature rises, thermal fluctuations make it harder for the moments to stay aligned, and the saturation magnetization decreases. On heating from 0 K it falls slowly at first, then rapidly near the Curie temperature, where it reaches 0. The Curie temperature is about 770°C for iron, about 358°C for nickel and about 1120°C for cobalt. Room-temperature values are somewhat smaller than those at 0 K; for nickel, for example, the 0 K value calculated from the atomic moment is about 0.64 T, compared with about 0.61 T at room temperature. For motor and transformer materials used at high temperature, the saturation magnetization at the service temperature must be considered.
Because flux density is B = µ₀(H + M), the flux density at saturation Bs is µ₀Ms plus µ₀H, but in soft magnetic materials µ₀H is small, so Bs ≈ µ₀Ms is used. Remanence is the magnetization left when the field is returned to 0; it is smaller than the saturation magnetization and depends strongly on microstructure and shape. In measurement, the magnetization curve is taken with a vibrating sample magnetometer (VSM) or a SQUID magnetometer and the saturated value is read at high field. A demagnetizing field due to the specimen's shape means a strong field is needed for saturation, so measures are taken such as placing a long, thin specimen along the field.
Answer: B. About 1.7×10⁶ A/m
A BCC unit cell contains 2 atoms, so the number density of atoms is n = 2/a³ = 2/(0.2866×10⁻⁹ m)³ ≈ 8.50×10²⁸ m⁻³. The saturation magnetization is the magnetic moment per unit volume, so Ms = n × 2.22 µB = 8.50×10²⁸ × 2.22 × 9.27×10⁻²⁴ ≈ 1.7×10⁶ A/m. Expressed as µ₀Ms this is about 2.2 T, in good agreement with the saturation flux density of iron. About 8.7×10⁵ A/m counts the unit cell as containing 1 atom, and about 3.5×10⁶ A/m counts 4 atoms as in FCC. The moment per atom is not a whole number because the 3d electrons responsible for magnetism form a band.
Saturation magnetization Ms is the density of magnetic moment in the material, in A/m, and saturation flux density Bs is the flux density at saturation, in T. From B = µ₀(H + M), Bs is larger than µ₀Ms by µ₀H, but the difference is small, so the two are sometimes used almost interchangeably.
In SI units it is A/m and in CGS units emu/cm³, with 1 emu/cm³ = 1000 A/m. Expressed as flux density, µ₀Ms (T) is used, or 4πMs (G) in CGS, with 1 T = 10000 G. Values per unit mass have the same number in A·m²/kg and emu/g.
Hardly at all, as long as the composition and phases do not change. If heat treatment forms precipitates or a phase transformation or ordering produces a different phase, however, the overall saturation magnetization changes because each phase has a different value. Austenitic stainless steel becoming martensite on working and starting to stick to magnets is an example.
The saturation magnetization is the magnetic moment per unit volume, so Ms = n × 2.22 µB = 8.50×10²⁸ × 2.22 × 9.27×10⁻²⁴ ≈ 1.7×10⁶ A/m.
Take the magnetic moment per atom of iron (BCC, lattice par…As the field is increased further, the magnetization within the remaining domains itself rotates toward the field direction, approaching the saturation magnetization.
When an external magnetic field is applied to a demagnetize…Macroscopically a ferrimagnet shows domains and hysteresis just as a ferromagnet does, but its saturation magnetization is smaller than that of ferromagnetic metals such as iron.
Which statement correctly describes the ferrimagnetism show…The value obtained from the measured saturation magnetization is about 4.1 µB, in good agreement with this estimate.
Magnetite Fe₃O₄ has the inverse spinel structure: the A sit…The saturation flux density of permalloy is considerably lower than that of pure iron (about 2.2 T), so the option citing a saturation magnetization larger than that of pure iron is wrong.
What is the main reason permalloy, Fe with about 78% Ni, sh…Magnetic domain Coercivity Magnetocrystalline anisotropy Maximum energy product Domain wall Ferrimagnetism Spinel structure Curie temperature Eddy-current loss Superparamagnetism