Permalloy structure explanation

Permalloyis an iron-nickel alloy with a wide range of nickel contents, ranging from 35% to 90%. The most notable feature of Permalloy is its extremely high weak magnetic field permeability. Its saturation magnetic induction intensity is usually in the range of 0.6 to 1.0 Tesla (T).

Hysteresis loop of magnetic materials:
When the external magnetic field of a magnetic material changes, the relationship between the magnetic induction intensity B and the external magnetic field intensity H will form a closed curve that is approximately rectangular. This curve is called a hysteresis loop. The hysteresis loop is an important feature of magnetic materials. The hysteresis loop of hard magnetic materials is relatively "large", while the hysteresis loop of Soft Magnetic materials is relatively "small".

Structure and magnetic properties of Permalloy:
Permalloy is an iron-nickel alloy that exhibits high magnetic permeability in a weak magnetic field. When the nickel content exceeds 30%, the nickel-iron alloy usually presents a single-phase face-centered cubic (FCC) structure at room temperature. However, when the nickel content is close to 30%, this single-phase structure is not stable. Therefore, the nickel content of the iron-nickel soft magnetic alloy in practical applications is usually above 36%.
When the nickel content of the iron-nickel alloy approaches 75% (atomic fraction), a long-range order transition of Ni3Fe will occur in this single-phase alloy. At this time, the lattice constant of the alloy and the physical properties (such as resistivity and magnetism) will change. Therefore, when designing the alloy, the effect of this order transition on the performance must be considered. In order to suppress the generation of long-range order, a small amount of additional elements such as Mo or Cu are usually added to the Ni3Fe alloy.