Permalloy, the iron-nickel alloy, has a wide range of nickel content, between 35% and 90%. The most important characteristic of PoMo alloys is their high permeability to weak magnetic fields. Their saturation magnetic induction strength is generally between 0.6 and 1.0 T.

Permalloy is often referred to as an iron-nickel alloy, with nickel content in the range of 30 to 90%. It is a very widely used soft magnetic alloy. With proper process, the magnetic properties can be effectively controlled, such as initial permeability over 105, maximum permeability over 106, coercive force as low as 2‰Oster, rectangular coefficient close to 1 or close to 0. Permalloy with face-centered cubic crystal structure has very good plasticity and can be processed into ultra-thin strips of 1μm and various use forms. Commonly used alloys are 1J50, 1J79, 1J85, etc.
The saturation magnetic induction strength of 1J50 is slightly lower than that of silicon steel, but the magnetic permeability is tens of times higher than that of silicon steel, and the iron loss is 2~3 times lower than that of silicon steel. 1J79 has good overall performance and is suitable for high frequency low voltage transformers, leakage protection switch cores, common mode inductor cores and current transformer cores. 1J85 has an initial permeability of over 100,000 (105) and is suitable for weak signal low frequency or high frequency input and output transformers, common mode inductors and high precision current transformers.

Permalloy is an iron-nickel alloy with high magnetic permeability in weaker magnetic fields. Nickel-iron alloys with nickel content above 30% are single-phase face-centered cubic (γ) structures at room temperature, but the single-phase structure near 30% Ni is very unstable, so practical iron-nickel soft magnetic alloys with nickel content above 36%. Near the nickel content of 75% (atomic fraction) of FeNi alloys, a Ni3Fe long-range ordered transition occurs in this single-phase alloy, when the dot constants and physical properties of the alloy, such as resistivity and magnetism, are changed. Therefore, the effect of the ordered transition on the properties has to be considered. Additional elements such as small amounts of Mo or Cu are usually added to Ni3Fe alloys to suppress the generation of long-range ordered.

The production process of Permalloy is complicated. For example, the rolling process, annealing temperature and time, and the cooling speed after annealing all have a great influence on the final magnetic properties of the material.China's Permalloy grade is 1JXX, where J means "precision alloy", "1" means soft magnetic, and the number after is the serial number, which usually indicates the amount of nickel in the alloy. For example, 1J50, 1J851, etc. Permalloy has high permeability, so it is often used in the core of medium and high frequency transformers or in devices with strict requirements for sensitivity, such as high frequency (tens of kHz) switching power transformers, precision transformers, leakage switching transformers, magnetic shields, magnetic yokes, etc.