Permalloy in magnetic devices

What is Permalloy?

Permalloy, an iron-nickel alloy, contains a nickel content ranging from 30% to 90%, but most commonly, it has an 80% nickel and 20% iron composition due to its excellent magnetic properties. Originally, in 1914, Gustav Elmen of Bell Laboratories developed Permalloy for the purpose of telegraph cables, which they used for inductive compensation. Nevertheless, with time, it has become a cornerstone material in electronics and energy applications.

Performance Characteristics

Permalloy's magnetic properties make it stand out among soft magnetic materials:

Low Coercivity: By having a coercivity as low as 0.2 Oersted, the material is easily magnetized and demagnetized, ideal for dynamic magnetic field applications.

Near-Zero Magnetostriction: There is little change in dimension during magnetization, which makes it the most suitable for thin-film applications and tends to avoid the influence of stress-induced performance fluctuations.

High Permeability and Low Loss: It generally has a relative permittivity of about 100,000, moving up to 1,000,000, and low hysteresis loss, allowing power to be transferred with minimal inefficiency.

Anisotropic Magnetoresistance: The resistivity changes according to the direction of the magnetic field, making it suitable for magnetic sensors and storage devices.

Types of Permalloy

Permalloy is categorized into various types based on nickel content and added elements, with common grades including 1J50, 1J79, and 1J85.

1J50: It has a lesser saturation magnetic induction than silicon steel, although it is tens of times more permeable, and the iron losses are a couple of times lower. This core is quite useful in small transformers with a power range below the 400W limit and a frequency of 8000-100 Hz.

1J79: It has very good overall performance, so it is the ideal material for high-frequency and low-voltage transformers, magnetic cores of protection switches for ground fault detection, and inductor cores for common-mode filtering.

1J85: The good part about this alloy is it is feasible to achieve initial relative permeability greater than 100,000, so it can be used for the input or output idea of transformers in lower or higher frequency circuits, common-mode inductors as well as high-precision current transformers.

Combination with Neodymium Magnets

Permalloy and neodymium magnets are two fundamentally different types of magnetic materials. As is widely known, neodymium magnets have a strong permanent magnetism force and are the primary power source in most motors. At the same time, Permalloy is a high-permeability, low-loss material used for magnetic cores or shielding. The two are found in hybrid applications, such as:

Motors: Neodymium magnets generate a very strong magnetic field, while Permalloy serves as a magnetic core, which is becoming a factor in magnetic field optimization.

Transformers: Permalloy can efficiently focus the magnetic field in low-frequency surroundings, which in turn adds value to the transformer's performance.

It is essential to mention that the two materials mentioned above are not mixed directly, but they have a synergistic effect that helps the whole system work more efficiently.

Magnetic Field Shielding Principle

This high permeability of Permalloy enables it to effectively shield the magnetic field. Once met by a magnetic field, Permalloy causes the magnetic field lines to take a path along the material’s surface instead of going through, which in turn protects the shielded region from the surrounding magnetic field. Permalloy's characteristics are why it is mostly used as a protective material against magnetic fields.