What material is best for shielding a magnet?

Shielding a magnet or attempting to block a magnetic field is a subject that several of our customers approach our experts with on a regular basis, so we decided to examine what materials can be used to shield a magnet.

Before learning how to shield a magnet it’s important to know that magnetic shielding does not block a magnetic field. No material can stop the lines of flux from travelling from a magnet’s north to its south pole. However, it can be redirected.

The simplest example of this would be putting a steel keeper across the poles of a horseshoe magnet, as the magnetic flow is still present but will flow through the steel so there is no external magnetic field.

The most common reason in which we will shield or attempt to block a magnetic field is when we send highly magnetised materials overseas. Airlines state that there should be no magnetism outside the box.

Which material will work?

Any ferromagnetic metal. That is any metal containing iron, nickel or cobalt. Many steels are ferromagnetic metals and will work for redirecting magnetic shields.

Steel is the commonly used metal because it is cost-effective and widely available, however some stainless steels are not ferromagnetic.

How thick should my shield be?

The magnetic field will be affected by the thickness of the metal being used to shield it, however figuring out how thick the shield needs to be is dependant on several factors.

For example, you must consider the size of the magnetic field you are shielding, what is being shielded from, what is the shields shape and finally does it make sense to shield the magnet.

The thickness of your shield is important as if the shield is too thin it can become saturated and will not be able to hold any more lines of flux, so therefore you need the shield to be thick enough to hold as much flux as possible. However, after a certain point adding steel thickness will not improve shielding.

In some cases where saturation become an issue, multiple layers of materials can be used.

Are there other materials that can be used?

There are some specialised materials designed and made for magnetic shielding. The most common of these specialised materials is MuMetal, or some other proprietary alloys.

Most of these will have a high nickel content, with either 50% or 80% nickel content.

These specialised magnetic shielding materials will have a higher relative permeability but a lower saturation point. Permeability is the degree of magnetisation of a material responding linearly to an applied magnetic field.

When it comes to shielding the relative permeability is a measure of a material’s ability to absorb magnetic flux. The higher the number, the better the shield.

For example, low carbon steels have a permeability of 1000-3000, whereas specially designed metals can be as high as 300,000-400,00.

Making a final decision

So how to decide which material is right for your specific shielding problem.

If the magnet being shielded has low field strength, then specially made materials such as MuMetal can provide better shielding than steel. However, for applications that involve large, powerful neodymium magnets then the higher saturation points of steel prove useful and serves better.

Overall, many applications we come across and are asked about, a steel sheet-metal shield is usually the best solution.

If you still have any queries then be sure to get in touch with our team of experts who are available on 0845 519 4701 or sales@magnetexpert.com and are happy to help solve any problems or answer any questions you may have.

A magnet in a free space.
A magnet next to a steel wall.
A magnet in a steel enclosure.

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