Mu Metal is one of a family of three nickel iron alloys widely used to produce magnetic parts and shielding. The three alloys concerned have the following approximate compositions and well known trade names:
36%NiFe widely known as Supra 36, Nilomag36, Radiometal 36, Magnifer 36
50%NiFe widely known as Supra 50, Nilomag 50, Radiometal 50, Magnifer 50
80%NiFe 5%Mo widely known as Mu Metal, Magnifer
For shielding applications it is possible to use a combination of two or more layers of these alloys to arrive at the correct level of shielding without the shield becoming saturated.
For example: a combination of Mu Metal and a 50%NiFe is frequently used.
The 50% material has a much higher saturation level and can reduce the effect of any magnetic field substantially, leaving a second layer of Mu Metal to further reduce the effect on the shielded item because of its much higher permeability without becoming saturated. This is due to the fact that the 50% material has already reduced the magnetic field level considerably before it reaches the Mu Metal layer.
Relative properties of these three materials are shown below:
Max Permeability Saturation Flux Density (Tesla)
Mu Metal 400000 0.76
50% NiFe 100000 1.60
36%NiFe* 25000 1.30
*36% material is used mainly for low cost shieldings.