Mumetal Toroidal Cores

Material Specification - Mumetal

AEM Cores currently stocks Vacoperm 100, manufactured and sourced from Germany.

We are continually researching alternative steel suppliers in an effort to reduce costs, improve quality and maintain consistent magnetic performance.


Inlac Coating

After slitting we coat the Mumetal strip on either side with a magnesium oxide solution to assist in the heat treatment of the steel. After drying the carrier fluid evaporates leaving a fine, consistent layer of inert magnesium oxide powder adhered to the surface of the strip. When wound into a toroid, this powder physically separates the laminations and reduces the possibility of inter lamination welding. It also helps prevent shot spots and wicking in the core, to ensure the material is consistently annealed.


Handling Considerations

Mumetal is extremely sensitive to adverse stress and hence should be handled with care.
A satisfactory core can be magnetically damaged simply by dropping it on the table, squeezing it with finger force, incorrect copper winding tension, incorrect mounting and assembly or even by vibration from transit or whilst in operation.


It cannot be expressed enough that delicate handling, correct winding procedures and careful consideration for induced stress must be paramount when dealing with Mumetal. Stress is additive from the time the parent roll leaves the annealing furnace at AEM Cores. Every effort is made to ensure the cores are at peak performance by the time they leave our store. We will not accept responsibility for end user handling errors leading to increased stress and reduced magnetic response. Often we cannot re-anneal a damaged Mumetal core; therefore we encourage our customers to handle these cores with care.


  • NEVER stand a Mumetal core on it's edge.
  • ALWAYS use two hands to pick them up.
  • NEVER flex or deform a core, the material is extremely strain sensitive.


To counter the effects of stress on Mumetal Toroidal cores in the transportation and winding processes each core is individually treated with an air drying insulation varnish.

The colour and outer texture of a Mumetal core will vary depending on the quality of the atmosphere and impurity level within the furnace. It has NO effect on the magnetic properties nor is it an indication of the core performance.