Basics
Understanding ferromagnetic materials
In ferromagnetic materials such as iron and steel, microscopic regions with uniform magnetic alignment form. These so-called Weiss domains typically have a volume of 0.001 to 0.1 mm³ and are separated from each other by the so-called Bloch walls. The magnetization state of the material is determined by the alignment of these domains.
Understanding the fundamentals
Magnetization process
When an external magnetic field of increasing strength is applied:
- The molecular magnets in the individual Weiss domains begin to align.
- With increasing field strength, the Bloch walls irreversibly shift in small jumps (Barkhausen jumps)
- As the magnetic field continues to increase, larger uniformly aligned areas form (Bloch wall displacement completed).
- If all molecular magnets are aligned parallel to the external magnetic field, the material is said to be magnetically saturated.
After removing the external magnetic field, a residual magnetism (remanence) remains.
Understanding the fundamentals
Demagnetization process
The purpose of demagnetization is to completely reverse the alignment of the Weiss domains and to create an externally non-magnetic state. The domains are then oriented so that the magnetic flux is largely contained within the material itself:
- A strong alternating field first aligns all the molecular magnets in the direction of the external field.
- The step-by-step, but half-wave-symmetrical reduction of the field strength allows a reorientation and thus a “freezing” of disordered domains.
- The “shaking effect” or the rotation processes of the frequency generate a fine but disordered domain structure.
- Demagnetization occurs from the inside out. It is important that the initial field strength is high enough and the frequency is low enough to reach the domains in the core of the material.