Soft magnetic materials

from Wikipedia, the free encyclopedia
Hysteresis curve of a magnetically soft transformer core

Soft magnetic materials are materials that can be easily magnetized in a magnetic field . This magnetic polarization can e.g. B. generated by an electric current in a current-carrying coil around a magnetic core or by the presence of a permanent magnet . In all soft magnetic materials, the polarization leads to a much higher magnetic flux density than the external magnetic field in air. Put simply, a soft magnetic material "strengthens" an external magnetic field around the material permeability . Soft magnetic materials have a coercive field strength of less than 1000 A / m. If an external magnetic field exceeds the coercive field strength, the direction of the magnetic flux in the material is also reversed.

Demarcation

In contrast to hard magnetic materials , such as permanent magnets , the hysteresis loss in soft magnetic materials when magnetizing is reversed, e.g. B. in a transformer or in the alternating field in generators and electric motors, kept small. Since the eddy current loss is to be reduced in addition to the hysteresis loss, resistance-increasing alloy additives such as silicon and aluminum (for iron alloys) are used for network-typical frequencies. Little or non-conductive ferrites are used at high frequencies .

Substance groups

Two soft magnetic groups of substances are used. The permeability and the losses are particularly important for differentiation:

The metallic materials are mainly based on the ferromagnetic metals iron , cobalt and nickel . There are three main groups: crystalline alloys, amorphous alloys, and nanocrystalline alloys.

The ceramic materials are primarily ferrites based on metal oxides , with the two substance families manganese-zinc (MnZn) and nickel-zinc (NiZn) in the foreground.

Classification

A classification is made in the IEC 60404-1 standard:

Designs

Widespread designs of soft magnetic materials or the external forms in which they are used are as follows:

  • Core sheets
  • Toroidal cores
  • Cut tape cores
  • Glued sheet metal packages
  • Molded and solid parts
  • Powder cores
  • Split core shapes such as UU, UI, EE, EI, EC, RM, shells (focus on ferrites)
  • Thin layers
  • Wires

Applications

The main applications for soft magnetic materials are predominantly in the field of electrical engineering and are:

literature

  • Gerhard M. Fasching: Materials for electrical engineering: microphysics, structure, properties . 4th edition. Springer, 2005, ISBN 978-3-211-22133-4 .