Soft magnetic materials
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:
- Metals (solid, bonded powder, sheet metal, crystalline or amorphous ribbons, previously also wires)
- ceramic materials ( ferrites )
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:
- Iron (so-called " soft iron ")
- Low carbon steels
- Steels with added silicon ( FeSi ), electrical sheet and strip
- Other types of steel
- Nickel- iron alloys (FeNi)
- Cobalt- iron alloys (FeCo)
- Other alloys (e.g. FeAl, FeAlSi)
- Ferrites
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:
- Motors and generators
- Transformers , transformers, chokes , coils , baluns
- Relays and contactors
- Residual current circuit breaker (FI circuit breaker)
- Components for ultrasonic generation ( magnetostriction )
- Mechanical filters and delay lines
- Magnetic head for storing information in hard magnetic materials ( magnetic tape , hard drive , magnetic stripe , and previously also wires)
- Anti-theft device ( security label )
- Inductive sensors
- Reed contacts
- Ferrite antennas
literature
- Gerhard M. Fasching: Materials for electrical engineering: microphysics, structure, properties . 4th edition. Springer, 2005, ISBN 978-3-211-22133-4 .