Magnetic materials

Magnetic materials (also called magnetic materials ) are substances that are used technically because of their magnetic properties. The distinction that has grown over time is the division into soft magnetic and hard magnetic materials. There are also metals and metal alloys that have ferromagnetic properties, such as steels , but which are used, for example, as construction materials due to their mechanical properties. At the beginning of the 20th century , the soft magnetic materials were also mechanically soft, the materials that made good permanent magnets were more mechanically hard. This rule no longer applies, at least since the development of amorphous metals.

Rough division

Overview diagram of magnetic materials

Soft magnetic materials are characterized by their easy magnetizability, which is expressed in a small coercive field strength . In simple terms, small external magnetic fields can change the internal alignment of the elementary particles.

Hard magnetic materials ( permanent magnets ) have very high coercive field strengths and accordingly offer high resistance to external magnetic fields. Magnetization reversal (or demagnetization) can only be achieved with very strong external fields.

The coercive field strength Hc used as a common classification criterion for magnetic materials is the field strength at which the induction (polarization) left behind by magnetization disappears again. In a hysteresis loop represents the passage through the X-axis (the field strength H ). The coercive field strength is less dependent on the material itself as more faults in the material and the deviation from the ideal structure. The range at goes from 0.5 A / m for extremely soft magnetic materials to approx. 2000 kA / m for the best permanent magnets. The limit between the two material groups is around 1 kA / m. ${\displaystyle H_{c}}$ ${\displaystyle H_{c}}$

With soft magnetic materials, optimal properties are achieved if the elementary magnetization processes, wall displacements and turning processes take place as easily and uninhibitedly as possible.

For permanent magnet materials, precisely the opposite is sought in various ways. Wall displacements are hindered by inhomogeneities, attempts are made to hinder turning processes by crystal and shape anisotropies .

Further distinguishing features for magnetic materials are the saturation polarization ( ), the remanence ( ), the permeability , the losses ( p ) and the loop shape of the hysteresis loop . In principle, all of these properties can be derived directly or indirectly from the hysteresis loop. ${\displaystyle J_{s}}$ ${\displaystyle B_{r}}$ ${\displaystyle \mu _{r}}$

Soft magnetic materials are:

• Alloys based on iron, nickel and cobalt and other additives, crystalline
• Alloys based on iron, nickel and cobalt and other additives, amorphous and nanocrystalline
• Powder materials
• Soft ferrites (NiZn, MnZn)

Hard magnetic materials are:

• Cobalt samarium (SmCo ₅ , Sm ₂ Co ₁₇ , Sm (Co, Cu, Fe, Zr) _z )
• Neodymium-Iron-Boron (NdFeB)
• AlNiCo alloys
• Hard ferrites based on barium , strontium
• PtCo alloys
• CuNiFe and CuNiCo alloys
• FeCoCr alloys
• martensitic steels
• MnAlC alloys

literature

• Siegfried Buchhaupt: Development and Significance of Magnetic Materials . In: Technikgeschichte, Vol. 68 (2001), H. 4, pp. 335-353.