Ferromagnetism occurs in materials that contain unpaired spins between which an interaction that results in the Atomic magnetic moments align themselves parallel to each other. This leads to spontaneous and permanent magnetic fields around an object that is made from a ferromagnetic material.
Though in a material usually both interactions are that want to put in the same direction as the spins interactions that dominate the spins correctly put in the opposite direction, so the first forces in a Ferromagnet. (Otherwise there antiferromagnetism.)
In principle, all spins in the same direction in a Ferromagnet come to be – in this case reached the subject magnetic saturation and possesses a large spontaneous magnetic field. However, it is also possible that the organisation of the spins into smaller domains, the so-called areas of Weiss takes place. If the magnetization direction of the domains is arbitrary, the total field of the object is zero, although there is talk of magnetic planning. By exposure to a strong external field can all be drawn in the same direction (magnetized) domains.
In increasing the temperature the temperature gradually breaking the movement for a spin order. At a certain temperature, the Curie temperature, the organisation joined forces because the increased heat energy than the energy of the magnetic interaction. TC above the material behaves, the reciprocal ParaMagneticsusceptibility plotted against the absolute temperature then forms the characteristic straight line of a para magnet. However, the line goes by T = T(C) instead of by T = 0 K due to the interaction between the spins will exist even though prevents the thermal energy the system.
The magnetic permeability and thus the magnetic susceptibility in ferromagnets is not constant, but a non linear function of field strength H and landscaped by the magnetiseringsvoorgeschiedenis. Therefore, it is usually the (differential) magnetic susceptibility to magnetization as derivative of the field strength considered. The magnetization is zero in the saturation area.
If the material is magnetically saturated, retain the magnetization remains a constant value , which applies:
At the building of a periodically changing external magnetic field goes through the magnetization of a ferromagnetic material a magnetiseringscurve. Outgoing from "Virgin" material with no net magnetization is at first time installation of an external field H through the blue curve. Upon reaching the saturation flux density magnetic field strength at the magnetization not advance far. If then the field is reversed, with the magnetization field strength H = 0 is not yet entirely reduced to zero, there is a remanente field strength due to the yet again to its original state come from the areas of Weiss. Only when the external field strength imposed a oppositely directed value, has reached the coercivity is B = 0. Through the surface of the loop at wisselmagnetisering is a measure of the losses. Materials with low values of hystereselussen are so small and soft magnetic materials listed. On the other hand, Is very large, then one speaks of hard magnetic material.
The most famous ferromagnets are iron and nickel, but there are a number of newer materials because of their particularly strong ferromagnetic behavior begin to find much application. They are based on lanthanide elements, for exampleCo5 SmandNdFeB. For practical application in the electrical engineering steel is processed into laminated transformer look. Stainless steelis not necessarily magnetic although it contains a high proportion of iron. Of the 300 series stainless steels from the AISI are austenitic non-magnetic and therefore in delivered status. Stainless steels of the 400 series from the AISI as well as duplex stainless steels are magnetic.
Ferromagnetic materials common two main areas of application: hardmagnetische permanent magnets, which materials are used, and cores for coils, solenoids and transformers and electric motors look packages fordynamo's. for the last applications zachtmagnetische materials, for example transformer look and dynamo look used. The ferromagnetic core or the can package increases the inductance of the coils, causing the magnetiseringsstromen remain small, and joins the magnetic field generated by the coil.