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Magnetization
The effect of magnetization is fundamental and arises when an object is exposed to a magnetic field. The magnetization magnetizes material that was previously not magnetic. Strong magnetization can only be realized with ferromagnetic substances, for example nickel, iron or cobalt. In the material itself, the parallel alignment of all elementary magnets ensures magnetization. They align themselves with the outer magnetic field. Hard blows, oppositely polarized fields or high temperatures can destroy the magnetization. One speaks then of a demagnetization. The magnetization itself creates a magnetic field within matter. This is superimposed with the external magnetic field. In principle, substances are distinguished in three different properties: diamagnetic, ferromagnetic and paramagnetic.
Paramagnetism, diamagnetism and ferromagnetism
Then we are talking about paramagnetism when the magnetization is rectified to the external magnetic field. The same is the case with ferromagnetic bodies: The magnetization is also rectified here outside the magnetic field. In contrast to the paramagnet, however, this orientation is much more stable. The reason for this is a special interaction called exchange interaction. For diamagnetic material the magnetization is directed against the external magnetic field. Especially with ferromagnetic materials such as cobalt or iron, a strong magnetization is observed.
Experiment - recreate magnetization at home
This experiment requires a magnet and a ferrous object- such as a pair of scissors or a pin, or a fork. When the magnet attracts the corresponding object, it is an article with ferromagnetic components or properties. The actual start of the experiment begins by exposing the ferrous object to the magnetic field of the magnet. The magnetic field should be constant and not change. After the magnet has been removed, it can be shown that the iron-containing object, such as the scissors or spoons, are now themselves magnetic. For example, magnetized pins will stick to the scissors. This remaining magnetization is called remanence.
Magnetic permeability
About the so-called magnetic permeability μ, the magnetization M, which in turn sets within an external magnetic field determined.
To understand this formula, it is important to know the different effects. Simplified, the permeability μ indicates how strongly the magnetic field H changes when an external magnetic field and the influence of matter are applied. The following applies:
The above-apparent formula (1) is given for the reason that the magnetic field H is the sum of the magnetization of the body and the external magnetic field. Example: Since the permeability μ of the vacuum is equal to 1, the magnetization M = 0. The above-mentioned different properties can be fixed on the permeability μ: For paramagnetic substances, the permeability μ is slightly greater than 1, the magnetization is therefore positive or rectified. For diamagnetic substances, the permeability μ is less than 1, so the magnetization negative and thus opposite to the externally applied field. For superconductors, the permeability μ is 0. Now we also know why superconductors float: There is no field inside the superconductor, since the magnetization of the superconductor is directed counter to the external field and of equal magnitude. Large permeability figures are found for ferromagnets: The permeability μ can go up to 10,000 for iron, for special metals, so-called amorphous, even up to 150,000. The magnetization for large μ and an external magnetic field H is approximately equal to the product of μ and the external magnetic field:
Magnetization explained in more detail
The electrons are the main reason for the magnetization effect. To understand the following sentences, it helps to imagine in your mind the atomic arrangement of a material - that is, the atoms with their atomic nuclei and electrons.
As we know, electrons move in a changing magnetic field or drift when moving in a constant field (keyword Lorentz force). When an external magnetic field is applied, the movements of the electrons in the atomic sheaths are of interest. This causes the so-called diamagnetism. There exists a so-called Lenz's rule, which states that these currents counteract the cause by their direction. Now also explains why the magnetization in the material is directed against the outer field.
However, the diamagnetism of the substance can be superimposed by stronger properties such as paramagnetism or ferromagnetism. The reason is the electron spin of each electron. This spin has magnetic properties: these are the elementary magnets in the material. A spin has a fixed magnetic moment. Overlapping usually occurs when the number of electrons is odd. For then two opposing spins in the totality can not overlap: A spin remains, which can align itself with the external magnetic field. The magnetization is accordingly directed against the external field.
Ferromagnets stabilize this alignment of the electron spins through the above-mentioned exchange interaction. Thus, a ferromagnetic material remains significantly magnetic even after removal of the external magnetic field. Remanence can not only be measured but also subjectively observed very well. Paramagnetic material - for example molten aluminum - or paramagnets are no longer magnetic at the moment when the external magnetic field is removed. Accordingly, no remanence can be observed here. The above-mentioned demagnetization by heat, an opposite magnetic field or by strong shocks can be attributed to the fact that these effects mix the electron spins or the aligned elemental magnets again. Especially when heated, magnetization occurs at a certain temperature. This temperature threshold is called the Curie temperature.