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Small Introduction to Permanent Magnetism

We provide a very short tutorial to the field of permanent magnetism.  This includes the basics of  magnetic fields, the different classes of magnets as well as magnetic materials and their characteristic parameters. It also includes insights into stability issues, magnetic simulation as well as atomic origins of magnetic effects.

The different lessons can be dowloades as pdf-files, click on the icons. 

Basic Parameters of Permanent Magnetism

This article offers an explanation of the most important parameters of permanent magnetism like magnetization, magnetic moment, magnetic polarization, susceptibility, permeability and others. Here we also depict the famous Maxwell equations as well as the difference between the so called H- and B- fields. Additionally the reader will be introduced into basic magnetic phenomena like ferromagnetism, paramagnetism, diamagnetism and how magnetic hysteresis or the basic polarization curves look like for permanent and soft ferromagnetic materials.

Hysteresis and Demagnetization Curve

Here we will have a closer look on magnetic hysteresis. Whereas the first quadrant of hysteresis describes the magnetizing behavior of respective materials at external fields, the second quadrant is very important for the operation of already magnetized magnets. The second quadrant is often called demagnetization curve. The most important parameters for the demagnetization curve like remanence induction, coercivity or maximum energy product are explained here. Additional terms like demagnetization factor, internal field and others will be treated also. 

Stability of Permanent Magnets

The stability of permanent magnets, i.e. the question when fields or forces of  magnets are constant, is important from technical and from general viewpoints. Changes of magnetic characteristics are basically classified into reversible and irreversible effects. Both sorts can be originated by changes of temperature or by external magnetic fields. Whether reversible or irreversible processes take place is governed by the so called load line, which describes the status of internal and external fields in the material. The explanation of the most relevant aspects, basic contexts and mechanisms will be shown here.

Magnetic Materials

Here the most important commercially available permanent magnetic materials will be described. In detail these are ceramic Ferrites, NdFeB, Samarium Cobalt and Alnico alloys. They still govern the world wide market for permanent magnets. Beside a general explanation of their specific characteristics we will also show a table, which provides the range of values for basic parameters like remanent polarization, coercivity or the temperature coefficient of Br.  Also cost and stability aspects and the major technical applications are depicted briefly.

Computation of Permanent Magnetic Fields

This chapter will deal with the computation of magnetic fields that are originated by permanent magnets. Beside a general explanation of the basic differential equations, a short introduction to numerical methods like the FEM method will be given. The analytical treatment of permanent magnets will then be explained in detail by showing the related formulas. Such analyses can be done by use of the magnetic vector potential as well as by using the magnetic scalar potential. A short introduction to some of the basic subjects of mathematical vector analysis completes this chapter.

Atomic Origins of Magnetism

Here follows an explanation of the quantum theoretical origins of the electrons magnetic moment, which results from spin and angular momentum. In addition we elucidate the coupling of the moments of the single electrons to form the total magnetic moment of the atom. The mutual interactions of the atoms will be discussed then, which lead to the phenomena of ferromagnetism, paramagnetism and diamagnetism under the action of fields and temperature. Related equations for the magnetic moment, especially for ferromagnetic matter, are briefly sketched in addition.

Mechanisms of Hysteresis

Here we will try to explain the basis phenomena hwich contribute to the effect of magnetic hysteresis. Those are subjects like domain nucleation, domain pinning or domain wall movement. We will additional mention the so called single domain particel model, where a particle only consists of one magnetic domain and changes follow from rotation and switching of magnetization. In a very short manner there sould alo be mentioned the theory of micromagnetism, by which basic calculations and simulations of related effects can be performed.

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