Structure of a magnet – permanent magnet / electromagnet
In the previous chapter, we looked at how magnetism is formed. We have seen that there are different forms of magnetism (diamagnetism, paramagnetism, ferromagnetism), whereby only ferromagnetism (due to its strength) is visible or plays a role in everyday life.
In this chapter, we want to take a closer look at a "magnet". Due to the everyday and technical importance, the focus in the following will be on the permanent magnet and the electromagnet.
Permanent magnet and electromagnet
A permanent magnet (also known as a permanent magnet) is made of ferromagnetic materials such as iron, cobalt, nickel. However, a material made of a ferromagnetic material is not yet a (permanent) magnet. The material then has to be magnetized by a process. The main difference between a non-magnetized ferromagnetic material and a magnetized material is the internal atomic structure of the material.
As mentioned in the previous chapter, every substance has magnetic properties and is diamagnetic, paramagnetic, or ferromagnetic. Ferromagnetic substances (iron, nickel, cobalt and alloys made of these metals) have a special feature of their structure. In contrast to molecules, metals have free electrons in the metal lattice that can interact with an external magnetic field, as do compounds with an odd number of electrons. In contrast to paramagnetic materials, the magnetization in ferromagnetic materials is aligned with the external magnetic field and is particularly strong due to the interaction of electron spins.
In the atomic structure, there are magnetic regions with the same magnetic orientation due to the effect of the electron spin. These areas are usually arranged or aligned without order (for example in the case of an iron rod). In textbooks, these magnetic regions are referred to as Weissian districts or elementary magnets. Due to their disorder, the weak magnetic fields of the Weiss districts cancel each other out, so that there is little and no magnetic effect on the environment. This also explains why a (non-magnetized) iron bar does not become like a magnet.
The process of magnetization takes place because the so-called elementary magnets of a ferromagnetic material are aligned near a strong magnet. If a ferromagnetic substance is brought into an external magnetic field, then the Weissian regions align themselves along the magnetic field lines of the external field. The weak magnetic fields of the now "ordered" Weissian districts are now directed and act in one direction, i.e. they do not cancel each other out, but reinforce each other. The stronger the field created from the outside, the greater the alignment effect. Through this magnetization, the structure of ferromagnetic materials can be changed in such a way that they themselves exert a "magnetic" force on their environment for a long time.
Each magnet has two poles, with the north and south poles forming the two different poles of a permanent magnet, with the magnetic field running from the north pole to the south pole. The same applies to "magnetic poles" as to electrical charges. Poles of the same name repel each other (north and north poles, respectively south and south poles), while opposite poles attract each other. The magnetic force on a ferromagnetic material (e.g. iron) is attractive at the North Pole as well as at the South Pole, i.e. it is attracted by both poles.
Important: In contrast to charges (these can be separated "charge separation"), you cannot divide a magnet, so you only get a north pole or a south pole. Due to the atomic structure that magnetism allows, electromagnets cannot be divided, but the (orientation) of the electromagnets is also responsible for the fact that permanent magnets do not last for some time. Magnets lose their magnetic power over time (the order of the Weisss districts is lost). "Artificial" demagnetization can also be achieved by heating (heating above the Curie temperature) or by mechanical processing.
In summary: A permanent magnet (or permanent magnet) consists of a magnetized ferromagnetic material (iron, nickel, cobalt and alloys of these metals) that have been magnetized in a process and have retained their magnetic property ever since.
Electromagnet
Another type of magnet that is used in everyday life and technology is the so-called electromagnet. An electromagnet is a construction in which a strong magnetic field is caused by an electric current. Electromagnets consist of one or more coils.
If the electromagnet is connected to a power supply in a closed circuit and an electric current flows through the coil, a magnetic field is created around the conductor of the coil. The special thing about a coil is that the cable (often a wire) is wound on top of each other in many turns (like loops). As a result, each individual winding acts like a circular conductor, with the individual magnetic fields superimposed to form an entire field.
The magnetic effect of a current-carrying coil can be increased even more. If an iron core is placed in the coil, the magnetic field is additionally strengthened (alignment of the Weissian regions in the iron strengthens the magnetic field).
See also the chapter "Magnetic Induction"
Comparison: Permanent magnet vs. electromagnet
- The advantage of an electromagnet over a permanent magnet is that when the coil current is switched off, the magnetic effect almost disappears, i.e. there is no longer any (residual) magnetic effect. For example, electromagnets can be stored without interacting with the environment.
- An electromagnet has a much higher magnetic force compared to a permanent magnet. This can be explained by the coils of the coil and the iron core (which amplify the magnetic field) in the coil.
- The advantage of a permanent magnet is that it does not require an electric current flow to develop a magnetic effect.
Structure of a magnet – permanent magnet / electromagnet – test questions/tasks
1. What is a permanent magnet and how does it retain its magnetic properties?
A permanent magnet is a material that has a lasting magnetic effect. It retains its magnetic properties due to the orientation of the magnetic domains within the material, which remain even after the external magnetic field is removed.
2. What is an electromagnet and how does it work?
An electromagnet is a magnet whose magnetic field is generated by the flow of electric current. The magnetic field disappears when the current flow is stopped.
3. What are the main components of an electromagnet?
An electromagnet consists mainly of the core, which is often made of iron or steel, and the coil, which is wound with electric wire.
4. How does the number of turns affect the strength of an electromagnet?
The number of turns in the coil of an electromagnet affects the strength of the magnetic field. The more turns, the stronger the magnetic field.
5. What happens when the current in an electromagnet is reversed?
When the current in an electromagnet is reversed, the direction of the magnetic field changes.
6. Why do we mainly use iron as the core material in electromagnets?
Iron is mainly used as a core material in electromagnets because it has high magnetic permeability, which means it can amplify the magnetic field.
7. What is meant by magnetic saturation of a permanent magnet?
The magnetic saturation of a permanent magnet refers to the state in which a further increase in the magnetic field does not cause a further increase in magnetization.
8. How are permanent magnets made?
Permanent magnets are made by exposing a magnetizable material to a strong magnetic field, which aligns the magnetic domains of the material and creates permanent magnetism.
9. What types of materials are used to make permanent magnets?
Materials used to make permanent magnets include alnico, ferrite, and rare earth metals such as neodymium and samarium cobalt.
10. How do the poles of a magnet relate to each other?
The poles of a magnet follow the rule that opposite poles (north and south) attract each other and repel equal poles (north-north or south-south).