IMANTATION: WHAT IT CONSISTS OF, METHOD AND EXAMPLES - PHYSICAL - 2025

The magnetisation or magnetisation is a vector quantity that is also known as magnetization vector strength. It is denoted as M and is defined as the magnetic moment m per unit volume V. Mathematically it is expressed as follows:

M = d m / dV

Units M in the International System of Units SI are ampere / meter, the same as those of the magnetic field H. The notation in bold type is to indicate that these are vectors and not scalars.

Figure 1. Ferrite magnets in the form of rings. Source: Wikimedia Commons.

Now, the magnetic moment of a material or substance is the manifestation of the movement of electric charges inside the atom, fundamentally that of the electron.

In principle, the electron inside the atom can be imagined as a tiny closed circuit of current, while it describes a circular orbit around the nucleus. In reality, the electron does not behave in this way according to the quantum-mechanical model of the atom, but it coincides with this in terms of the magnetic effect.

In addition, the electron has a spin effect, analogous to a rotation on itself. This second movement produces an even more important contribution to the total magnetism of the atom.

When a material is placed within an external magnetic field, the magnetic moments of both contributions align and create a magnetic field within the material.

Magnetization methods

Magnetizing a material means giving it magnetic properties, either temporarily or permanently. But the material must respond appropriately to magnetism for this to happen, and not all materials do.

Depending on their magnetic properties and the response they have to an external magnetic field such as that of a magnet, materials are classified into three large groups:

-Diamagnetic

-Paramagnetic

-Ferromagnetic

All materials are diamagnetic, whose response consists of a weak repulsion when placed in the middle of an external magnetic field.

For its part, paramagnetism is typical of some substances, which experience a not very intense attraction to an external field.

However, ferromagnetic materials are those with the strongest magnetic response of all. Magnetite is an iron oxide that is a natural magnet known from ancient Greece.

Figure 2. Magnetite or lodestone from Brazil. Source: Wikimedia Commons.

The magnetization methods that will be described below make use of materials with good magnetic response to achieve the desired effects. But at the nanoparticle level, it is even possible to magnetize gold, a metal that usually does not have a remarkable magnetic response.

How to magnetize a ferromagnetic object?

Unless the material is a natural magnet, such as a piece of magnetite, it is generally demagnetized or demagnetized. This leads to another classification of magnetic materials:

- Hard, which are permanent magnets.

- Soft or sweet, which although they are not permanent magnets, have a good magnetic response.

- Semi - hard, possessing intermediate properties among the above.

The magnetic response of ferromagnetic materials is due to the fact that the magnetic domains are arranged inside them, regions with randomly arranged magnetization vectors.

This results in the magnetization vectors being canceled and the net magnetization being zero. For this reason, to create a magnetization, the magnetization vectors must be aligned, either permanently or at least for a time. In this way the material is magnetized.

There are a number of ways to achieve this, for example by induction magnetization, contact, rubbing, cooling, and even hitting the object, as detailed below.

Examples

The selected magnetization method depends on the material and the objectives of the procedure.

Artificial magnets can be created for a wide variety of functions. Today magnets are industrially magnetized, following a very careful process.

Induction magnetization

By this method, the material to be magnetized is placed in the middle of an intense magnetic field, such as that of a powerful electromagnet. In this way the domains and their respective magnetizations are immediately aligned with the external field. And the result is that the material is magnetized.

Depending on the material, it can retain the magnetization thus obtained permanently, or it can lose it as soon as the external field disappears.

Rubbing magnetization

This method requires rubbing one end of the material to be magnetized with the pole of a magnet. It must be done in the same direction, so that in this way the rubbed area acquires the opposite polarity.

This creates a magnetic effect, in such a way that at the other end of the material, a contrary magnetic pole is created, resulting in the substance being magnetized.

Contact magnetization

In contact magnetization, the object to be magnetized must come into direct contact with the magnet, so that it acquires its magnetization. The alignment of the domains in the object to be magnetized occurs as a cascade effect, coming from the end in contact to the other end quickly.

A typical example of contact magnetization is to attach a clip to a permanent magnet, and the magnet will become magnetized, attracting other clips to form a chain. It also works with nickel coins, nails, and bits of iron.

But once the first clip, nail or coin is removed from the magnet, the magnetization of the others disappears, unless it is a truly strong magnet capable of producing permanent magnetization.

Electric method to magnetize

The material to be magnetized is wrapped in conductive wire through which an electric current is passed. Electric current is nothing more than a moving charge that produces a magnetic field. This field is responsible for magnetizing the material placed inside and the effect is to greatly increase the resulting field.

The magnets thus created can be activated and deactivated at will, simply by disconnecting the circuit, in addition to the fact that the power of the magnet can be modified by passing more or less current. They are called electromagnets and with them you can easily move heavy objects or separate magnetic from non-magnetic materials.

Magnetization by a blow

An iron rod or even a metal filing cabinet can be magnetized by striking it inside in a magnetic field. In some localities, the Earth's magnetic field is strong enough to achieve this effect. An iron bar that strikes the ground vertically can become magnetized because the Earth's magnetic field has a vertical component.

Magnetization is checked with a compass that is placed on top of the bar. For a filing cabinet, it is enough to open and close the drawers with sufficient determination.

A blow can also demagnetize a magnet, as it destroys the order of the magnetic domains within the material. Heat also has the same effect.

Magnetization by cooling

There are substances such as basalt lavas in the interior of the Earth, which when cooled in the presence of a magnetic field, retain the magnetization of said field. Examining these types of substances is evidence that the Earth's magnetic field has changed its orientation since the Earth was created.

References

1. Figueroa, D. (2005). Series: Physics for Science and Engineering. Volume 6. Electromagnetism. Edited by Douglas Figueroa (USB).
2. Hewitt, Paul. 2012. Conceptual Physical Science. 5 ^th. Ed. Pearson.
3. Kirkpatrick, L. 2007. Physics: A Look at the World. 6 ^ta Editing abbreviated. Cengage Learning
4. Luna, M. Did you know that gold can be a magnet? Recovered from: elmundo.es.
5. Tillery, B. 2012. Physical Science. McGraw Hill.