Permanent Magnets And Magnetic Behavior

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What is a Permanent Magnet?

The objects, called magnets, produce the magnetic field. When these magnetism properties are not lost throughout time, it is called a permanent magnet. So what is the individual property in a permanent magnet that is not lost when subjected to the test of time?

Magnetism is also represented by ferromagnetic material. A few of the materials are some alloys of nickel and iron. The orientation of domains in a ferromagnetic substance depends on its magnetism property.

The magnetic fields produced individually withdraw themselves out when the domains are oriented randomly. A collective magnetic field can be formed by reducing the domain randomization by influencing it with an electrical field. This is one of the processes on how the electromagnets are produced. However, if the domains are already arranged in a way they point in the same direction, they will produce a collective magnetic field even without using an external influence. These are known as permanent magnets.

Let us have a look at some permanent magnets and magnetic behaviour.

Magnetism and Magnetic Behaviour

When a magnetizing field is imposed on ferromagnetic substances, the domains get arranged to produce magnetism, and they do not go back to their normal state. When the driving field results as zero, and then the domains have not even rearranged themselves to normalcy, the substances at that time takes to demagnetize or remains magnetized for is called remanence. If we try to assign the magnetic property back to zero by applying a field in the opposite direction, the reverse field amount that is required to demagnetize that substance is called coercivity. The lack of retaining the magnetic property of a substance is called hysteresis.

Didn't we notice that an iron nail attached to a magnet sometimes attracts other non-magnetic iron nails for a short time even after it has been detached from the magnet? This happens because the iron nail domains had been reoriented. This effect is weak, and pretty soon, it will be lost. Therefore, the corresponding iron nail will not be considered as a permanent magnet.

The primary advantage of a permanent magnet over any other magnet type is, it does not require a continuous supply of external energy (for electromagnets, electricity) to exhibit magnetism. For example, we shall use permanent magnets as compass needles.

Example of a Permanent Magnet

A refrigerator magnet is an everyday example of a permanent magnet. The image given below shows the magnetic field produced by a bar magnet. The magnetic field is the sphere of the magnet influence.

(Image to be added soon)

It can be visualized by sprinkling the iron filings on a bar magnet. The filings themselves will arrange on the lines of the magnetic field of the magnet used. The strength of various magnets can be seen physically in the same way.

Types of Permanent Magnets

Let us dig deeper into a few types of permanent magnets.

  • Magnetic Metallic Elements

Most of the materials have unpaired electron spins, and almost all of these material types are paramagnetic. When the interaction between the spins occurs in such a manner that the spins align spontaneously, the materials are known as ferromagnetic (what is loosely often termed as magnetic). Due to the way their regular atomic structure of crystalline causes their spins to interact, a few metals are ferromagnetic when found in their natural states, as ores. These include iron ore (lodestone or magnetite ), nickel, cobalt, and the rare earth metals gadolinium and dysprosium (at a very low temperature).

Such type of naturally occurring ferromagnets were used in the first experiments, including magnetism. However, the technology has expanded the magnetic material's availability to include various man-made products, based on the naturally magnetic elements.

  • Rare-Earth Magnets

Rare earth (lanthanoid) elements have an 'f' electron shell (which can accommodate up to 14 electrons), which is occupied partially. These electrons spin can be aligned, resulting in powerful magnetic fields, and these elements, therefore, are used in high-strength compact magnets where their higher price is not a concern. The most common rare-earth magnet types are neodymium-iron-boron (NIB), and samarium-cobalt magnets.

  • Single-Chain Magnets (SCMs) and Single-Molecule Magnets (SMMs)

These were discovered in the 1990s, that particular molecules containing paramagnetic metal ions can store a magnetic moment at very low temperatures. These are entirely different from the conventional magnets that store information at a magnetic domain level and could provide a far denser storage medium theoretically than the conventional magnets.

The representation of an Ovoid-shaped magnet (possibly, Hematine), one hanging from the other, is given below.

(Image to be added soon)

The Main Attributes of SMM are Given Below

  • A Negative value of the zero-field splitting (D) anisotropy

  • A Significant ground state spin value (S), provided by ferrimagnetic or ferromagnetic coupling between the paramagnetic metal centres

Most SMMs have manganese, but can also be found with iron, vanadium, cobalt, and nickel clusters. It has been very recently found that some of the chain systems can also represent a magnetization that persists at higher temperatures for long times. These systems have been referred to as single-chain magnets.

FAQ (Frequently Asked Questions)

1. What Makes a Substance Magnetic?

The atomic electron orbitals usually are either d- or f-states with sizeable angular momentum (and significant magnetic moments thereby) that get lined up along crystal axes and interacts with each other in a manner to favor alignment in either same direction (ferromagnetism) or opposite directions (antiferromagnetism, usually exhibits no or fragile "magnetic" properties).

The electron's spin (which has their own magnetic moment) sometimes interact ferromagnetically (more often antiferromagnetically) to produce a type (usually weaker) of magnetism.

Also, there is nuclear [anti] ferromagnetism (at extremely low temperatures), due to the magnetic moments of nuclei, which are about 2000 times typically weaker than that of electrons. However, what we usually recognize as "magnetic" properties are exclusively due to electrons.

2. Why Does the Earth Behave Like a Magnet?

There are many reasons why the earth behaves like a magnet, and the well-known ones are listed below.

  1. The earth's magnetic field is not just a kind of permanent magnet. It means it is a magnetized material with a persistent magnetic field. (Considering the changing pattern of geomagnetism over ten thousand years and evidence of Magnetic pole Reversal of planet before thousands of years)

  2. The geomagnetic field, as GEODYNAMO, can be described better in the picture given below.

(Image to be added soon)

Here, the elements (a, b, c) of the above figure can be explained as:

    1. An electrically conductive fluid (the liquid Iron core of the outer core of the planet) induced by convection

    2. Kinetic energy due to the rotation of planet cause liquid Iron convection resulting in field induction

    3. Organisation of electric current and fluid motions (liquid Iron) into columns parallel to the rotation axis resulting in the Induction of GEOMAGNETISM. The magnitude of the magnetic field ranges from 25 to 65 microteslas over the surface, and the Magnetic pole tilted with ~11 degrees with the Rotation axis of the planet.

  1. Extending from the interior of the planet to space up to magnetosphere up to tens of thousands km to space - Protection from high energy Solar wind and Cosmic rays.

An Electric Conductive Convecting Fluid (within the Body Surface) Dipole, a Rotating Cause Magnetic Field of Celestial Body.