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.
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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.
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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.
FAQs on Permanent Magnets And Magnetic Behavior
1. What exactly is a permanent magnet as per the CBSE Class 12 syllabus?
A permanent magnet is a ferromagnetic material that retains its magnetic properties for a long time after the external magnetising field is removed. According to the CBSE 2025-26 syllabus, these materials are characterised by their ability to create a persistent magnetic field without needing a continuous power source. They are created by heating a suitable material above its Curie temperature, placing it in a very strong magnetic field, and then allowing it to cool while the field is maintained, which locks the magnetic domains in a uniform alignment.
2. What are the essential properties a material must have to be a good permanent magnet?
For a material to function effectively as a permanent magnet, it must exhibit specific properties. The two most critical properties are:
- High Retentivity: This is the ability of the material to retain a high level of magnetism even after the external magnetising force is completely removed.
- High Coercivity: This refers to the material's strong resistance to being demagnetised by opposing magnetic fields, physical shocks, or high temperatures.
Essentially, a good permanent magnet is easy to magnetise but very difficult to demagnetise.
3. How does the magnetic behaviour of permanent magnets differ from that of temporary magnets or electromagnets?
The key difference lies in their ability to retain magnetism. Permanent magnets are made from 'hard' ferromagnetic materials (like steel or Alnico) that have high retentivity and stay magnetised indefinitely once magnetised. In contrast, temporary magnets, such as electromagnets, are made from 'soft' ferromagnetic materials (like soft iron). They exhibit strong magnetic behaviour only when an electric current flows through a surrounding coil, creating a magnetic field. As soon as the current stops, they lose almost all their magnetism.
4. What are some common examples of permanent magnets and their real-world applications?
Permanent magnets are integral to many modern technologies. Here are some key examples:
- Alnico Magnets: An alloy of aluminium, nickel, and cobalt. Used in electric motors, guitar pickups, and sensors.
- Ferrite (Ceramic) Magnets: Made from iron oxide and strontium carbonate. Commonly used in refrigerator magnets, speakers, and small DC motors.
- Neodymium Magnets (NdFeB): Extremely strong magnets made from an alloy of neodymium, iron, and boron. Found in computer hard drives, high-end headphones, electric vehicles, and MRI machines.
- Samarium-Cobalt Magnets (SmCo): Known for their high-temperature resistance, they are used in aerospace, military applications, and turbo-machinery.
5. Why does a permanent magnet lose its magnetic behaviour if it is heated or hammered?
A permanent magnet loses its magnetism under these conditions due to the disruption of its internal structure. Magnetism arises from the uniform alignment of tiny regions called magnetic domains.
- Heating: Provides thermal energy, causing the atoms to vibrate vigorously. If heated above a critical point known as the Curie temperature, the vibrations become so intense that they randomise the alignment of the magnetic domains, destroying the net magnetism.
- Hammering: Provides strong mechanical energy that physically jars the domains out of alignment, causing the material to lose its magnetic properties.
6. How does the hysteresis loop help explain the behaviour of a permanent magnet?
The hysteresis loop is a graph that shows a material's magnetic response (B) to an external magnetising field (H). For a permanent magnet, the ideal loop is both tall and wide. The height of the loop on the B-axis when H is zero represents its retentivity (how much magnetism it retains). The width of the loop on the H-axis shows its coercivity (how much opposing field is needed to demagnetise it). Therefore, a wide and tall hysteresis loop is a clear indicator that the material is suitable for making a strong and durable permanent magnet.
7. What makes materials like Neodymium so much stronger than common magnets like Ferrite?
The exceptional strength of magnets like Neodymium (NdFeB) stems from their unique atomic-level crystalline structure. This structure creates a very high magnetic anisotropy, which means its magnetic domains have an extremely strong preference to align in one particular direction. This perfect alignment and the strong coupling between atoms make it very difficult to divert them from this direction. Consequently, the material can sustain a very high level of magnetisation (high retentivity) and strongly resist demagnetising forces (high coercivity), resulting in a significantly more powerful external magnetic field compared to materials like Ferrite.
