Permanent Magnets

A permanent magnet is a type of material that has its own magnetic properties and creates its own magnetic field. Materials such as iron, steel, nickel, cobalt etc., that are strongly attracted towards a magnet within a certain distance are called ferromagnetic. Some of them are naturally occurring, like loadstones. A ferromagnetic material is divided into two parts: Soft ferromagnetic material and hard ferromagnetic material. Soft ferromagnetic material can be magnetised but will not stay magnetised for a long period of time, whereas hard ferromagnetic material can be magnetised and stays magnetised for a long time. Every magnet has its own magnetic field and magnetic properties, which show the magnetic moment of any magnet when placed in an electric field.

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The discovery of magnets happened when ancient people saw that a different type of material (lodestone) attracts a piece of iron toward itself. The word “magnet” is obtained from the Greek word for lodestone – they used to suspend lodestones which were the first magnetic compasses. A magnet makes its own magnetic field and is responsible for its magnetic field lines. The strength of the magnetic field at any particular point is directly proportional to the magnitude of its magnetic moment. When the magnet is in an external magnetic field, which is produced by an external source, it is known as torque. This is oriented towards the magnetic moment and parallel to the field. The amount of this torque is proportional to the magnetic moment and the external field. A magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the magnet and source. If the field is uniform in space, the magnet is subject to no net force, although it is subject to a torque.

Magnetisation:-

Magnetisation is a property of magnetic material. It is also known as magnetic moment per unit volume and is represented by M. Iron can be magnetised by around a million amperes per metre.

Characteristics of magnet:-

1:- Attraction:- A magnet should always be attracted towards ferromagnetic material. 2:- Repulsive:- A magnet should always repel the same pole of another magnet, like two north-north poles of magnets. 3:- Directive:- A magnet, when freely suspended, always points in the north-south direction. Properties of permanent magnets:- There are some major properties of a permanent magnet that show that a material is a permanent magnet:- 1:- High retentivity:- Magnet should be strong and never lose its attractive property until an external force is applied. 2:- High coercivity:- Its magnetisation should not be affected by extra magnetic fields. 3:- Permanent poles:- A magnet has two poles that are never isolated – that’s why it worked as a compass. 4:- High permeability:- A magnet should always attract a piece of iron and easily magnetise it. 5:- High flexibility:- A magnet should always be easily magnetised and demagnetised without applying any external force to it. Earlier, we talked about magnetic fields – which is an important property of every magnet – let us now learn about the magnetic field of a permanent magnet. Properties of magnetic field:- 1:- The direction of the magnetic field is always tangential to the field line at any point. 2:- Magnetic field lines never cross other lines, which means they are always unique. 3:- Magnetic field lines are always continuous, so they can form a closed loop. 4:- Magnetic field lines always start from the north poles and end at the south poles. 5:- Magnetic field lines are strong at the poles and weaker at the middle point. Types of Magnet:- There are many types of magnets, but here, we shall specifically discuss the three most important types of magnets:-

Permanent magnet:-

These are materials found naturally, and once they are magnetised, they work as a magnet for a long period of time. There are four types of permanent magnets:-

Neodymium Iron Boron(NdFeB):-

This type of magnet is found rarely on earth and has high coercive force, low mechanical strength and low corrosion resistance if it is opened. e.g. gold, iron etc.

Samarium Cobalt (SmCo):-

These are expensive, have low mechanical value, are easy to reduce and have temperature resistance – for example, SmCo5, Sm2Co17 etc.

Alnico:-

This magnet is formed from three important materials, and it gets the name Alnico by summarising their names (Aluminium+nickel+cobalt). It has good temperament resistance, is easily demagnetised and also has other properties like other rare earth materials.

Ceramic or Ferrite:-

These magnets are made from iron oxide, strontium carbonate and ceramic. It is brittle in nature, and they are grinded from diamond wheels.

Temporary magnet:-

These magnets can vary in composition; sometimes, they behave like a permanent magnet and sometimes, they can’t. Especially when they are placed in a magnetic field, they act as a magnet.

Electromagnet:-

Electromagnets are made by winding a wire around a soft iron core in a circular loop, basically known as a solenoid. To magnetise a solenoid, an electric current is passed through the wire to create a magnetic field around it. The strength of the magnetic field totally depends upon the number of loops and the intensity of electrical current. Electromagnets are mostly used in industrial areas, in home appliances, in manufacturing or recycling processes.

Magnetic behaviour of a Material:-

Several forms of magnetic behaviour are observed from magnetic material:- Ferromagnetic material:- These are materials that are strongly attracted by magnets with enough intensity when placed near the magnet. These can also have magnetisation properties and can also be a magnet. Paramagnetic material:- These materials, which are rarely attracted by magnets, can be detected by using a strong magnet or sensitive instruments, but they don’t show magnetisation. Diamagnetic material:- These materials are repelled by both the poles of a magnet. Their permeability is less than the permeability of vacuum. These materials include plastic, copper, carbon, etc. Common uses of permanent magnets:- 1:- Microphone:- It works on the principle of a permanent magnet. When a coil moves from a magnetic field, it produces an electric signal which becomes sound after further processing. 2:- Door locks:- It works with the help of a strong magnet and is often used in commercial or public doors. 3:- Engines or Generators:- These are some of the best applications of magnets, which also use some electromagnetic technology and form electrical energy from mechanical energy and sometimes vice-versa.

Conclusion

Through this study material, we got to know about magnets and their discovery. We also learnt about the different types of magnets like permanent magnets, temporary magnets and electromagnets, along with their properties. Further, we also got to know about different types of permanent magnets. We also discuss the magnetisation and characteristics of permanent magnets and the behaviour of materials like ferromagnetic material, paramagnetic material and diamagnetic material. Magnets also produce magnetic field lines, so we also discuss the properties of magnetic field lines and how they are different from other lines. We learn about how you will get the direction of any magnetic field lines, the common use of permanent magnets and how they help in our daily lives and make our work easier and faster.

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