Permanent magnets

Introduction

A permanent magnet is a type of material with magnetic properties and creates its magnetic field. The materials which are strongly attracted towards a magnet under a certain distance are called ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. Some of them are naturally occurring, like loadstones.

A ferromagnetic material is divided into soft and hard ferromagnetic materials. Soft can be magnetised but not stay magnetised for a long period, whereas hard can be magnetised and stay magnetised for a long time.

Every magnet has its magnetic field and magnetic properties, which shows the magnetic moment of any magnet when placed in a magnetic field.

Ancient people saw that a different type of material (lodestone) attracts a piece of iron toward itself. The word “Magnet” is derived from the Greek word lodestone. They used to suspend loadstone, which was the first magnetic compass. A magnet makes its magnetic field and is responsible for its magnetic fields 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 produced by an external source, it experiences a torque. This torque is proportional to the magnetic moment and the external field. A magnet may also be subjected 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 subjected to no net force, although it is subject to a torque.

Magnetization

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

Characteristics of Magnets

• Attraction: A magnet should always be attracted towards the ferromagnetic material.

• Repulsion: A magnet should always repel the same pole of the magnet, like the north-north poles of a magnet.

• Directive: A magnet, when freely suspended, always points in a north-south direction.

Properties of Permanent Magnets
Some major properties of a permanent magnet show how we can say that a material is a permanent magnet:

• High retentivity – Magnet should be strong and never lose its attractive property.

• High coercivity – Its magnetization should not be affected by extra magnetic fields.

• Permanent poles – A magnet has two poles that are never isolated anyhow; that’s why it works as a compass.

• High permeability – A magnet should always attract a piece of iron and easily magnetise it.

• High flexibility – A magnet should always be easily magnetised and demagnetized without applying any external force on it.

Earlier, we talked about the magnetic field, which is a magnet’s most important property. Now we will know about the magnetic field of a permanent magnet.

Properties of Magnetic Field

• The direction of the magnetic field is always tangential to the field line at any point.

• Magnetic field lines never cross other lines, which is always unique.

• Magnetic field lines are always continuous, forming a closed loop.

• Magnetic field lines always start from the north poles and end at the south poles.

• Magnetic field lines are strong at the poles and weaker at the middle point.

Types of Magnets

A. Permanent Magnet

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

Neodymium Iron Boron(NdFeB)

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

Samarium Cobalt (SmCo)

These are expensive, low mechanical value, easy to reduce, and temperature resistant. e.g. Sm1Co, Sm2Co17, etc.

Alnico

This magnet is formed from three important materials, and by summarising them, it gets the name Alnico(Aluminium+nickel+cobalt). It has good temperature resistance, easily demagnetized, 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, and they are ground from diamond wheels.

B. Temporary Magnets

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.

C. Electromagnet

Electromagnets are made by winding a wire around a soft iron core in a circular loop known as a solenoid. To magnetise it, we have to pass an electric current through the wire to create a magnetic field around it. The strength of the magnetic field depends upon the number of loops and the intensity of the electrical current.

Electromagnets are mostly used in industrial areas, in-home appliances, manufacturing, or recycling processes.

Magnetic Behaviour of a Material

Several forms of magnetic behaviour obtained from the magnetic material:

Ferromagnetic material: These are the materials strongly attracted by the magnet with enough intensity when placed near the magnet. These can also have magnetization properties and can also be a magnet.

Paramagnetic material: These materials are rarely attracted by the magnet, and they can be detected by using a strong magnet or using sensitive instruments, but they don’t show magnetization properties.

Diamagnetic material: These materials are repelled by both the poles of a magnet. Its permeability is less than the permeability of a vacuum. These materials are plastic, copper, carbon, etc.

Common uses of Permanent Magnet

1. Microphone – It works on the principle of the permanent magnet when the coil moves from the magnetic field to produce an electric signal which becomes sound after further processing.

2. Door locks – It works with the help of a strong magnet, often used in commercial or public doors.

3. Engines or generators – are the locations of magnets that also use some electromagnet technology and form electrical energy from mechanical energy and sometimes vice-versa.

Conclusion 

In this section, we learnt about the magnets, types of magnets like a permanent magnet, temporary magnet and electromagnet properties. Further, we also got to know about different types of permanent magnets. We also discussed the magnetization and characteristics of permanent magnets and the behaviour of a material like ferromagnetic material, paramagnetic material, and diamagnetic material. The magnet also produces magnetic field lines, so we also discussed the properties of magnetic field lines and how they are different from other lines, how you will get the direction of any magnetic field lines, and the common use of permanent magnet which helps in your daily life to make our work easier and faster.