Introduction:
One of the most interesting and useful forces of nature is magnetism. Since the compass needle that led the early mariners, the strong electro-magnets that lift steel weights in modern scrap yards, magnetism runs through almost every department of scientific enquiry and human technology.
Every magnet, natural or man-made, is based on one basic principle, namely the alignment of microscopic-level magnetic domains of a material. The way in which these domains are created and how they are controlled results in the creation of the two major types of magnets: permanent magnets and electromagnets.
Despite the fact that both types have magnetic properties, they are very different regarding manufacturing industry, mechanism of operation and their application. This paper gives an in-depth comparison of each of these types and contrasts their properties, composite materials, and applications with reference to Figure and Table.
What Are Permanent Magnets?
These materials maintaining their magnetic properties after the external magnetic field has been removed are known as permanent magnets. That is, they do not lose their magnetization during long durations even at room temperatures.
A permanent magnet can hence be described as follows:
A substance that retains its ferromagnetic property after a long period of time after magnetization is known as a permanent magnet.
The materials are notable in that the atomic magnetic moments the dipole moments which are attributed to an electron do not align and require no external current or magnetic field.
Examples of them include steel, alnico (alloy of aluminium, nickel and cobalt), cobalt steel and ticonal. These materials have a high retentivity which is a characteristic of their ability to maintain magnetization and high coercivity which are the characteristic of their resisting to demagnetization.
Common everyday uses include refrigerator magnets, compasses, electric motors, and microphones — devices that rely on a stable, continuous magnetic field.
How Permanent Magnets Are Made
Permanent magnets can be made in several ways — some quite ancient, others highly scientific.
1. The Blacksmith’s Technique
Its classical approach is more than four hundred years old. According to Figure 1, a blacksmith could make a permanent magnet by heating a rod of iron to redness and hammering it many times as he holds it in the northsouth position.
Hammer blow slightly by slightly aligning the magnetic domains in the iron of the magnetic field of the earth. In many strokes, the domains start to be mostly aligned towards one direction, thus creating a weak but permanent magnet.
William Gilbert, who in the year 1600 published one of the first scientific studies of magnetism, De Magnete, described this method in an attempt to stay famous. Gilbert's experiments provided the background of how to achieve the control of the magnetic alignment by mechanical activities and thermal processes.
2. Magnetization Using a Solenoid
In modern practice, magnets are usually made by putting a rod of ferromagnetic material (such as steel) inside a solenoid, a cable of wire and a significant electric current through it.
The rod is magnetized by the magnetic field produced by the solenoid and it is oriented in one direction. Upon further switching off of the current, the rod remains permanently magnetized.
This is more effective and controllable than the technique used by the blacksmith, allowing the manufacturer to make the magnets with more defined strengths and polarities.
Material Requirements for a Good Permanent Magnet
The performance of a permanent magnet depends largely on the magnetic properties of the material used. These properties can be understood through the hysteresis curve, shown in Figure 5.14.
A hysteresis curve plots the variation of magnetic induction (B) with magnetizing field strength (H). The shape of this loop reveals how easily a material can be magnetized and demagnetized.
To make a good permanent magnet, a material should have:
- High retentivity: So that it retains a strong magnetization even after the external field is removed.
- High coercivity: So that the magnetization is not lost due to stray magnetic fields, temperature fluctuations, or mechanical shocks.
- Moderate permeability: Excessive permeability may make the magnet easy to magnetize but also easy to demagnetize.
- Thermal and mechanical stability: To ensure long-term reliability in practical environments.
Steel is a classic example — it has lower permeability than soft iron but higher coercivity, making it ideal for permanent magnets.
Modern magnets like alnico and ticonal are engineered alloys optimized for high coercivity and retentivity, allowing them to remain magnetized even under harsh conditions.
What Are Electromagnets?
Unlike permanent magnets, the electromagnets acquire their magnetism through an electric current. They are only magnetic when an electric current passes through a coil that is wrapped around a soft iron core.
This means that, modulation of the electric current can be used to control the operation state of an electromagnet. Magnetic field intensity is directly proportional to the current size and the amount of turns in the coil.
The soft iron core in Figure 2 also forms part of an electromagnet, and it is located in a solenoid. When current is passed through the coil, the soft iron is highly magnetized, and thus creates magnetic poles in its ends. At the time the current is discharged the core is nearly demagnetized.
These properties have made electromagnets especially useful in areas that need to have the magnetic field controlled such as cranes, relays and electric bells.
Working Principle of an Electromagnet
The principle of electromagnet is simple yet effective. When electric current is carried down a conductor it produces a magnetic field around the conductor. When the conductor is configured to be a coil, the fields of each turn add together and a powerful near uniform field of a magnet is produced inside the coil.
The magnetic flux density is dramatically enhanced (by a thousandfold or more) by the insertion of a soft-iron core into the solenoid. The soft-iron is allotted magnetism by arranging the magnetic domains in the flow of the field that is applied.
As the current is switched off, the domains also go back to randomized orientations and the resulting magnetization disappears. This is due to the low value of retentivity of soft-iron, which is a preference to cores of an electromagnet.
An electromagnet may therefore be used as a magnet-on-demand whereby its strength and polarity are easily controllable.
Material Requirements for Electromagnets
For an electromagnet to be efficient, the material used for its core must magnetize quickly and lose magnetism equally quickly when the current ceases.
The ideal properties are:
- High permeability: So that the material can produce a strong magnetic field with small current.
- Low retentivity: So that it does not remain magnetized when the current is switched off.
- Low hysteresis loss: To prevent energy waste during rapid magnetization and demagnetization cycles (as in AC devices).
Soft iron fits these requirements perfectly. Its hysteresis loop (as shown in Figure 5.14) is narrow, indicating minimal energy loss. This is crucial for transformers, telephone diaphragms, and other alternating-current applications.
When used in transformers, low-hysteresis materials reduce heat generation and improve efficiency. To further minimize energy loss, laminated cores are often used to reduce eddy current formation.
Comparison: Permanent Magnets vs Electromagnets
Although both types produce magnetic fields, their differences are significant. Table provides a concise comparison:
| Property | Permanent Magnet | Electromagnet |
|---|---|---|
| Source of magnetism | Alignment of magnetic domains | Electric current through a coil |
| Magnetic strength | Fixed, determined by material | Variable, depends on current and turns |
| Retentivity | High | Low |
| Permeability | Moderate | High |
| Magnetization control | Not possible | Easily controlled via current |
| Heating loss | Negligible | Present, especially in AC use |
| Typical materials | Steel, alnico, cobalt steel | Soft iron |
| Applications | Compasses, motors, microphones | Cranes, relays, transformers, bells |
This table highlights the central idea: permanent magnets offer stability, while electromagnets offer control.
Permanent magnets require no power but have a fixed magnetic strength. Electromagnets, by contrast, can be made incredibly powerful and easily manipulated, but they depend on continuous electric energy.
Applications of Permanent Magnets
Permanent magnets are also used where a magnetic field with constant strength is needed but it does not need constant power supply. Important applications are:
- Electric motors and dynamos: They provide a static magnetic field that is required in changing electrical energy into mechanical motion.
- Microphones and loudspeakers: Permanent magnets are used to convert electrical signals to acoustic waves by interacting with current-carrying coils.
- Magnetic compasses: They follow the magnetic field of the earth so as to show the geographic direction.
- Magnetic locks and latches: Magnetic locks and fasteners are used on doors, cabinets and electronic devices to offer contact free locking.
- Refrigerator magnets and toys: This is a typical example of a static magnetic field that are often found in cooling appliances and other recreational products.
Permanent magnets can especially be used in small-scale and low-maintenance devices due to their natural reliability and non-dependence on other sources of auxiliary power.
Applications of Electromagnets
Electromagnets, which have controllable magnitude, have transformed modern day technology.
- Industrial lifting: Electromagnets of large scale are used in crane systems to lift and move scrap iron, steel plates and bulk ferromagnetic materials.
- Transformers and relays: A transformer works on the principles of electromagnetism to transfer electrical energy between high-voltage circuits with a very low resistance.
- Electric bells and buzzers: This is based on the attraction and release of striker or armature in a cyclic manner.
- Telephones and loudspeakers: When the current flowing through the magnetic coil changes over time, diaphragm vibrations are caused, and therefore the electrical signal is converted to acoustic waves.
- Magnetic separation: It is used in the recycling industries to select magnetic components amongst non-magnetic components.
- Medical applications: There are vital roles played by electromagnets in magnetic resonance imaging machines and magnetic treatment machines.
Their ability to produce large magnetic fields in a flash - and to shut them off with no less ease - makes electromagnets essential in both large industry and fine instrumentation.
Energy Considerations and Efficiency
One of the main differences between permanent magnets and electromagnets is associated with the energy consumption.
When permanent magnets are magnetized, they do not need external energy to maintain a magnetic field. Electromagnets on the other hand are constantly using energy to sustain their magnetism.
The performance of electromagnets depends on the reduction of losses related to hysteresis and eddy current:
- Hysteresis: The loss of energy to heat is hysteresis, and every magnetic cycle of magnetization and demagnetization leaves some energy behind; the hysteresis loop is narrow in soft iron, reducing this loss.
- Eddy currents: These are circulating currents induced in the core material and produce heat; the effect is reduced by the use of laminated cores or high-resistance materials.
In alternating current equipment like transformers, it is important to reduce the hysteresis and eddy current losses to achieve the most performance.
In comparison, permanent magnets have a zero loss of energy but cannot change the magnetic strength; hence, there is a trade-off of efficiency versus flexibility.
Key Takeaways and Conclusion
Both permanent magnets and electromagnets have distinct advantages, shaped by the materials from which they are made and the physics of their magnetism.
| Feature | Permanent Magnet | Electromagnet |
|---|---|---|
| Power requirement | None after magnetization | Requires electric current |
| Field strength | Fixed | Adjustable |
| Magnetic retention | Long-lasting | Temporary |
| Typical material | Hard steel, alnico | Soft iron |
| Example use | Compass, motor | Crane, transformer |
Permanent magnets represent stability and simplicity — once magnetized, they serve for years without maintenance. Electromagnets represent control and strength — capable of generating massive magnetic fields at the flick of a switch.
The choice between them depends entirely on the application:
- Use permanent magnets when you need a constant field and zero power consumption.
- Use electromagnets when you need adjustable or intermittent fields.
From the humble blacksmith hammering red-hot iron as in Figure 1, to the powerful electromagnets lifting tons of metal as shown in Figure 2, humanity’s mastery over magnetism continues to shape the modern world.
Magnetism remains, even today, one of nature’s most versatile and captivating forces — invisible yet indispensable.