How Does Magnetism Work & Do Magnets Lose Their Strength?

Magnets have captivated human curiosity for centuries, offering a fascinating glimpse into the invisible forces that shape our world. This guide delves into the fundamental principles of magnetism, exploring the mechanisms that govern its behaviour. From understanding the origins of magnetism to knowing what factors contribute to magnetic strength, we take a closer look at these fascinating objects that are used in all walks of life, day to day.

How do magnets work?

Magnets work because of tiny particles called electrons. These electrons spin and create small magnetic fields. In most things, these fields cancel out. However, in certain materials, like iron, the tiny magnetic fields align in the same direction.

When we rub a magnet on these materials or expose them to a magnetic field, it makes the magnetic fields line up. This alignment makes a magnetic force, creating a north and south pole. Like poles repel, and opposite poles attract. This simple alignment turns the material into a magnet, and it can attract or repel other magnets or magnetic materials.

What causes magnetism?

Magnetism arises from the alignment of atomic magnetic moments within the material. At the microscopic level, each atom behaves like a tiny magnet due to the magnetic properties of its electrons.

In ferromagnetic materials such as iron, nickel, and cobalt, neighbouring atomic magnets spontaneously align, forming regions called magnetic domains.

In an unmagnetised state, these domains point in random directions, cancelling out each other’s magnetic effects. But when exposed to an external magnetic field, the domains can align, creating a collective and stronger magnetic field. This alignment persists even after removing the external field, resulting in a magnetised material.

Why do magnets attract and repel?

Magnets attract and repel due to the alignment of magnetic domains within their structure. In a magnetised material, microscopic regions called magnetic domains have aligned magnetic moments. When two magnets are brought together, their domains interact. If the aligned domains of both magnets point in the same direction, they attract each other, enhancing the overall magnetic field.

However, if the domains point in opposite directions, they repel. This behaviour arises from the fundamental property of magnetic dipoles and the magnetic force between them, as described by the laws of magnetism in physics.

Can a magnet lose its strength?

Despite their resilience, magnets can experience a gradual loss of strength known as demagnetisation. One common cause is exposure to elevated temperatures, which can disrupt the alignment of magnetic domains within the material.

Physical shock or vibration may also affect the alignment, impacting the overall magnetism. Additionally, magnets can gradually lose their strength through a process called demagnetisation, where the magnetic domains revert to a more random orientation. This can occur through exposure to strong opposing magnetic fields or by repeated use in certain applications. In some materials, environmental factors such as humidity and corrosion can also contribute to a decline in magnet strength.

While permanent magnets generally retain their properties well, external influences and environmental conditions can lead to a gradual loss of magnetic strength.

Factors which cause magnets to demagnetise

Understanding the factors that are likely to demagnetise a magnet is essential for preserving the integrity and functionality of magnets over time. While we have touched upon a few above, some of the most common ways in which this can occur include:

• Heat: Exposure to high temperatures can cause the atoms within a magnet to vibrate more vigorously, disrupting the alignment of magnetic domains. The Curie temperature is the temperature at which a material loses its magnetic properties, and exceeding this temperature can lead to demagnetisation.
• Physical damage: Strong impacts or dropping of a magnet can cause its internal structure to change, leading to a loss of magnetic strength. Physical damage can also cause the magnetic domains to become misaligned.
• Electromagnetic fields: Strong external magnetic fields can interfere with the alignment of magnetic domains in a magnet, causing it to lose its magnetism. This is particularly true for magnets made of materials with lower coercivity (ability to resist demagnetisation).
• Time: Even without external factors, magnets can naturally lose their strength over time due to a phenomenon known as ageing. The magnetic domains within a material can slowly become disordered, leading to a gradual decrease in magnetic strength.

It’s important to note that the rate at which a magnet loses its strength depends on the specific type of magnet, its composition, and the conditions to which it is exposed.

Magnets made of different materials may have varying levels of resistance to demagnetisation. For instance, neodymium magnets are the strongest type of permanent magnets commercially available. While they are very powerful, they are more susceptible to demagnetisation compared to some other types. On the other hand, samarium cobalt magnets have excellent resistance to demagnetisation and can maintain their magnetic strength at high temperatures.