Magnetism is a fundamental force of nature that allows objects to attract or repel each other. It is a physical phenomenon intrinsically linked with moving electricity and characterized by fields of force.
Understanding Magnetic Fields and Poles
Magnets exert their influence through an invisible magnetic field that surrounds them. When iron filings are sprinkled near a magnet, they align along these lines, making the field pattern visible.
Every magnet possesses two distinct regions called poles: a North pole and a South pole. Magnetic field lines emerge from the North pole and enter the South pole, forming continuous loops. Opposite poles attract each other, while like poles repel. For instance, a compass needle’s North pole points towards Earth’s magnetic South pole.
The Microscopic World of Magnetism
Magnetism originates at the atomic level from the movement of electrons within atoms. Electrons, as charged particles, create tiny magnetic fields as they move. This motion includes their “spin” and orbital motion around the atomic nucleus. Each electron possesses a small magnetic moment, acting like a miniature magnet.
In most materials, these atomic magnetic moments are randomly oriented, causing their magnetic effects to cancel out. These materials therefore do not exhibit overall magnetic properties. However, in certain substances, such as ferromagnetic materials, these tiny magnetic moments align in the same direction within microscopic regions called magnetic domains.
A magnetic domain is a small area where the magnetic moments of many atoms are uniformly aligned, creating a net magnetization within that region. When a material is unmagnetized, these domains are oriented randomly, resulting in no overall magnetic field. When an external magnetic field is applied, these domains can rotate and align with the external field, leading to the material becoming magnetized.
Categories of Magnetic Materials
Substances interact with magnetic fields in different ways. These differences stem from the behavior of electrons within their atoms and how they respond to an external magnetic field. The three main types are ferromagnetism, paramagnetism, and diamagnetism.
Ferromagnetic materials, such as iron, nickel, and cobalt, are strongly attracted to magnets and can become permanently magnetized. Their magnetic domains align and remain aligned even after an external magnetic field is removed, resulting in a strong, lasting magnetic effect.
Paramagnetic materials, including aluminum and platinum, are weakly attracted to magnetic fields. These materials have unpaired electrons, which possess magnetic moments that temporarily align with an external field. However, this alignment is temporary, and their magnetic properties disappear once the external field is removed. The paramagnetic effect is typically much weaker than ferromagnetism.
Diamagnetic materials, such as water, copper, and bismuth, exhibit a weak repulsion from a magnetic field. This repulsion arises from a slight reorientation of electron orbits induced by the external field, creating a magnetic moment that opposes the applied field. While all materials possess some degree of diamagnetism, this effect is often masked by stronger paramagnetic or ferromagnetic properties if those are present.
How Magnetism Can Change
The magnetic properties of a substance, particularly ferromagnetic materials, are not always permanent and can be altered or destroyed by various factors. One significant factor is heat, which can disrupt the alignment of magnetic domains. Heating a ferromagnetic material above a specific point, known as its Curie temperature, causes it to lose its permanent magnetic properties and become paramagnetic. For instance, iron has a Curie temperature of about 770°C, and above this temperature, it will no longer be attracted to a magnet.
Physical impact can also lead to demagnetization. Dropping or striking a magnet can disorganize its internal magnetic domains, causing them to become misaligned. This disruption reduces or eliminates the material’s net magnetic field. The more severe the impact, the greater the likelihood of demagnetization.
Exposure to a strong external magnetic field can also affect a magnet’s properties. If a magnet is exposed to an opposing magnetic field of sufficient strength, it can cause the magnetic domains to reorient or become disordered, leading to demagnetization. This principle is utilized in demagnetizers, which often use alternating magnetic fields that gradually decrease in strength to randomize the domain alignment.