Magnetism is a fundamental force of nature that causes attraction or repulsion between objects. This force originates from the motion of electric charges, such as electrons within atoms or an electric current. The region around a magnet where its influence can be detected is known as a magnetic field. This article explores materials that exhibit magnetic properties and how they can be used or created as magnets.
Materials That Become Magnetic
Materials interact with magnetic fields in different ways, leading to their classification into several categories.
Ferromagnetic materials are strongly attracted to magnetic fields and can retain their magnetic properties after the external field is removed. Common examples include iron, nickel, and cobalt, along with their alloys. Their strong magnetic properties stem from microscopic regions called magnetic domains, where the magnetic moments of many atoms are aligned. In an unmagnetized material, these domains are randomly oriented, canceling out each other’s magnetic effects. When exposed to an external magnetic field, these domains align with the field, leading to a strong magnetic response and allowing them to become permanent magnets.
Paramagnetic materials are weakly attracted to magnetic fields but do not retain their magnetism once the external field is removed. This weak attraction occurs because they have some unpaired electrons whose spins align slightly with the external field. Examples include aluminum, oxygen, and platinum.
Diamagnetic materials, in contrast, are weakly repelled by magnetic fields. This repulsion happens because all their electrons are paired, meaning there is no net magnetic moment per atom. Common substances like copper, water, and gold are diamagnetic.
Different Kinds of Magnets
Magnets can be categorized based on how they retain their magnetic properties and how their magnetic fields are generated.
Permanent magnets produce their own persistent magnetic field and retain magnetism without external influence. This lasting magnetic field is created by the alignment of electron spins within materials like iron, cobalt, and nickel. These magnets are commonly found on refrigerators or used in compasses.
Temporary magnets only exhibit magnetic properties when in the presence of a strong external magnetic field or an electric current. A common example is a paper clip that temporarily becomes magnetic when touched by a strong permanent magnet, losing its magnetism when separated.
Electromagnets are created by passing an electric current through a coil of wire, often wrapped around a ferromagnetic core like iron. Their strength can be controlled by adjusting the current, and they can be turned on or off by completing or interrupting the electrical circuit. This makes them useful in applications such as scrapyard cranes and various electric motors.
How to Create a Magnet
Materials that can become magnetic, particularly ferromagnetic ones, can be magnetized through several practical methods.
One common technique is the stroking method, where a ferromagnetic material, such as an iron nail, is repeatedly rubbed in one direction with a permanent magnet. Each stroke helps to align the magnetic domains within the material, gradually turning it into a temporary magnet. It is important to lift the stroking magnet away after each pass to maintain the alignment.
Another method is magnetic induction, which occurs when a magnetic material is placed near or in direct contact with a strong magnet. The strong magnetic field causes the domains within the material to align, inducing temporary magnetism. For instance, if an iron nail touches a permanent magnet, it becomes a temporary magnet capable of attracting other small magnetic objects. This induced magnetism disappears once the strong magnet is removed.
The electrical method creates electromagnets, offering a controllable way to produce magnetism. This involves coiling an insulated wire, often copper, around a core, frequently made of a ferromagnetic material like iron. When an electric current passes through the coil, a magnetic field is generated. The strength of this electromagnet can be increased by using more turns of wire or by increasing the current.