HiSET Science: Properties of Magnets

Magnets and Magnetism
A magnet is a piece of metal, such as iron, steel, or magnetite (lodestone) that can affect another substance within its field of force that has like characteristics. Magnets can either attract or repel other substances. Magnets have two poles: north and south. Like poles repel and opposite poles (pairs of north and south) attract. The magnetic field is a set of invisible lines representing the paths of attraction and repulsion.
Magnetism can occur naturally, or ferromagnetic materials can be magnetized. Certain matter that is magnetized can retain its magnetic properties indefinitely and become a permanent magnet. Other matter can lose its magnetic properties. For example, an iron nail can be temporarily magnetized by stroking it repeatedly in the same direction using one pole of another magnet. Once magnetized, it can attract or repel other magnetically inclined materials, such as paper clips. Dropping the nail repeatedly will cause it to lose its magnetic properties.

Magnetic Fields and Atomic Structure
The motions of subatomic structures (nuclei and electrons) produce a magnetic field. It is the direction of the spin and orbit that indicate the direction of the field. The strength of a magnetic field is known as the magnetic moment. As electrons spin and orbit a nucleus, they produce a magnetic field.
Pairs of electrons that spin and orbit in opposite directions cancel each other out, creating a net magnetic field of zero.
Materials that have an unpaired electron are magnetic. Those with a weak attractive force are referred to as paramagnetic materials, while ferromagnetic materials have a strong attractive force. A diamagnetic material has electrons that are paired, and therefore does not typically have a magnetic moment. There are, however, some diamagnetic materials that have a weak
A magnetic field can be formed not only by a magnetic material, but also by electric current flowing through a wire. When a coiled wire is attached to the two ends of a battery, for example, an electromagnet can be formed by inserting a ferromagnetic material such as an iron bar within the coil. When electric current flows through the wire, the bar becomes a magnet. If there is no current, the magnetism is lost. A magnetic domain occurs when the magnetic fields of atoms are grouped and aligned. These groups form what can be thought of as miniature magnets within a material. This is what happens when an object like an iron nail is temporarily magnetized. Prior to magnetization, the organization of atoms and their various polarities are somewhat random with respect to where the north and south poles are pointing. After magnetization, a significant percentage of the poles are lined up in one direction, which is what causes the magnetic force exerted by the material.