Some metals seem to attract other metals more strongly. This force is called magnetism. Even before the discovery of electricity, scientists invented compasses, tiny strips of naturally occurring magnets that rotate to align with the Earth's magnetic field. Since the field moves from south to north, the compass needle always point to the northern magnetic pole. Now we mass-produce magnets and understand how they work.
When two metals are attracted to each other across space, one or both of them are probably magnetic. You may be most familiar with permanent magnets, which are stronger magnets because they have iron in them. This type of magnetism is called ferromagnetism. The Earth's magnetic field is caused by the movements of the molten nickel-iron core of the planet and can be seen when tiny charged particles from the sun collide with Earth's atmosphere close to our planet's magnetic poles, causing them to emit light as they do so. Near the northern magnetic pole, we call the lighting of the magnetic field the northern lights, or aurora borealis.
The atoms that make up the molecules of all matter have a nucleus of neutrons and protons. Orbiting around all of the nuclei are electrons that carry a negative charge. The shape of their orbits gives the atoms a directional orientation, and the orbital motion causes a very weak magnetic field around the atom. Magnetic fields can be caused any time an electrical current is active, but they are strongest when the electrical current is going in a circular or spiral path. Electromagnets use this property, so their magnetism can be turned on and off as the electrical current is turned on and off.
Certain metals have a structure that allows their electrons to more easily line up and form a magnetic field. Iron, nickel, cobalt and gadolinium are the easiest to magnetize. Metals like aluminum and copper can be magnetized also, but the magnetic fields they produce are very weak. Oxides and alloys that have iron in them can also be magnetized easily, such as rust and steel. The more electrons in a metal that can be lined up, the stronger the magnetic field they produce.
Magnetite is an oxide of iron that is frequently discovered in nature with a strong magnetic field. Such samples of magnetite are called lodestones. Modern theories suggest that the magnetite of lodestones was magnetized by lightning strikes. Magnetite can easily have a strong magnetic field because its crystalline structure allows large groups of molecules (called domains) to all have the same polar orientation or direction.
Other minerals can have weak magnetism naturally because of their exposure to the Earth's magnetic field. Studying rocks from the ocean trenches allows us to see how the Earth's magnetic field has flipped (the north and south magnetic poles reversing) over the millennia.
Making a Magnet
All you need to make your own magnet is to wrap lots of coils of copper wiring around a steel bar or nail. Then with a small battery, run a current through the wiring, and the metal will become magnetic (see Resources for instructions). The bar or nail should retain some of its magnetism even after the electrical current has been turned off and the wiring has been removed. Be careful not to touch the exposed metal of the nail or the wiring when the electrical current is on. If the wiring is insulated, you can touch it while the current is active, but you may want to connect a resistor to your circuit, or else the metal can quickly become too hot to touch.