Not just any material can be magnetic. In fact, of all the known elements, only a handful possess magnetic capability and they vary by degree. The strongest magnets are electromagnets, which gain their attractive force only when current passes through them. Current is the movement of electrons, and electrons are what make materials magnetic. There are composite materials that are magnetic, usually referred to as ferrous material, though they are not as strong as electromagnets.
How Magnetism Occurs
In simple terms, magnetism is all about the electrons. Electrons are smaller than microscopic particles that spin around the nucleus of an atom. Each electron behaves like its own tiny magnet with a north and south pole. When an atom's electrons are lined up in the same direction, either all pointing north or all pointing south, the atom becomes magnetic. And because electrons rotate or spin around the nucleus of an atom, it also is possible for an atom to possess a magnetic field when the poles aren't all in alignment due to the electrons' spinning, which makes the atom much like an electromagnet.
No Naturally Magnetic Materials
There are no static elements that are naturally magnetic. There are materials more strongly attracted by magnetic fields. The materials most strongly attracted to a magnetic field are iron and steel. However, there are rare man-made material mixtures that are conducive to becoming electromagnetic by being exposed to a strong magnetic field and holding an electromagnetic charge for long periods of time. Due to their ability to hold a magnetic field for long periods of time, they are considered permanent magnets. The two strongest permanently magnetic materials are iron-neodymium-boron and aluminum-nickel-cobalt.
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How Magnetic Strength Is Measured
The field of magnetics is difficult to explain with precision because there is much that science still doesn't understand about magnetic fields. In simple terms, strong magnetic fields are measured in tesla, and the more common and much weaker magnetic fields found in things like stereo speakers are measured in gauss. It takes 10,000 gauss to make one tesla.
An easier way to describe it is to think about gravitational attraction. The gravity of Earth is considered about 1 tesla or about 10,000 gauss. You can think about the magnetic force of gauss as weight, or the amount of force being exerted by gravitational attraction. It would take 50 feathers to equal 1 gauss of force measured as weight, or in this case, magnetic attraction. Weight and magnetic force are not directly equatable but are offered as an example to give a sense of the magnetic pull or force of a gauss.
Why the Earth Is Magnetic
Scientists know the earth has magnetic property because a free-floating piece of steel or iron will always point to magnetic north. That's where all the lines of longitude converge at the North Pole. While magnetic force can't be exerted on most liquids, it can be imparted on the earth's core, which is comprised of molten iron. And this brings us back to spinning electrons. As the earth spins on its axis, so does its molten iron core and all its electrically charged electrons, which create a magnetic field. The sun also rotates on its axis, and its material as plasma (similar to a liquid consistency) creates its magnetic field.
Like magnetic poles repulse one another while opposite magnetic poles attract. Magnets are naturally drawn to higher magnetic fields. Think of having two magnets, one at 10 tesla and one at 1 tesla. The 10 tesla magnet exerts a stronger magnetic field. A piece of magnetic material, placed equidistant from both magnets, would be attracted to the stronger of the two magnetic fields. So when two magnets of similar polarity approach one another, they appear to push away or be repulsed when in fact they are seeking a higher magnetic field. In other words, two north-oriented magnets seem to be repulsed because they are actually being attracted by the opposite, southern-oriented magnetic field.