“How Magnets Work III”
AS seen earlier on, the most common method of making magnets today involves placing metal in a magnetic field. The field exerts torque on the material, encouraging the domains to align. There’s a slight delay, known as hysteresis, between the application of the field and the change in domains takes a few moments for the domains to start to move. The magnetic domains rotate, allowing them to line up along the north-south lines of the magnetic field. Domains that already pointed in the north-south direction become bigger as the domains around them get smaller. Domain walls, or borders between the neighbouring domains, physically move to accommodate domain growth. In a very strong field, some walls disappear entirely.
The resulting magnet’s strength depends on the amount of force used to move the domains. Its permanence or retentively, depending on how difficult it was to encourage the domains to align. Materials that are hard to magnetize generally retain their magnetism for longer periods, while materials that are easy to magnetize often revert to their original nonmagnetic state easily. You can reduce a magnet’s strength or demagnetize it entirely by exposing it to a magnetic field that is aligned in the opposite direction. You can also demagnetize a material by heating it above its Curie point, or the temperature at which it loses its magnetism. The heat distorts the material and excites the magnetic particles, causing the domains to fall out of alignment.
Let us get to the question as to why Magnets Stick! If you’ve know how Electromagnets Work, you know that an electrical current moving through a wire creates a magnetic field. Moving electrical charges are responsible for the magnetic field in permanent magnets as well. But a magnet’s field doesn’t come from a large current travelling through a wire; it comes from the movement of electrons. Many people imagine electrons as tiny particles that orbit an atom’s nucleus the way planets orbit a sun. As quantum physicists currently explain it, the movement of electrons is a little more complicated than that. Essentially, electrons fill an atom’s shell-like orbital, where they behave as both particles and waves. The electrons have a charge and a mass, as well as a movement that physicists describe as spin in an upward or downward direction.
Generally, electrons fill the atom’s orbital in pairs. If one of the electrons in a pair spins upward, the other spins downward. It’s impossible for both of the electrons in a pair to spin in the same direction. Even though an atom’s electrons don’t move very far, their movement is enough to create a tiny magnetic field. Since paired electrons spin in opposite directions, their magnetic fields cancel one another out. Atoms of ferromagnetic elements, on the other hand, have several unpaired electrons that have the same spin. Iron, for example, has four unpaired electrons with the same spin. Because they have no opposing fields to cancel their effects, these electrons have an orbital magnetic moment. The magnetic moment is a vector; it has a magnitude and a direction. It’s related to both the magnetic field strength and the torque that the field exerts. A whole magnet’s magnetic moments come from the moments of all of its atoms.
In metals like iron, the orbital magnetic moment encourages nearby atoms to align along the same north-south field lines. Iron and other ferromagnetic materials are crystalline. As they cool from a molten state, groups of atoms with parallel orbital spin line up within the crystal structure. This forms the magnetic domains discussed in the previous section. You may have noticed that the materials that make good magnets are the same as the materials magnets attract. This is because magnets attract materials that have unpaired electrons that spin in the same direction. In other words, the quality that turns a metal into a magnet also attracts the metal to magnets. Many other elements are diamagnetic their unpaired atoms create a field that weakly repels a magnet. A few materials don’t react with magnets at all.
(To Be Continued)