Magnetic materiels

Magnets are really common in our lives. They have many  applications such as compass, electric motor, and refrigerator magnets. In addition, they are used to lift heavy metals sometimes. Magnets really bring convenience to our lives. Today, I am going to talk about how do magnets formed and the theory behind them.

First, we have to understand that only the specific material can become permanent magnets. Theses materials are: iron, nickle, cobalt, and some rare earth metals. Those materials are attracted easily by magnetic fields. You may wander what's special about these materials. To understand why those materials respond to magnetic fields, we have to move to the scale of atoms. We all know that every materials are formed by individual atoms. In those atoms, there are some electrons which have different direction of spin(clockwise or counter clockwise). The spin of electron forms magnetic dipole moments of electron. If the spin of an electron is clockwise, this electron has a magnetic dipole moment which points upward. If the spin is counter clockwise, the electron has magnetic dipole moments that points downward. Two magnetic dipole moments which point to opposite directions will cancel each other and have a 0 total dipole moment. In many materials, the electrons in atoms are paired. Those paired electrons are two electrons which have opposite direction of spin, forming a 0 dipole moment. (you can refer dipole moment to a tiny magnet) However, in some materials, the electrons are not totally paired so the magnetic dipole moments are non-zero in the atoms. In the normal condition, there are lots of magnetic dipole moments point to different directions in those materials. The arrangement of dipole moments are random, cancelling each other and have 0 dipole moment in the whole material. This property is called ferromagnetic. If there's a magnets applied, however, the dipole moments in those materials will point to the same direction and became magnetized. Moreover, if this kind of materials' temperature increase to a specific point, the dipole moments on these materials will also point to the same direction.

To form a permanent magnets, one must find ferromagnetic materials and apply a magnetic fields to them. Then the ferromagnetic of these materials will disappear and become paramagnetic(a state when magnetic dipole moment of a material point to same direction). If the magnetic field is strong enough, and influences the material for a period of time, this material will stay in paramagnetic state, holding magnetism even when the magnetic field is removed.

I hope you enjoy this article and understand how the permanent magnets formed and the properties of magnetic materials.