2. Permanent magnets can be natural products, also known as natural magnets, or artificial (the strongest magnet is neodymium magnet).
3. When a non-permanent magnet is heated to a certain temperature, it will suddenly lose its magnetism, which is caused by the arrangement of many "meta-magnets" that make up the magnet from order to disorder; Put the lost magnet into the magnetic field. When the magnetization reaches a certain value, it is magnetized again, and the arrangement of "super magnets" changes from disorder to order.
The ancient Greeks and China discovered that there was a naturally magnetized stone in nature, which was called "magnet". This kind of stone can magically pick up a small piece of iron and swing it at will and always point in the same direction. Early navigators used this magnet as their earliest compass to tell directions at sea.
After thousands of years of development, magnets have become a powerful material in our life today. By synthesizing alloys of different materials, we can achieve the same effect as magnets and improve the magnetic force. /kloc-artificial magnets appeared in the 0/8th century, but the process of making stronger magnetic materials was very slow, and Al-Ni-Co was not produced until the 1920s. Subsequently, ferrite was manufactured in 1950s and [rare earth magnets [including NdFeB and SmCo]] was manufactured in 1970s. At this point, magnetic science and technology developed rapidly.