How were magnetic materials discovered?

The ancient Greeks and China discovered that there was a naturally magnetized stone in nature, called a "magnet". Magnets are not invented by humans, but there are natural magnetite. It was probably China who first discovered and used magnets. One of the four great inventions, Sina, is the magnet. Magnets are composed of iron, cobalt, nickel, etc. Their atomic structure is special, and the atom itself has a magnetic moment. Generally, the molecules of these minerals are arranged in disorder, and the interaction of magnetic regions will not show magnetism. However, under the guidance of external forces (such as magnetic fields), the molecular arrangement tends to be consistent, showing magnetism, which is also commonly known as magnets. Iron, cobalt and nickel are the most commonly used magnetic substances. During the Warring States period, a natural magnet was placed on a graduated copper plate for divination.

In the Northern Song Dynasty, artificial magnets were made in two ways. One is to place the red-hot iron needle in the north-south direction, and after rapid cooling, the iron needle is magnetized by the earth's magnetic field. The other is made by rubbing an iron needle with a magnet. Magnet is just a general term, which refers to something with magnetism. The actual composition does not necessarily contain iron. Because the magnetic principle of magnets is explained as follows: there are many tiny current loops in a general object (for example, electrons move around to form current loops), and these current loops will produce corresponding magnetic effects. Because the direction of the magnetic field generated by the current loop inside the general object is chaotic, and the magnetic fields in all directions cancel each other, the object is non-magnetic macroscopically; From this, it can be considered that the magnetism of magnets is due to the arrangement of some tiny circuits inside the object for some reason (such as putting nonmagnetic iron blocks in a constant magnetic field for a long time), and the total magnetic field intensity in one direction is greater than that in other directions, thus showing magnetism.