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Magnet manufacturers tell you why magnets can attract iron but not wood and aluminum?

We must have played with magnets when we were young, and we must have discovered such a phenomenon: magnets can attract iron products such as nails and iron sheets, but they cannot attract wooden tables or aluminum pots. To understand the magnetism in solids, we must first understand the quantum property of electrons-spin. Just like charge and mass, spin is also an intrinsic property of microscopic particles. It is not caused by the rotation of microscopic particles, but an inevitable characteristic of quantization. The spin of the electron will produce a spin magnetic moment, and the movement of the electron around the nucleus will also produce an orbital magnetic moment, the direction of the magnetic moment is perpendicular to the plane of the loop, and the magnetic moment can be regarded as a small magnetic needle. If there is


Everyone must have played with magnets when they were young, and they must have discovered such a phenomenon: magnets can attract iron products such as nails and iron sheets, but they cannot attract wooden tables or aluminum pots. Why is this?

To understand magnetism in solids, one must first understand the quantum property of electrons-spin. Just like charge and mass, spin is also an intrinsic property of microscopic particles. It is not caused by the rotation of microscopic particles, but an inevitable characteristic of quantization. The spin of the electron will produce a spin magnetic moment, and the movement of the electron around the nucleus will also produce an orbital magnetic moment, the direction of the magnetic moment is perpendicular to the plane of the loop, and the magnetic moment can be regarded as a small magnetic needle. If the ordered atomic magnetic moments are the same size and the same direction, then the material as a whole will be magnetic.

solenoid magnetic field

Experiments show that any substance is more or less magnetized in an external magnetic field, but the degree of magnetization is different. Iron is a ferromagnetic material. There is a certain interaction (restriction) between the magnetic moments of adjacent atoms or ions in ferromagnetic materials, which will make the magnetic moments in some areas roughly arranged in the same direction, thus forming a magnetic domain, and the magnetism in the magnetic domain is very strong. There are many such domains in the material, but the magnetic moment orientation of different domains is random, and the material as a whole does not exhibit strong magnetism. The main reason for the magnet to attract iron is that the iron itself has undergone spontaneous magnetization, and the formation of a spontaneous magnetization region is the magnetic domain. After the ferromagnetic substance is magnetized, the internal magnetic domains will be arranged neatly to make the whole show magnetism, so that it can be attracted by the magnet. In addition to iron, cobalt, nickel, gadolinium, neodymium and other transition metals and rare earth metals have spontaneous magnetization properties. After the magnet is removed, some ferromagnetic materials can still maintain the orderly arrangement of magnetic domains and retain magnetism, while others will quickly disappear magnetism. The magnetic properties of pure iron are not easy to maintain, and the magnetic properties of steel cast with a certain amount of carbon and other impurities are very good. At present, the strongest permanent magnet is neodymium iron boron material, which is called "magnet king" because of its excellent magnetic properties, and has important applications in modern industry and electronic technology.

There is no magnetic domain inside the wood, and the electronic magnetic moments in its atoms cancel each other out. When subjected to an external magnetic field, it will produce a tiny magnetic moment that resists the external magnetic field, resulting in being unable to be attracted. Aluminum is a paramagnetic substance. When it is not affected by a magnetic field, the magnetic moment is arranged in disorder. After adding an external magnetic field, the magnetic moment tends to be consistent with the external magnetic field, but the consistency is not as strong as that of ferromagnetic materials, so ordinary magnets cannot attract aluminum blocks.

The magnetic properties of solid materials are also related to the temperature of the material. For ferromagnetic materials, above a certain temperature, the thermal vibration of atoms is too severe and disrupts the original consistent arrangement of magnetic moments, the material will transition from ferromagnet to paramagnetic, the corresponding temperature point is called the Curie point. The Curie point of the ferromagnet is used in the domestic electric rice cooker. When the rice in the cooker is heated to around 103 ℃, the Curie point of the ferromagnetic material under the electric rice cooker is reached. The attraction force of the demagnetized magnetic steel sheet is greatly reduced, thus automatically turning off the heating switch and allowing the electric rice cooker to enter the heat preservation state, so that the rice can be cooked without being burnt.

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Source: magnet manufacturers Youlian Magnetic Industrywww.youliancy.com

 

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