Development of magnets

The development history of magnets is as follows:

Humans discovered natural magnets (Fe3O4) 5000 years ago

2300 years ago, the Chinese grind natural magnets into a spoon shape and place them on a smooth surface. Under the influence of geomagnetism, the spoon handle guides, called "Sinan", which is the guide instrument.

1000 years ago, the Chinese used magnets and iron needles to friction magnetize to make an earlier compass.

Around 1100, China integrated the magnet needle and the azimuth plate into a magnet-type compass, which was used for navigation.

1405-1432 Zheng He started the great pioneering work of navigation in the history of mankind with the guide.

1488-1521 Columbus, Gamma, Magellan used a compass to make a voyage discovery.

In 1600, the Englishman William Gilber published the monograph "Magnet" on magnetism, which developed the knowledge and experiments of the ancient Greeks Thales, Aristotle and other predecessors on magnetism.

In 1785, French physicist C. Coulomb used torsion to establish the "Coulomb's law" that describes the force between electric charges and magnetic poles.

1820 Danish physicist H.C. Oersted discovered that electric current induces magnetic force.

1831 British physicist M. Faraday discovered the phenomenon of electromagnetic induction.

1873 British physicist J.C. Maxwell completed a unified electromagnetic theory in his monograph "On Electricity and Magnetism".

1898-1899 French physicist P. Curie discovered that ferromagnetic materials become paramagnetic at a certain temperature (Curie temperature).

1905 French physicist P.I. Langevin explained the change of paramagnetism with temperature based on the theory of statistical mechanics.

1907 French physicist P.E. Weiss proposed the molecular field theory, which extended Langevin's theory.

1921 Austrian physicist W. Pauli proposed the Bohr magneton as the basic unit of atomic magnetic moment. American physicist A. Compton proposed that electrons also have a magnetic moment corresponding to spin.

1928 British physicist P.A.M. Dirac used relativistic quantum mechanics to explain the intrinsic spin and magnetic moment of electrons. Together with the German physicist W. Heisenberg, he proved the existence of the exchange force derived from static electricity, laying the foundation of modern magnetism.

1936 Soviet physicist Lang Dao completed the masterpiece "Theoretical Physics Course", which contains a comprehensive and wonderful chapter on modern electromagnetism and ferromagnetism.

1936-1948 French physicist L. Nair proposed the concepts and theories of antiferromagnetism and ferrimagnetism, and deepened his understanding of material magnetism in the subsequent years of research.

In 1967, under the guidance of quantum magnetism, the Austrian physicist K.J. Snitter discovered an unprecedentedly high magnetic energy product.

Rare earth magnet (SmCo5), thus opening a new chapter in the development of permanent magnet materials.

In 1967, Strnat and others of Dayton University in the United States developed samarium-cobalt magnets, marking the arrival of the era of rare earth magnets.

1974 The second generation rare earth permanent magnet-Sm2Co17 came out.

1982 Masato Sagawa of Sumitomo Special Metals invented neodymium iron boron magnets, and the third generation of rare earth permanent magnets -Nd2Fe14B came out.

1990 Atomic interstitial magnet -Sm-Fe-N came out.

In 1991, the German physicist E.F. Kneller proposed the theoretical basis for the exchange of two-phase composite magnets and pointed out the development prospects of nanocrystalline magnets.

With the development of society, the application of magnets has become more and more extensive. From high-tech products to simpler packaging magnets, neodymium iron boron magnets and ferrite magnets are currently more widely used.

From the perspective of the development history of magnets, at the end of the 19th century and the beginning of the 20th century, people mainly used carbon steel, tungsten steel, chromium steel and cobalt steel as permanent magnet materials.

Thirties

At the end of the 1930s, the successful development of AlNiCo magnets made the large-scale application of magnets possible.

Fifties

In the 1950s, the appearance of barium ferrite magnets not only reduced the cost of permanent magnets, but also expanded the application range of permanent magnet materials to the high-frequency field.

Sixties

In the 1960s, the emergence of samarium-cobalt permanent magnets opened up a new era for the application of magnets. So far, rare earth permanent magnets have experienced the first generation of SmCo5, the second generation of precipitation hardening Sm2Co17, and the third generation of Nd-Fe-B permanent magnet materials. At present, ferrite magnets are still a relatively large amount of permanent magnet materials, but the output value of neodymium iron boron magnets has greatly exceeded that of ferrite permanent magnet materials, and the production of neodymium iron boron magnets has developed into a major industry.

The discovery of magnetic phenomena

During the Warring States period, our ancestors have accumulated a lot of knowledge in this area. When exploring iron ore, they often encounter magnetite, that is, magnet (the main component is ferroferric oxide). These discoveries were recorded very early. Several articles in "Guan Zi" recorded these findings early: "If there is a magnet on the mountain, there is gold and copper under it."

Documentation

Other ancient books such as "Shan Hai Jing" also have similar records. The iron-attracting properties of magnets were discovered very early. The nine-volume masterpiece of "Lü Shi Chunqiu" contains: "Compassion recruits iron, or it can be introduced." At that time, people called "magnetism" as "kindness" and they attracted magnets. Tie sees the attraction of loving mothers to their children. He thinks: "Stone is the mother of iron, but there are two kinds of stone, kind and unkind. A kind stone can attract his children, and an unkind stone can't." Before the Han Dynasty, people wrote magnets as "kind stone." The meaning of loving-kind stone.

Three hundred and twenty miles to the north, it is called the mountain of Guanti, with many barnyards above it, and quicksand and piles below it. There is a beast yan, which looks like a cow with a white tail, and its sound is like a gu, and its name is the father. There is a bird yan, which looks like a female pheasant with a human face, and leaps when he sees a person. The craftsman Han Zhishui flows out of Yan, and the west flows into Lize, where there are many magnets.

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③Magnetite: also known as "mite stone", a natural ore that has the property of attracting metal substances such as iron, nickel, and cobalt. Commonly known as magnetite, now called magnetite. The compass, one of the four great inventions of ancient China, is made of magnets.

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