Curie point is also used as Curie temperature (Tc) or magnetic transition point.Meansmagnetic material inSpontaneous magnetizationThe temperature when it drops to zero isFerromagnetismorFerromagnetismThe transformation of matter intoParamagnetismThe critical point of matter.The substance becomesFerromagnet, which is related to materialsmagnetic fieldIt's hard to change.When the temperature is higher than the Curie point, the material becomes paramagnetic, and the magnetic field of the magnet is easily changed with the change of the surrounding magnetic field.At this time, the magnetic sensitivity is about 10 to the minus sixth power.Curie point is determined by the chemical composition andcrystal structuredecision.
At the end of the 19th century, a famous physicistPierre Curie （Madame Curie) found in his own laboratory that one of the physical characteristics of a magnet is that when the magnet is heated to a certain temperature, the original magnetism will disappear.Later, people called this temperature“Curie point”。
Explain in detail
Ferromagnetic materialIt has strong magnetism after being magnetized, but with the increase of temperature, the intensification of thermal movement of metal lattice will affectMagnetic domainmagnetic momentWhen the temperature reaches enough to destroy the orderly arrangement of magnetic moments of magnetic domains,Magnetic domainIs disintegrated, the average magnetic moment becomes zero, and the magnetism of ferromagnetic material disappears and becomesParamagnetic material, a series of ferromagnetic properties associated with magnetic domains (such as high permeabilityHysteresis loop、MagnetostrictionAll disappeared, and the corresponding ferromagnetic materialPermeabilityPermeability converted into paramagnetic material.AndFerromagnetismThe temperature corresponding to the disappearance is the Curie point temperature.[1]
Paleomagnetism theory
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On the earth, rocks are subject to the geomagnetic field during diagenesismagnetizationThe magnetic field of the magnetized rockgeomagnetic fieldIs consistent.That is to say, no matter how the geomagnetic field changes direction, as long as its temperature is not higher than the Curie point, the magnetism of rocks will not change.According to this reason, as long as the magnetism of rocks is measured, the current geomagnetic direction can be inferred naturally.This is whereGeoscienceFossil magnetism is often referred to in research.On this basis, scientists use the principle of fossil magnetism to study the evolution history of the earthgeomagnetic fieldThe law of change isPaleomagnetism theory。[2]
To findContinental drift theoryScientists have introduced paleomagnetism into the field of marine geology and achieved encouraging results.
the Second World WarLater, scientists used a highly sensitive magnetic detector toMid Atlantic RidgeThe paleomagnetic survey was carried out on the sea surface above.Later, people used magnetometers and other instruments to conduct paleontology in the Pacific Ocean in the form of dense survey linesGeomagnetic survey。The data from the two surveys surprised people to find that there is an equimagnetic line belt at the bottom of the ocean, which is parallel to both sides of the central axis of the Great Ocean Ridge in north-south direction, with positive and negative magnetism alternating.Each magnetic line belt is about hundreds of kilometers long, and its width varies from tens of kilometers to hundreds of kilometers.The discovery of magnetic stripes on the seabed has become a miracle of geoscience research in this century.In 1963,University of CambridgeF., a young scholar ofJ. Vain and his teacher DH. Matthews proposed that if“Seafloor spreading”It happened, so,Mid ocean ridgeUpwelling lava should be preserved when it solidifiesGeomagnetic fieldMagnetization direction.That is to say, there should be magnetic bands with the same magnetization on the seafloor on both sides of the ridge.When the earth's magnetic field reversesPolarityReversal should also occur, and the width of the magnetic strip can be used as a measure of the time between two reversals.This bold hypothesis was quickly confirmed, and people found the same symmetrical magnetic bands in the Pacific Ocean, the Atlantic Ocean and the Indian Ocean.Moreover, scientists have calculated that 171 reversals have occurred on the earth in 76 million years.
Research findings
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The study also found that the longest period between the two reversals of the earth's magnetic field is about 3 million years, the shortest period is about 50000 years, and the average period of the two reversals is about 42-480000 years.The direction of the earth's magnetic field has been retained for 700000 years, so people feel that a new magnetic field change may be approaching us.
The research on submarine magnetic stripe is still in progress, and many problems cannot be solved satisfactorily.For example, the basic question of why the earth's magnetic field reverses back and forth cannot be explained clearly.Although scientists have put forward various hypotheses, the real reason is still unclear.In other words, the mystery of the internal law of the earth's magnetic field turning needs to be further explored by scientists.
Related impacts
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Once the core temperature exceeds its Curie temperature, its permeability will drop sharply (according tomagnetic material The broad definition of the manufacturer has begun to decline sharply before reaching the defined Curie temperature).That is to say, after reaching the Curie temperature, the electromagnetic effect of the magnetic core can no longer work, and the consequences are very serious.
Magnetic cores of different materialsCurie temperatureNot fixed.For manganese and zinc, it is common to consider the Curie temperature effect (the Curie temperature of other materials is higher). The Curie temperature of power materials is below 230 ℃, and that of high conductivity materials is below 120 ℃.If the high conductivity magnetic core is used, and the transformer has high temperature resistance requirements, it must be considered.
If the Curie temperature is exceeded, ferromagnetism will change into paramagnetism, which should not involve phase distortion, because some volumes will expand and contract, causing density changes, and the quality should not change, unless too much is volatilized beyond the temperature.
As for each type of Tcmagnetic material Are different, such asironThe Curie temperature of is about 770 ℃,cobaltThe Curie temperature of is about 1131 ℃.
Not at any temperature,magnetic material Are magnetic.The magnetic material has acritical temperatureTc，That is, the Curie temperature. Above this temperature, due to the intense thermal movement of atoms at high temperature, the arrangement of atomic magnetic moments is disordered, and the magnetization of ferromagnetic materials decreases with the increase of temperature. It determines the upper limit temperature for the operation of magnetic devicesInductanceIt will decrease until it disappears, and the circuit cannot work normally.[3]
Generally, the Curie temperature of PC40 and PC44 is 210 ℃.
Select the appropriate magnetic core according to the circuit needs and working conditions.
Usually, small and medium power switching power supplytransformerThe magnetic core is usually made of the core material near 200 ℃.
Using this feature, many control elements have been developed.For example, the rice cooker we use takes advantage of the Curie point of magnetic materials.A magnet and a magnetic material with a Curie point of 103 ℃ are installed at the bottom center of the rice cooker.When the water in the pot is dry, the food temperature will rise from 100 ℃.When the temperature reaches about 103 ℃, because the magnetism of the magnetic material absorbed by the magnet disappears, the magnet loses its attraction to it. At this time, the spring between the magnet and the magnetic material will separate them and drive the power switch to be disconnected to stop heating.
