The material that can react to the magnetic field in some way is called magnetic material.According to the strength of the magnetism of substances in the external magnetic field, they can be divided into diamagnetic substances, paramagnetic substances, ferromagnetic substances, antiferromagnetic substances and ferromagnetic substances.Most materials are diamagnetic or paramagnetic, and their response to external magnetic field is weak.Ferromagnetic materials and ferromagnetic materials are strong magnetic materials, and the commonly said magnetic materials refer to strong magnetic materials.For magnetic materials, magnetization curve and hysteresis loop are characteristic curves reflecting their basic magnetic properties.Ferromagnetic materials are generally Fe, Co, Ni elements and their alloys, rare earth elements and their alloys, and some Mn compounds.Magnetic materials are generally divided intoSoft magnetic materialandHard magnetic material。
according toMolecular current hypothesisThe material should show similar characteristics in the magnetic field, but it tells us that the characteristics of the material in the external magnetic field are very different.This reflectsMolecular currentLimitations of the hypothesis.In fact, the microstructure of various substances is different, and this difference in material structure is the reason for the difference in material magnetism.
We call paramagnetic and diamagnetic materialsWeakly magnetic material, ferromagnetic materials are calledStrong magnetic material。
Generally speaking, magnetic materials refer to strong magnetic materials.Magnetic materials can be divided intoSoft magnetic materialsandHard magnetic material。The material that is easy to remove magnetism after magnetization is called soft magnetic material, and the material that is not easy to remove magnetism is called hard magnetic material.Generally speaking, the remanence of soft magnetic materials is small, while that of hard magnetic materials is large.[1]
Magnetic materials are composed of ferromagnetic materials or ferromagnetic materials. Under the action of external magnetic field H, there must be corresponding magnetization M orMagnetic inductionB，They followmagnetic field intensityThe change curve of H is called magnetization curve (M-H or B-H curve).The magnetization curve is generally nonlinear and has two characteristics: magnetic saturation and hysteresis.That is, when the magnetic field strength H is large enough, the magnetization M reaches a certain saturation value Ms, and continues to increase H, Ms remains unchanged;And when the M value of the material reaches saturation and the external magnetic field H decreases to zero, M does not return to zero, but changes along the MsMr curve.The working state of the material is equivalent to a point on the M ～ H curve or B ～ H curve, which is often called the working point.
Saturated magnetic inductionBs: its size depends on the composition of the material, and its corresponding physical state is the orderly arrangement of magnetization vectors inside the material.
surplusMagnetic inductionBr: is the characteristic parameter on the hysteresis loop, and the B value when H returns to 0.
Rectangle ratio: Br ／ Bs
CoercivityHc: the quantity indicating the difficulty of magnetization of the material, which depends on the composition and defects of the material (impuritiesstressEtc.).
Permeabilityμ: Is the ratio of B to H corresponding to any point on the hysteresis loop, anddeviceThe working status is closely related.
Initial permeability μ i, maximum permeability μ m, differential permeability μ d, amplitude permeability μ a, effective permeability μ epulsePermeability μ p.
Curie temperatureTc: The magnetization of ferromagnetic material decreases with the increase of temperature. When it reaches a certain temperature, the spontaneous magnetization disappears and turns into paramagnetism. The critical temperature is the Curie temperature.It determines the upper limit temperature of magnetic device operation.
Loss P:Hysteresis lossPh andEddy current lossPe P=Ph+Pe=af+bf2+c Pe ∝ f2 t2/, ρ decreases. The method to reduce the hysteresis loss Ph is to reduce the coercive force Hc;The method to reduce eddy current loss Pe is to reduce the thickness t of magnetic materials and improve theresistivityρ。Loss of magnetic core in free static air andtemperature riseThe relationship is: total powerdissipation(mW)/surface area (cm2)
3. Soft magnetic materialMagnetic parametersDevice relatedElectrical parametersConversion between
When designing soft magnetic devices, the voltage current characteristics of the devices should be determined according to the requirements of the circuit.The voltage current characteristics of the device are closely related to the geometric shape and magnetization state of the magnetic core.The designer must be familiar with the magnetization process of materials and master the conversion relationship between the magnetic parameters of materials and the electrical parameters of devices.The design of soft magnetic devices usually includes three steps: correct selection of magnetic materials;Reasonably determine the geometric shape and size of the magnetic core;According to the magnetic parameter requirements, the corresponding electrical parameters are obtained by simulating the working state of the magnetic core.
brief history
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Hysteresis Loop of Magnetic Materials
China is the first country in the world to discover the phenomenon of material magnetism and apply magnetic materials.Natural magnetic materials (such asmagnetite）Records.The method of manufacturing artificial permanent magnetic materials was invented in the 11th century.1086《Mengxi Writing》It records the making and use of the compass.From 1099 to 1102, the compass was used for the record of navigation. At the same timeGeomagnetic declinationPhenomenon.In modern times, the development of electric power industry has promoted the development of metal magnetic materialsSilicon steel sheets(Si Fe alloy).Permanent magnet metalcarbon steelRare earth developed laterPermanent magnet alloy, the performance has been improved more than 200 times.With the development of communication technology, soft magnetic metal materials are still unable to meet the requirements of frequency expansion from sheet to wire and then to powder.In the 1940s, J50. Snoik Invents Ferrite with High Resistivity and High Frequency CharacteristicsSoft magnetic materialThen came the cheapPermanent ferrite。In the early 1950s, with the development of electronic computers, Chinese AmericansWang AnFirst use moment magnetic alloyelementAs a computer's internal memory, it was soonRectangular ferriteMemory magnetic core replaced, which played an important role in the development of computers in the 1960s and 1970s.In the early 1950s, it was found that ferrite had unique microwave characteristics and was made into a series ofMicrowave ferrite device。Piezomagnetic materialsthe First World WarIt has been used in sonar technology sincePiezoelectric ceramicsThe use of is reduced.Then came the strong pressure magneticRare earth alloy。Amorphous state(Amorphous) magnetic materials are the achievements of modern magnetic research. After the invention of rapid quenching technology, the tape making process was solved in 1967, and the transition to practical use was positive.
On February 19, 2024, South University of Science and Technology reported that Associate Professor Liu Chang and Professor Liu Qihang of the Department of Physics of the University cooperated with Qiao Shan, a researcher of Shanghai Institute of Microsystems and Information Technology, Chinese Academy of Sciences, and found a new type of magnetic material - unconventional antiferromagnet through experiments.The magnet is expected to become an ideal next generation spintronic material for high-density magnetic memory devices and other fields.Relevant research results were published in Nature[3]。
classification
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Magnetic materials have strong magnetic materials with magnetic order, and generally include weak magnetic and antiferromagnetic materials that can apply their magnetism and magnetic effects.Magnetism is a basic property of matter.Materials can be divided into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferromagnetic materials according to their internal structure and properties in the external magnetic field.Ferromagnetic and ferromagnetic materials are strong magnetic materials, diamagneticHarmonyMagnetic substances are weakly magnetic substances.Magnetic materials can be divided into metal and nonmetal according to their properties. The former mainly includes electrical steelNickel base alloyAnd rare earth alloys, the latter mainly includesFerrite material。According to the use, it can be divided into soft magnetic materials, permanent magnetic materials and functional magnetic materials.Functional magnetic materials mainly includeMagnetostrictive material、Magnetic recording material、Magnetoresistance material、Magnetic bubble material、Magneto-optical material, gyromagnetic materials andMagnetic film materialThe magnetization curve, hysteresis loop andMagnetic lossEtc.
Permanent magnetic material
magnetic material
After being magnetized by the external magnetic field, even under the action of a relatively large reverse magnetic field, the magnetism in one or most of the original magnetization direction can still be maintained.The requirement for such materials is the residual magnetic induction strengthBR high, coercivity BHC (i.e. anti demagnetization ability) is strong, and the magnetic energy product（BH）(that is, theMagnetic field energy）Large.Compared with soft magnetic materials, it is also calledHard magnetic material。Permanent magnetic materials include alloyFerriteandIntermetallic compoundClass III. ①Alloys: including casting, sintering and machinable alloys.Casting alloyThe main varieties are: AlNi (Co), FeCr (Co), FeCrMo, FeAlC, FeCo (V) (W);Sintered alloys include: Re Co (Re represents rare earth element), Re Fe, AlNi (Co), FeCrCo, etc;Machinable alloys include FeCrCo, PtCo, MnAlC, CuNiFe and AlMnAg, among which BHC The lower one is also called semi permanent magnetic material. ②Ferrites: the main component is MO · 6Fe2O3, and M represents Ba, Sr, Pb or SrCa, LaCa and other composite components. ③Intermetallic compounds: mainly represented by MnBi.
Permanent magnetic materials have many uses. ①be based onElectromagnetic forceThe application of action principle mainly includes: speaker, microphone, electricity meter, button, motorrelay、sensor, switches, etc. ②Applications based on the principle of magnetoelectric action mainly include:MagnetronandTraveling wave tubeetc.Microwave tube、Kinescope, titanium pumpMicrowave ferrite device, magnetoresistive deviceshall element Etc. ③be based onmagnetic forceThe application of action principle mainly includes:Magnetic bearing, concentratorMagnetic separatorMagnetic chuck, magnetic seal, magnetic blackboard, toy, nameplate, password lock, photocopier, temperature controller, etc.Other applications include: magnetic therapy, magnetized water, magnetic anesthesia, etc.
Permanent magnetic materials can have different structures and shapes according to the needs of use.Some materials are also isotropic andanisotropyDifference.
Soft magnetic material
Its function is mainly to transform and transmit magnetic conductivity and electromagnetic energy.Therefore, high permeability andMagnetic inductionAt the same time, the area or magnetic loss of hysteresis loop is small.In contrast to permanent magnet materials, the smaller the Br and BHC, the better, but the larger the saturation magnetic induction Bs, the better.
Soft magnetic materials can generally be divided into four categories. ①Alloy strip or sheet: FeNi (Mo), FeSi, FeAl, etc. ②Amorphous alloyThin tape: Fe based, Co based, FeNi based or FeNiCo based, with appropriate Si, B, P and other doped elements, also known as magnetic glass. ③Magnetic medium(Iron core): FeNi (Mo), FeSiAlcarbonylPowders such as iron and ferrite are pressed and formed as required after being coated and bonded with electrical insulating medium. ④Ferrite: includingspinelType - M O · Fe2O3 (M represents NiZn, MnZn, MgZn, Li1/2Fe1/2Zn, CaZn, etc.); type of magnetic lead stone - Ba3Me2Fe24O41 (Me represents Co, Ni, Mg, Zn, Cu and their composite components).Soft magnetic materials are widely used, mainly for magnetic antennasInductor, transformer, magnetic head, earphone, relay, vibrator, TV yoke, cable, delay line, sensorMicrowave absorbing material、electromagnet、acceleratorHigh frequency accelerating cavity, magnetic field probe, magnetic substrate, magnetic field shielding, high frequency quenching and energy gatheringElectromagnetic chuckMagnetic sensors (such as magnetothermal materials as switches).
It is mainly used for information recording, contactless switch, logic operation and information amplification.This material is characterized by a rectangular hysteresis loop.
Gyromagnetic material
It has unique microwave magnetism, such as the tensor property of permeabilityFaradThe first rotationResonance absorption, field shift, phase shift, dualrefractionandspinWave effect.The devices designed on this basis are mainly used for the transmission and conversion of microwave energyisolator , circulatorwave filteringDevices (fixed or electrically modulated), attenuators, phase shifters, modulators, switches, limiters, delay lines, etc., as well as still developing magnetic surface wave and magnetostatic wave devices (seeMicrowave ferrite device）。Commonly used materials have formed series, including Ni system, Mg system, Li system, YlG system and BiCaV systemFerrite material；It can be made into single crystal, polycrystalline, amorphous or thin film structures and shapes according to the needs of devices.
Piezomagnetic material
This kind of material is characterized by mechanical deformation under the action of external magnetic field, so it is also calledMagnetostrictive materialIts function is to convert magnetic sound or magnetic energy.Commonly used forThe ultrasonic generatorVibrating head ofMechanical filterAnd electrical pulse signal delay line, etc., can be combined with microwave technology to produce micro acoustic (or gyroscopic) devices.Due to the high mechanical strength of alloy materials, vibration resistance without cracking, the vibrating head is mostly made of Ni series and NiCo series alloys;Ni series and NiCo series ferrites are mostly used under small signal.Amorphous alloyThe new type with stronger piezomagnetism is suitable for making delay lines.The production and application of piezomagnetic materials are far less than the previous four materials.
Application of magnetic materials transformer
Magnetic materials are used in production, lifeNational defense science and technologyMaterials widely used in.Such as manufacturing various motors and transformers in electric power technology, and various types in electronic technologyMagnetic elementandMicrowave tube, filters and amplifiers in communication technology,Defense technologyInMagnetic mineElectromagnetic gun, various household appliances, etc.In addition, magnetic materials have also been widely used in geological and mineral exploration, ocean exploration, and new technologies of information, energy, biology and space.Magnetic materials are widely used.It is mainly to use its various magnetic properties and special effects to make components or devices;It is used to store, transmit and convert electromagnetic energy and information, or generate a magnetic field of certain intensity and distribution in a specific space;Sometimes it is also directly used in the natural form of materials (such asMagnetic fluid）。Magnetic materials play an important role in the field of electronic technology and other scientific and technological fields.
Sinan, a Compass in Ancient China
Magnetic material properties
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Materials with ferromagnetic properties have the following characteristics:
① Even if there is no external magnetic field, there is still permanent magnetic moment in each small area (magnetic domain) inside the material.However, when there is no external magnetic field, the magnetic moment direction of each magnetic domain of the unmagnetized magnetic material is randomly distributed, and its vector sum is zero, so the material is not magnetic as a whole.
② Easily magnetized.This is because the magnetic moment direction of each magnetic domain tries to turn to the magnetic field direction under the action of the external magnetic field, so a largeMagnetic inductionB。According to the formula B=μrBzero（BzeroIs the magnetic induction strength in vacuum), the relative permeability of magnetic materials μrIt's very big.In fact, μ of magnetic materialr10~10, but μ of non-magnetic materialr≈1。
③ There is a phenomenon of magnetic saturation, that is, B increases with H, but increases to a certain value BsAfter that, it no longer increases with H.BSIt is the magnetic materialSaturated magnetic induction。The saturation phenomenon occurs because the magnetic moments of all magnetic domains turn to the magnetic field direction after H reaches a certain value.For this reason, B and H are not linear, so the permeability is not constant, but related to the magnetic field strength.
④ There is hysteresis.I.eMagnetic inductionThe change of is lagging behind the change of magnetic field.[2]
