Characteristics of various magnetic materials and applications of magnetic materials

Modern magnetic materials have been widely used in our lives, such as permanent magnet materials for motors, iron core materials for transformers, magneto-optical disks for memory, magnetic recording floppy disks for computers and so on. Generally speaking, magnetic materials refer to substances in which excessive elements such as iron, cobalt, nickel and their alloys can directly or indirectly produce magnetism. Magnetic materials can be divided into soft magnetic materials and hard magnetic materials according to the difficulty of demagnetization after magnetization. Let's talk about the related knowledge of magnetic materials first.

Magnetic materials include strong magnetic substances with magnetic order, and in a broad sense, weak magnetic and antiferromagnetic substances that can apply their magnetic and magnetic effects. Magnetism is the basic property of matter. According to its internal structure and properties in external magnetic field, substances can be divided into diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism and ferrimagnetism. Ferromagnetic and ferrimagnetic substances are strong magnetic substances, while diamagnetic and paramagnetic substances are weak magnetic substances. Magnetic materials can be divided into metal and nonmetal according to their properties. The former mainly includes electrical steel, nickel-based alloy and rare earth alloy, while the latter is mainly ferrite material. It can be divided into soft magnetic materials, permanent magnetic materials and functional magnetic materials according to their uses. Functional magnetic materials mainly include magnetostrictive materials, magnetic recording materials, magnetoresistance materials, bubble materials, magneto-optical materials, gyromagnetic materials and magnetic thin film materials. The basic magnetism of magnetic materials includes magnetization curve, hysteresis loop and magnetic loss.

Characteristics of various magnetic materials

1. Permanent magnet material

Once magnetized by an external magnetic field, one or most of the original magnetization direction can be maintained even under the action of a considerable reverse magnetic field. The requirements for this kind of materials are high remanence induction Br, strong coercivity BHC (ie, anti-demagnetization ability) and large magnetic energy product BH (ie, magnetic field energy provided to space). Compared with soft magnetic materials, it is also called hard magnetic materials.

Permanent magnet materials include alloys, ferrites and intermetallic compounds. ① Alloys: including casting, sintering and machinable alloys. The main varieties of casting alloys are: AlNi(Co), FeCr(Co), FeCrMo, FeAlC, FeCo (V) (W); Sintered alloy has: Re-Co (RE stands for rare earth element), Re-Fe, AlNi(Co), FeCrCo, etc. Machinable alloys include FeCrCo, PtCo, MnAlC, CuNiFe and AlMnAg, and the lower BHC of the latter two is also called semi-permanent magnet material. ② Ferrite: the main component is Mo 6Fe2O3, and m represents Ba, Sr, Pb or composite components such as SrCa and LaCa. ③ Intermetallic compounds: mainly represented by MnBi.

Permanent magnet materials have many uses. ① Applications based on the principle of electromagnetic force mainly include: speakers, microphones, electric meters, buttons, motors, relays, sensors, switches, etc. ② The applications based on magnetoelectric principle mainly include magnetron, traveling wave tube and other microwave tubes, picture tubes, titanium pumps, microwave ferrite devices, magnetoresistance devices, Hall devices and so on. ③ Applications based on the principle of magnetism mainly include: magnetic bearings, concentrators, magnetic separators, magnetic suction cups, magnetic seals, magnetic blackboards, toys, signs, coded locks, photocopiers, temperature controllers, etc. Other applications include: magnetic therapy, magnetized water, magnetic anesthesia, etc.

Permanent magnet materials can have different structures and shapes according to the needs of use. There are also differences between isotropic and anisotropic materials.

2. Soft magnetic materials

Its function is mainly the conversion and transmission of magnetic conduction and electromagnetic energy. Therefore, this kind of material is required to have high permeability and magnetic induction strength, and at the same time, the area or magnetic loss of hysteresis loop is required to be small. Contrary to permanent magnet materials, the smaller the Br and BHC, the better, but the larger the saturation magnetic induction intensity Bs.

Soft magnetic materials can be generally divided into four categories.

① Alloy strip or sheet: FeNi(Mo), FeSi, FeAl, etc.

② Amorphous alloy belt: iron-based, cobalt-based, FeNi-based or FeNiCo-based, with appropriate doping elements such as Si, B and P added, also called magnetic glass.

③ Magnetic medium (iron powder core): powder materials such as FeNi(Mo), FeSiAl, carbonyl iron, ferrite, etc., which are coated and bonded with electrical insulating medium and pressed into shape as required.

④ Ferrite: including spinel type ──m++ O fe2o 3(m++ stands for NiZn, MnZn, MgZn, Li 1/2Fe 1/2Zn, CaZn, etc. ) and magnesite type ── Ba3Me24O4 1 (Me stands for cobalt, nickel, magnesium, etc.

Soft magnetic materials are widely used in magnetic antennas, inductors, transformers, magnetic heads, earphones, relays, vibrators, TV deflection coils, cables, delay lines, sensors, microwave absorbing materials, electromagnets, high-frequency accelerating cavities of accelerators, magnetic field probes, magnetic substrates, magnetic shielding, high-frequency quenching energy gathering, electromagnetic suction cups, magnetic sensitive elements (such as magneto-thermal materials as switches) and so on.

3. Rectangular magnetic materials and magnetic recording materials

It is mainly used for information recording, contactless switching, logic operation and information amplification. This material is characterized by a rectangular hysteresis loop.

4. Gyromagnetic materials

It has unique microwave magnetism, such as tensor characteristics of permeability, Faraday rotation, * * * vibration absorption, field displacement, phase shift, birefringence and spin wave effect. Devices designed on this basis are mainly used for transmission and conversion of microwave energy, such as isolators, circulators, filters (fixed or electrically adjustable), attenuators, phase shifters, modulators, switches, limiters and delay lines, as well as magnetic surface wave and magnetostatic wave devices that are still under development (see microwave ferrite devices). A series of commonly used materials have been formed, including ferrite materials such as Ni series, Mg series, Li series, YlG series and BiCaV series. It can be made into different structures and shapes such as single crystal, polycrystalline, amorphous or thin film according to the needs of devices.

5. Piezoelectric materials

This material is characterized by mechanical deformation under the action of external magnetic field, so it is also called magnetostrictive material. Its function is to convert magnetic sound or magnetic energy. It is often used in vibration head of ultrasonic generator, mechanical filter of communication machine and delay line of electric pulse signal. Combined with microwave technology, micro-acoustic (or rotary acoustic) devices can be made. Ni-based and NiCo-based alloys are mostly used in vibration heads because of their high mechanical strength, anti-vibration and non-bursting. Nickel-based ferrite and nickel-cobalt-based ferrite are mostly used for small signals. A new amorphous alloy with strong piezomagnetism is suitable for making delay lines. The production and application of piezomagnetic materials are far less than the first four materials.

Application of magnetic materials

Magnetic materials are widely used in production, life and national defense science and technology. Such as manufacturing various motors and transformers in power technology, various magnetic components and microwave tubes in electronic technology, filters and inductors in communication technology, magnetic mines and electromagnetic guns in national defense technology, and various household appliances. In addition, magnetic materials are also widely used in geological and mineral exploration, marine exploration and new technologies in the fields of information, energy, biology and space.