In recent years, magnetic materials have been widely used in our life. For example, the permanent magnet material is used as the motor, the core material used in the transformer, as the magnetic disc used in memory, the computer USES magnetic recording floppy disk and so on. It is generally believed that magnetic materials refer to substances that can produce magnetism directly or indirectly by excessive elements Fe, Co, Ni and their alloys. Magnetic materials can be divided into soft magnetic materials and hard magnetic materials after magnetization. Now let's talk about the knowledge of magnetic materials.
Magnetic materials have magnetic and ordered magnetic properties, which also include weakly magnetic and anti-ferromagnetic substances which can be used for their magnetic and magnetic effects. Magnetism is an essential property of matter. According to its internal structure and the characteristics of its external magnetic field, the material can be divided into diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism and ferromagnetic substance. Ferromagnetism and ferromagnetism are strongly magnetic substances, and the diamagnetic and paramagnetic substances are weakly magnetic materials. The magnetic material is divided into two types: metal and non-metal. The former is mainly electrical steel, nickel base alloy and rare earth alloy, etc. The latter is mainly ferrite material. It is divided into soft magnetic materials, permanent magnetic materials and functional magnetic materials. Functional magnetic materials mainly include magnetostrictive materials, magnetic recording materials, magnetic resistance material, magnetic bubble material, magneto optical materials, magnetic materials and magnetic thin film materials, the reaction of basic magnetic magnetic materials can have magnetization curve and hysteresis loop and magnetic loss, etc.
Properties of different magnetic materials:
1. Permanent magnetic material
Once the external magnetic field is magnetized, the magnetism of one or most of the original magnetization can be maintained even under a considerable reverse magnetic field. The requirement for this kind of material is that the residual magnetic induction intensity is high, the coercivity BHC(i.e. anti-demagnetizing ability) is strong, and the magnetic material (BH) magnetic material (that is, the magnetic field energy provided by the space) is large. It is also known as a hard magnetic material relative to a soft magnetic material.
Permanent magnetic materials include alloy, ferrite and intermetallic compounds. Alloy: includes casting, sintering and machining alloys. The main types of casting alloys are :AlNi(Co), FeCr(Co), FeCrMo, FeAlC, FeCo(V)(W). Sintered alloys include Re-Co (Re represents rare earth elements), Re-Fe and AlNi (Co), FeCrCo, etc. The processing alloys include FeCrCo, PtCo, MnAlC, CuNiFe and AlMnAg, etc. The latter two types of BHC are also known as semi-permanent magnetic materials. The main components are MO·6Fe2O3,M represents Ba, Sr, Pb or SrCa, LaCa and other composite components. The metallic intermetallic compounds: mainly represented by MnBi.
Permanent magnetic materials have many USES. Based on the principle of electromagnetism, the application mainly includes: loudspeaker, microphone, electric meter, key, motor, relay, sensor, switch and so on. Based on the principle of magnetoelectric effect, the main applications include: magnetron and travel-wave tube, such as microwave tube, picture tube, titanium pump, microwave ferrite device, magnetic resistance device, hall device, etc. (3) based on the application of magnetic mechanism mainly include: magnetic bearings, separator, magnetic separator, magnetic chuck, magnetic seal, magnetic blackboard, toys, signs, combination lock, copy machine, temperature control meter, etc. Other applications include: magnetic therapy, magnetized water, magnetic anesthesia, etc.
According to the need of use, permanent magnet material can have different structure and form. Some materials are isotropic and anisotropic.
2. Soft magnetic materials
Its functions are mainly the transfer and transmission of magnetic and electromagnetic energy. Therefore, high permeability and magnetic induction intensity are required for this kind of material, and the area or magnetic loss of the hysteresis loop is small. In contrast to permanent magnetic materials, the smaller the Br and BHC are, the better the saturation magnetic induction intensity Bs is.
Soft magnetic materials can be broadly classified into four categories.
a)Thin strips or thin slices: FeNi(Mo), FeSi, FeAl, etc.
b)Non-crystalline alloy thin bands :Fe, Co, FeNi or FeNiCo, etc. with appropriate Si, B, P and other doping elements, also known as magnetic glass.
c)The magnetic medium (iron powder core) :FeNi(Mo), FeSiAl, carbonyl iron and ferrite and other powder materials, after being coated and bonded by electric insulating medium, press the shape according to the requirements.
d) ferrite: including spinel ─ ─ M++ o. Fe2O3 (M++ NiZn, MnZn, MgZn, Li1/2 fe1/2 zinc, CaZn, etc.), magnetic type lead stone ─ ─ Ba3Me2Fe24O41 (Me on behalf of Co and Ni, Mg, zinc, Cu and its composite components).
Applications of soft magnetic materials, mainly used in magnetic antenna, inductors, transformers, magnetic head, headphones, relay, vibrator, deflection yoke, cable TV, delay line, sensors, microwave absorbing materials, electromagnet, accelerator high-frequency acceleration cavity, probe, magnetic substrate, magnetic shielding, high frequency quenching shaped, magnetic chuck, magnetic sensor (such as magnetic thermal materials for switch).
3. Torque magnetic materials and magnetic recording materials.
Mainly used as information record, no contact switch, logic operation and information amplification. The characteristic of this material is that the hysteresis loop is rectangular.
4. Rotating magnetic material
It has unique microwave magnetism, such as tensor characteristic of magnetic permeability, Faraday rotation, resonance absorption, field shift, phase shift, birefringence and spin wave. According to the design of the device is mainly used as microwave power transmission and transformation, commonly used have isolator, circulator, filter (stationary or electric mode), attenuator, phase shifter, modulator, switch, the limiter and delay line, etc., and is still in the development of magnetic surface wave and static magnetic wave device (see microwave ferrite devices). The commonly used materials have formed a series of ferrite materials such as Ni, Mg, Li, YlG and BiCaV. The structure and morphology of single crystal, polycrystalline, amorphous or thin film can be made according to the requirements of the device.
5. Piezomagnetic material
This kind of material is characterized by mechanical deformation under the effect of external magnetic field, so it is also called magnetostrictive material. Its function is the conversion of 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, etc., which can be combined with microwave technology to make micro-sound (or rotary sound) devices. Due to the high mechanical strength of the alloy material, the vibration resistance is not cracked, so the vibration head multi-purpose Ni and NiCo alloy; Use the Ni and NiCo ferrites in small signals. In the amorphous alloy, there is a kind of strong piezoelectric variety, suitable for the production delay line. The production and application of piezoelectric materials are far less than those of the previous four materials.
6. Application of magnetic materials.
Magnetic materials are widely used in production, life and defense science and technology. Such as manufacturing power technology of all kinds of motors, transformers, all kinds of magnetic components in electronic technology and microwave tube, communication technology and intensifying of the filter, magnetic mine of defence technology, the electromagnetic gun, all kinds of household electrical appliances, etc. In addition, magnetic materials have been widely used in geological prospecting, ocean exploration and information, energy, biology and space technology.