What Is Magnetism?
The nature of a mineral attracted or repelled by an external magnetic field is called its magnetism. In general, the repulsive force of minerals by magnetic fields is very weak. Therefore, the magnetism referred to in the identification, sorting and general study of minerals mainly refers to the nature of minerals attracted by external magnetic fields. [1]
- As early as 1820, Danish scientist Oster discovered
- To put it simply, magnetism means that a substance is subjected to an uneven magnetic field.
- Generally speaking, the magnetic properties of matter can be divided into
- Magnetic materials have magnetically ordered ferromagnetic substances. In a broad sense, they also include weakly magnetic and antiferromagnetic substances to which their magnetic and magnetic effects can be applied. Magnetism is a basic property of matter. Substances can be divided into antimagnetic, paramagnetic, ferromagnetic, antiferromagnetic, and ferrimagnetic substances according to their internal structure and their properties in an external magnetic field. Ferromagnetic and ferrimagnetic materials are ferromagnetic materials, and diamagnetic and paramagnetic materials are weak magnetic materials. Magnetic materials are divided into metal and non-metal according to their properties. The former are mainly electrical steel, nickel-based alloys and rare earth alloys, and the latter are mainly ferrite materials. According to use, it is divided into soft magnetic materials, permanent magnetic materials and functional magnetic materials. Functional magnetic materials mainly include magnetostrictive materials, magnetic recording materials, magnetoresistive materials, magnetic bubble materials, magneto-optical materials, magneto-rotary materials, and magnetic thin film materials, etc., reflecting the basic magnetic properties of magnetic materials are magnetization curves and hysteresis loops. And magnetic loss.
- 1. Permanent magnet material
- Once the permanent magnetic material is magnetized by the external magnetic field, it can maintain one or most of the magnetism in the original magnetization direction even under the action of a considerable reverse magnetic field. The requirements for such materials are high residual magnetic induction B r, high coercive force B H C (that is, the anti-demagnetization ability of magnetic materials), and large magnetic energy product ( B H ) (that is, the magnetic field energy provided to space). Compared with soft magnetic materials, it is also called hard magnetic materials.
- There are three types of permanent magnet materials: alloys, ferrites and intermetallic compounds. alloys: including casting, sintering and machinable alloys. The main varieties of cast alloys are: AlNi (Co), FeCr (Co), FeCrMo, FeAlC, FeCo (V) (W); sintered alloys include: Re-Co (Re stands for rare earth element), Re-Fe, and AlNi (Co ), FeCrCo, etc .; Machinable alloys include: FeCrCo, PtCo, MnAlC, CuNiFe, and AlMnAg, etc., the lower two of the latter two are also called semi-permanent magnet materials. Ferrites: The main component is MO · 6
- There are many uses for permanent magnet materials: Applications based on the principle of electromagnetic force are: speakers, microphones, meters, buttons, motors, relays, sensors, switches, etc. The applications based on the principle of magnetoelectricity are: microwave electron tubes such as magnetrons and traveling wave tubes, picture tubes, titanium pumps, microwave ferrite devices, magnetoresistive devices, Hall devices, etc. The applications based on the principle of magnetic force are mainly: magnetic bearings, ore dressing machines, magnetic separators, magnetic suction cups, magnetic seals, magnetic blackboards, toys, signs, password locks, copiers, temperature controllers, etc. Other applications include: magnetic therapy, magnetized water, and magnetic anesthesia.
- According to the needs of use, permanent magnet materials can have different structures and shapes. Some materials also differ in isotropy and anisotropy.
- 2. Soft magnetic material
- Its function is mainly the conversion and transmission of magnetic permeability and electromagnetic energy. Therefore, such materials are required to have high magnetic permeability and magnetic induction strength, and at the same time, the area or magnetic loss of the hysteresis loop should be 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.
- A kind of soft magnetic material-iron powder core
- Soft magnetic materials can be roughly divided into four categories. Alloy thin strip or sheet: FeNi (Mo), FeSi, FeAl, etc. Amorphous alloy ribbon: Fe-based, Co-based, FeNi-based or FeNiCo-based, etc., with appropriate Si, B, P and other doping elements, also known as magnetic glass. Magnetic medium (iron powder core): FeNi (Mo), FeSiAl, carbonyl iron, and ferrite and other powders are covered and bonded with an electrically insulating medium and then pressed and formed as required. Ferrite: including spinel typeMO ·
- Soft magnetic materials are widely used, mainly for magnetic antennas, inductors, transformers, magnetic heads, headphones, relays, vibrators, TV deflection yoke, cables, delay lines, sensors, microwave absorbing materials, electromagnets, and accelerators for high-frequency acceleration. Cavity, magnetic field probe, magnetic substrate, magnetic field shielding, high-frequency quenching energy gathering, electromagnetic chuck, magnetic sensor (such as magnetic thermal material as a switch), etc.
- 3 Ferromagnetic materials and magnetic recording materials
- It is mainly used for information recording, contactless switch, logic operation and information amplification. This material is characterized by a rectangular hysteresis loop.
- 4 Gyromagnetic material
- It has unique microwave magnetic properties, such as the tensor characteristics of magnetic permeability, Faraday rotation, resonance absorption, field shift, phase shift, birefringence, and spin wave effects. The devices designed according to this are mainly used for the transmission and conversion of microwave energy. Commonly used are isolator, circulator, filter (fixed or ESC), attenuator, phase shifter, modulator, switch, limiter and Delay lines, etc., as well as magnetic surface wave and magnetostatic wave devices under development (see Microwave Ferrite Devices). Commonly used materials have been formed into series, including Ni-based, Mg-based, Li-based, YlG-based and BiCaV-based ferrite materials; and can be made into different structures such as single crystal, polycrystal, amorphous or thin film according to the needs of the device And form.
- 5. Piezomagnetic material
- This type of material is characterized by mechanical deformation under the action of an external magnetic field, so it is also called magnetostrictive material, and its function is to convert magnetic sound or magnetic energy. Commonly used in the vibration head of ultrasonic generators, mechanical filters of telecommunications machines and electrical pulse signal delay lines, etc., combined with microwave technology can make micro-acoustic (or rotary sound) devices. Due to the high mechanical strength of the alloy material and its resistance to vibration without exploding, the vibrating head is mostly made of Ni-based and NiCo-based alloys; when it is used under small signals, Ni-based and NiCo-based ferrites are mostly used. New types of stronger piezomagnetism in amorphous alloys are suitable for making delay lines. The production and application of piezomagnetic materials are far less than the first four materials.
- Application of magnetic materials-transformers
- Magnetic materials are widely used in production, life, and 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 sensitizers in communication technology, magnetic mines, electromagnetic cannons in defense technology, various household appliances, etc. . In addition, magnetic materials have also been widely used in geological and mineral exploration, marine exploration, and new information, energy, biological, and space technologies. The use of magnetic materials is wide. It mainly uses 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 to generate a certain strength and distributed magnetic field in a specific space; sometimes it is directly based on the natural form of the material Utilization (such as magnetic liquid). Magnetic materials have an important role in the field of electronic technology and other scientific and technological fields. [4]