NdFeB magnetic material encyclopedia

- Nov 03, 2017 -

NdFeB basic characteristics

1, the magnetization curve of magnetic materials

   The magnetic material is made of ferromagnetic material or ferrimagnetic material. Under the action of an applied magnetic field H, there must be a corresponding magnetization M or magnetic induction B. The curve of the variation with the magnetic field strength H is called the magnetization curve Or B ~ H curve). Magnetization curve is generally non-linear, with two characteristics: magnetic saturation and hysteresis phenomenon. 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 magnetic field H is reduced to zero after the M value of the material reaches saturation, Not restored to zero, but changes along the MsMr curve. The working state of the material is equivalent to a certain point on the M ~ H curve or the B ~ H curve, which is often called the working point.


2. the common magnetic properties of soft magnetic materials parameters

   Saturation magnetic flux density Bs: its size depends on the composition of the material, which corresponds to the physical state of the material within the magnetization vector neatly arranged.

   The residual magnetic flux density Br: is the characteristic parameter on the hysteresis loop, H returns to 0 when the B value.

   Rectangular ratio: Br / Bs

   Coercivity Hc: is the amount of material that indicates the ease of magnetization, depending on the material composition and defects (impurities, stress, etc.).

   Magnetic permeability μ: Hysteresis loop is any point corresponding to the ratio of B and H, and the device is closely related to working conditions.

   Initial magnetic permeability μi, maximum magnetic permeability μm, differential magnetic permeability μd, amplitude magnetic permeability μa, effective magnetic permeability μe, and pulse magnetic permeability μp.

   Curie temperature Tc: The magnetization of a ferromagnetic substance decreases with increasing temperature. When a certain temperature is reached, spontaneous magnetization disappears and changes to paramagnetic. The critical temperature is the Curie temperature. It determines the maximum working temperature of the magnetic device.

   Loss P: hysteresis loss Ph and eddy current loss Pe P = Ph + Pe = af + bf2 + c Pe α f2 t2 /, ρ decreases, reducing hysteresis loss Ph method is to reduce the coercive force Hc; method to reduce eddy current loss Pe Is to reduce the thickness of the magnetic material t and increase the material resistivity ρ. The relationship between core loss and core temperature rise in free still air is: Total power dissipation (mW) / surface area (cm2)


3. the magnetic parameters of soft magnetic materials and the conversion of the electrical parameters of the device


   In the design of soft magnetic devices, we must first determine the device's voltage ~ current characteristics according to the requirements of the circuit. The voltage-current characteristics of the device are closely related to the geometry and magnetization of the core. The designer must be familiar with the magnetization process of the material and master the conversion of the material's magnetic parameters to the device's electrical parameters. Design of soft magnetic devices usually consists of three steps: the correct choice of magnetic materials; reasonably determine the geometry and size of the core; according to the magnetic parameters, the simulation of the working state of the core to obtain the corresponding electrical parameters.


NdFeB classification

Magnetic materials have a magnetically ordered ferromagnetic substance, and in a broad sense, also include weakly magnetic and antiferromagnetic substances to which magnetic and magnetic effects can be applied. Magnetism is a basic property of matter. Materials according to their internal structure and characteristics of the external magnetic field can be divided into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferrimagnetic material. Ferromagnetic and ferrimagnetic materials are ferromagnetic materials, diamagnetic and paramagnetic materials are weak magnetic materials. According to the nature of the magnetic material is divided into two types of metals and non-metallic, the former mainly electrical steel, nickel-based alloys and rare earth alloys, the latter is mainly ferrite material. According to use is divided into soft magnetic materials, permanent magnetic materials and functional magnetic materials. Functional magnetic materials include magnetostrictive materials, magnetic recording materials, magnetoresistance materials, bubble materials, magneto-optical materials, gyromagnetic materials and magnetic thin film materials, magnetization curves that reflect basic magnetic properties of magnetic materials, hysteresis loops And magnetic loss and so on.


1. permanent magnet material after the external magnetic field magnetization, even in the role of a considerable reverse magnetic field, still able to maintain one or most of the original magnetization of the magnetic direction. The requirements for this type of material are the remanent magnetic flux density, Br, coercive force, BHC, that is, the magnetic material has high demagnetization resistance, and the magnetic energy product (BH), that is, the magnetic field energy provided to the space. It is also referred to as a hard magnetic material relative to a soft magnetic material. Soft magnetic materials products

Permanent magnet materials are alloys, ferrites and intermetallics three categories. ① alloy categories: including casting, sintering and machinable alloys. The main cast alloys are AlNi (Co), FeCr (Co), FeCrMo, FeAlC and FeCo (V) (W). Sintered alloys are Re-Co (Re represents RE), Re-Fe and AlNi ), FeCrCo, etc .; Machinable alloys are: FeCrCo, PtCo, MnAlC, CuNiFe and AlMnAg, etc., the latter two in the lower BHC also known as semi-permanent magnetic materials. ② ferrite: the main component of MO · 6Fe2O3, M represents Ba, Sr, Pb or SrCa, LaCa and other composite components. ③ intermetallic compounds: mainly represented by MnBi.

Permanent magnet materials have many uses. ① based on the principle of electromagnetic force applications are: speakers, microphones, meters, buttons, motors, relays, sensors, switches and so on. ② based on the principle of magnetoelectric effect of the main applications are: magnetron and traveling wave tube microwave tubes, picture tubes, titanium pumps, microwave ferrite devices, magnetoresistive devices, Hall devices. ③ based on the principle of magnetic force applications are: magnetic bearings, concentrator, magnetic separator, magnetic sucker, magnetic seal, magnetic blackboard, toys, signs, password locks, copiers, temperature control and so on. Other applications are: magnetic therapy, magnetized water, magnetic anesthesia and so on.

According to the needs of use, permanent magnet materials can have different structures and forms. Some materials are also different from isotropy and anisotropy.


2. soft magnetic materials, permanent magnetic materials


Its main function is the magnetic conductivity, electromagnetic energy conversion and transmission. Therefore, these materials require high permeability and magnetic induction, while hysteresis loop area or magnetic loss should be small. In contrast to permanent magnets, the smaller the Br and BHC, the better, but the greater the saturation magnetic flux density, Bs, the better.

A kind of soft magnetic material - iron powder core

Soft magnetic materials can be roughly divided into four categories. ① alloy ribbon or sheet: FeNi (Mo), FeSi, FeAl and so on. ② amorphous alloy ribbon: Fe-based, Co-based, FeNi-based or FeNiCo-base with the appropriate Si, B, P and other doping elements, also known as magnetic glass. ③ magnetic media (iron powder core): FeNi (Mo), FeSiAl, carbonyl iron and ferrite and other powder, coated with electrical insulation and bonding press after pressing forming. ④ ferrite: spinel ─ ─ ─ ─ Fe · Fe2O3 (M on behalf of NiZn, MnZn, MgZn, Li1 / 2Fe1 / 2Zn, CaZn and so on), magnetoplumbite ─ ─ Ba3Me2Fe24O41 (Me on behalf of Co, Ni, Mg, Zn, Cu and their composite components). Soft magnetic materials are widely used in magnetic antennas, inductors, transformers, heads, earphones, relays, vibrators, TV deflection yokes, cables, delay lines, sensors, microwave absorbing materials, electromagnets, accelerators, Cavity, magnetic field probe, magnetic substrate, magnetic field shield, high-frequency quenching energy, electromagnetic sucker, magnetic sensors (such as magnetic material for the switch) and so on.


3. Moment of magnetic materials and magnetic recording materials

Mainly used for information recording, contactless switches, logic operations and information amplification. This material is characterized by a hysteresis loop rectangular.


4. Magnetic rotation material

It has unique microwave magnetic properties such as tensor properties 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. Isolators, circulators, filters (fixed or electric modulation), attenuators, phase shifters, modulators, switches and limiters are commonly used Delay lines, there are still developing magnetic surface wave and magnetostatic wave devices (see microwave ferrite devices). Commonly used materials have been formed series, Ni series, Mg series, Li series, YlG series and BiCaV series ferrite materials; and according to the needs of the device made of single crystal, polycrystalline, amorphous or thin film and other different structures And form.


5. pressure magnetic materials

Such materials are characterized by mechanical deformation under the action of an applied magnetic field, it is also known as magnetostrictive material, its function is to make magnetic or magnetic energy conversion. Commonly used in ultrasonic generator vibration head, mechanical filter and electrical pulse signal delay line, etc., combined with microwave technology can produce micro-acoustic (or whirling) devices. Due to the high mechanical strength alloy materials, anti-vibration and not burst, so the vibration head with Ni and NiCo alloys; Niu and NiCo ferrites are mostly used in small signals. Emerging in amorphous alloys are more strong magnetic varieties, suitable for the production of delay line. The production and application of piezomagnetic materials are far less than the previous four materials.

Applications of Magnetic Materials - Transformers

Magnetic material is a widely used material in production, life and national defense science and technology. Such as various motors and transformers in power technology, various magnetic components and microwave tubes in electronic technology, filters and sensors in communications technology, magnetic miners in defense technology, electromagnetic guns, various household appliances, etc. . In addition, magnetic materials are also widely used in geology and mineral exploration, marine exploration and new information, energy, biology and space technologies. Magnetic materials are widely used. Mainly by its various magnetic properties and special effects made of components or devices; used to store, transmit and convert electromagnetic energy and information, or in a particular space to produce a certain intensity and distribution of magnetic field; sometimes also in the natural form of the material directly Use (such as magnetic fluid). Magnetic materials in the field of electronic technology and other science and technology have an important role.


Article from NdFeB Industry Network

Related Products