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What is soft magnetic material

What is soft magnetic material?

Soft magnetic material, refers to when the magnetization occurs at Hc not greater than 1000 A/m, such a material is called a soft magnet. A typical soft magnetic material can achieve the maximum magnetization strength with the smallest external magnetic field. Soft magnetic material is a magnetic material with low coercivity and high permeability.
Soft magnetic materials are easy to magnetize and demagnetize, and are widely used in electrical and electronic equipment. The most used soft magnetic materials are iron-silicon alloys (silicon steel sheet) and various soft magnetic ferrites.

20211007055049 67904 - What is soft magnetic material

Classification of soft magnetic materials by composition

(1) Pure iron and low carbon steel
The carbon content is less than 0.04%, including electromagnetically pure iron, electrolytic iron and carbonyl iron. It is characterized by high saturation magnetization strength, low price and good processing performance; however, its low resistivity and high eddy current loss in alternating magnetic field are only suitable for static use, such as manufacturing electromagnetic cores, pole boots, relays and speaker magnetic conductors, magnetic shields, etc.
(2) FeSi alloy
Silicon content 0.5% ~ 4.8%, generally made of thin plate, commonly known as silicon steel sheet. When silicon is added to pure iron, the magnetic properties of magnetic materials can be eliminated with the use of time. As the silicon content increases, the thermal conductivity decreases, the brittleness increases, and the saturation magnetization strength decreases, but its resistivity and permeability are high, and the coercivity and eddy current loss decrease, so that it can be applied to the field of AC, manufacturing motors, transformers, relays, mutual inductors, and other iron cores.
(3) FeAl alloy
Containing 6%-16% aluminum, it has good soft magnetic properties, high permeability and resistivity, high hardness, good wear resistance, but brittle, mainly used in the manufacture of small transformers, magnetic amplifiers, relays and other cores and magnetic heads, ultrasonic transducers, etc.
(4) FeSiAl alloy
It is obtained by adding silicon to binary iron-aluminum alloy. Its hardness, saturation magnetic induction strength, magnetic permeability and resistivity are high. The disadvantage is that the magnetic property is sensitive to the fluctuation of the composition, brittle, and poor processing performance. It is mainly used for audio and video heads.
(5) Nickel-iron system alloy
Nickel content of 30% to 90%, also known as PoMo alloy, through the alloying element ratios and appropriate processes, the magnetic properties can be controlled to obtain high permeability, constant permeability, moment magnetic and other soft magnetic materials. Its high plasticity and sensitivity to stress can be used as pulse transformer materials, inductor cores and functional magnetic materials.
(6) Iron-cobalt system alloy
Cobalt content 27%~50%. It has high saturation magnetization strength and low resistivity. Suitable for manufacturing pole boots, motor rotors and stators, small transformer cores, etc.
(7) Soft magnetic ferrite
Non-metallic subferromagnetic soft magnetic material. High resistivity (10-2 ~ 1010Ω-m ), lower saturation magnetization strength than metal, low price, widely used as inductive components and transformer components (see ferrite).
(8) Amorphous soft magnetic alloy
A non-long-range ordered, grain-free alloy, also known as metallic glass, or amorphous metal. Its high permeability and resistivity, small coercivity, insensitive to stress, there is no anisotropy of the magnetic crystal caused by the crystal structure, corrosion resistance and high strength and other characteristics. In addition, its Curie point is much lower than that of crystalline soft magnetic materials, and the electric energy loss is greatly reduced, which is a new type of soft magnetic material being developed and utilized.
(9) Super microcrystalline soft magnetic alloy
A soft magnetic material discovered in the 1980s. It is composed of crystalline phase less than 50 nm and amorphous grain boundary phase, which has better comprehensive performance than crystalline and amorphous alloy, not only high permeability, low coercivity, small iron loss, and high saturation magnetic induction strength and good stability. Now the main research is on iron-based super-microcrystalline alloys.

Performance parameters of soft magnetic materials

Saturated magnetic induction strength Bs: Its size depends on the composition of the material, and the physical state it corresponds to is the neat arrangement of the magnetization vector inside the material.
Residual magnetic induction strength Br: It is the characteristic parameter on the hysteresis line, the value of B when H returns to 0.
Rectangular ratio: Br∕Bs
Coercivity Hc: is the quantity that indicates the ease of magnetization of the material and depends on the composition of the material and defects (impurities, stresses, etc.).
Permeability μ: is the ratio of B to H corresponding to any point on the hysteresis line and is closely related to the device operating state.
Initial permeability μi, maximum permeability μm, differential permeability μd, amplitude permeability μa, effective permeability μe, and pulse permeability μp.
Curie temperature Tc: The magnetization strength of a ferromagnetic substance decreases with increasing temperature, and when it reaches a certain temperature, the spontaneous magnetization disappears and transforms into paramagnetism, and the critical temperature is the Curie temperature. It determines the upper limit temperature of the magnetic device work.
Loss P: Hysteresis loss Ph and eddy current loss Pe P = Ph + Pe = af + bf2+ c Pe ∝ f2 t2 /, ρ decreases.
The method to reduce the hysteresis loss Ph is to reduce the coercivity Hc; the method to reduce the eddy current loss Pe is to thin the thickness of the magnetic material t and increase the resistivity of the material ρ. The relationship between the loss of the core and the temperature rise of the core in free standing air is: total power dissipation (mW) / surface area (cm2)

Types, characteristics and applications of soft magnetic materials

Type Main features Scope of application
Electromagnetic pure iron
When the carbon content is less than 0.04%, the saturation magnetic induction is large and the cold workability is good. But resistivity
Small iron loss, magnetic aging phenomenon.
Generally used in DC magnetic field.
Silicon steel sheets
Compared with electrical pure iron, the resistivity increases, the iron loss decreases, and the magnetic aging is basically eliminated. But heat conduction.
When the coefficient decreases, the hardness increases and the brittleness increases.
Motor, transformer, relay, transformer, on.
Iron core of related products.
Ferronickel alloy
Compared with other soft magnetic materials, under weak magnetic field, the permeability is higher and the coercivity is smaller, but the stress is lower.
It’s sensitive.
The frequency is less than 1MHz and works in weak magnetic field.
Iron aluminum alloy
Compared with Fe Ni alloy, it has high resistivity, light weight and low permeability. With the increase of aluminum content.
The hardness and brittleness increase, and the plasticity becomes worse.
Devices working in weak and strong magnetic fields.
Soft ferrite
It is a sintered body formed by metal oxidation and ceramic process, with high resistivity and low eddy current loss.
The saturation magnetic induction intensity is small and the temperature stability is poor.
In high frequency or higher frequency range, the power is not too high
Large magnetic components.
Magnetic medium
It is made of metal soft magnetic material powder glued by insulating material, with low eddy current loss and stability.
Good, the price is high.

Working in low frequency or high frequency range under weak magnetic field.


New Soft Magnets

Soft Magnetic Ferrites

Soft magnetic ferrite is characterized by low saturation flux density, low permeability, low Curie temperature, low medium and high frequency losses, and low cost. The first three low are its disadvantages, limiting its use, and now (early 21st century) efforts are being made to improve them. The last two low are its advantages, which facilitate access to the high-frequency market, and now (early 21st century) efforts are being made to expand them.
Taking the loss at 100kHz, 0.2T and 100℃ as an example, TDK’s PC40 is 410mW/cm3, PC44 is 300mW/cm3, PC47 is 250mW/cm3. TOKIN’s BH1 is 250mW/cm3, and the loss is constantly decreasing. JP4E produced by Jinning in China also reaches 300mW/cm3.
TDK’s PC50 operates at 500kHz to 1MHz, FDK’s 7H20 and TOKIN’s B40 operate at 1MHz, and Philips’ 3F4, 3F45 and 3F5 all operate at over 1MHz. The operating frequency of DMR1.2K from East Magnetic even exceeds 3MHz, reaching 5.64MHz.
Magnetic permeability is the weak point of soft magnetic ferrite. Now (early 21st century) domestic production is generally around 10,000. Foreign TDK’s H5C5, Philips’ 3E9, reached 30,000 and 20,000 respectively.
The research on the synthesis of MnZn ferrite materials using SHS method is noteworthy. Experimental results with this method show that the manufacturing energy consumption and cost of ferrite can be greatly reduced. Successful experiments have been reported in China.

Amorphous and nanocrystalline alloys

Iron-based amorphous alloys are competing with silicon steel in the field of industrial and intermediate frequencies. Compared with silicon steel, iron-based amorphous alloys have the following advantages and disadvantages.

  • 1) The saturation flux density Bs of iron-based amorphous alloy is lower than that of silicon steel, however, at the same Bm, the loss of iron-based amorphous alloy is smaller than that of 3% silicon steel at 0.23mm thickness. It is generally believed that the reason for the small loss is the thin thickness and high resistivity of the iron-based amorphous alloy strip. This is only one aspect, but the main reason is that Fe-based amorphous alloys are amorphous, the atomic arrangement is random, there is no magnetic crystal anisotropy generated by the atomic orientation arrangement, and there is no grain boundary that generates local deformation and composition offset. Therefore, the energy barriers that prevent domain wall motion and magnetic moment rotation are very small and have unprecedented soft magnetism, so the permeability is high, the coercivity is small, and the loss is low.
  • 2) The filling factor of iron-based amorphous alloy cores is 0.84-0.86, compared with the filling factor of silicon steel 0.90-0.95, and the volume of iron-based amorphous alloy cores of the same weight is larger than that of silicon steel cores.
  • 3) The working flux density of iron-based amorphous alloy cores is 1.35T-1.40T, compared to 1.6T-1.7T for silicon steel. the weight of iron-based amorphous alloy IFT transformers is about 130% of the weight of silicon steel IFT transformers. However, even if the weight is heavy, for the same capacity of IFT transformer, the loss of core with iron-based amorphous alloy is 70%-80% lower than that with silicon steel.
  • 4) Assume that the load loss (copper loss) of IFT transformers are all the same and the load factor is also 50%. Then, to make the iron loss of silicon steel IFT transformers and iron-based amorphous alloy IFT transformers the same, the weight of silicon steel transformers is 18 times that of iron-based amorphous alloy transformers. Therefore, the general agreement of the domestic people put aside the loss level of the transformer, generalized talk about the weight, cost and price of iron-based amorphous alloy IFT transformer, is 130%-150% of the silicon steel IFT transformer, and does not meet the market requirements of the principle of performance to price ratio. Two methods of comparison are proposed abroad, one is to find out the weight and price of copper and iron materials used in the two IFT transformers under the same loss conditions for comparison. The other method is to reduce the loss of iron-based amorphous alloy IFB transformers by wattage, converted into money for compensation. No-load loss per watt is converted to $5-11, which is equivalent to RMB 42-92. Load losses per watt translate into $0.7-1.0, equivalent to RMB 6-8.3. For example, a 50Hz, 5kVA single-phase transformer with silicon steel core is quoted at RMB 1700/unit; no-load loss of 28W is RMB 1680 at RMB 60/W; load loss of 110W is RMB 880 at RMB 8/W; then, the total evaluated price is RMB 4260/unit. With iron-based amorphous alloy core, the quoted price is RMB 2500/unit; no-load loss is 6W, which is converted into RMB 360; load loss is 110W, which is converted into RMB 880; the total appraised price is RMB 3740/unit. If loss is not considered, the single calculation offer, 5kVA iron-based amorphous alloy industrial frequency transformer is 147% of silicon steel industrial frequency transformer. If loss is considered, the total appraised price is 89%.
  • 5) Now (early 21st century) test IFT power transformer core material loss, is carried out at a sinusoidal voltage with aberration less than 2%. And the actual IFB grid distortion is 5%. In this case, the iron-based amorphous alloy loss increases to 106% and the silicon steel loss increases to 123%. If the condition of high harmonics is large and the distortion is 75% (e.g. IFT rectifier transformer), the iron-based amorphous alloy loss increases to 160% and the silicon steel loss increases to more than 300%. It means that the iron-based amorphous alloy resistance to power waveform distortion is stronger than silicon steel.
  • 6) The magnetostriction coefficient of iron-based amorphous alloy is large, which is 3-5 times that of silicon steel. Therefore, the noise of iron-based amorphous alloy frequency transformer is 120% of the noise of silicon steel frequency transformer, which is 3-5dB larger.
  • 7) In the current market, the price of iron-based amorphous alloy strip is 150% of 0.23mm 3% oriented silicon steel, and about 40% of 0.15mm 3% oriented silicon steel (after special treatment).
  • 8) Iron-based amorphous alloy annealing temperature is lower than silicon steel, consuming less energy, and iron-based amorphous alloy cores are generally manufactured by specialized production plants. Silicon steel cores are generally manufactured by transformer manufacturing plants.

According to the above comparison, as long as a certain production scale, iron-based amorphous alloys will replace part of the silicon steel market in electronic transformers in the industrial frequency range. In the 400Hz to 10kHz medium frequency range, even if there are new varieties of silicon steel, iron-based amorphous alloys will still replace most of the silicon steel market below 0.15mm thickness.
It is worth noting that Japan is vigorously developing FeMB amorphous alloy and nanocrystalline alloy, its Bs up to 1.7-1.8T, and the loss of the existing FeSiB amorphous alloy of less than 50%, if used in industrial frequency electronic transformers, the working flux density of more than 1.5T, and the loss of only 10%-15% of the silicon steel industrial frequency transformers, will be a more powerful silicon steel industrial frequency transformers The competitor. Japan is expected in 2005 will be able to FeMB system amorphous alloy frequency transformer trial success, and into production.
Amorphous nanocrystalline alloys are competing with soft magnetic ferrites in the medium and high frequency field. In 10kHz to 50kHz electronic transformers, the working flux density of iron-based nanocrystalline alloys can reach 0.5T, and the loss P0.5/20k≤25W/kg, thus, there are obvious advantages in high-power electronic transformers. In 50kHz to 100kHz electronic transformers, iron-based nanocrystalline alloy loss P0.2/100k is 30-75W/kg, and iron-based amorphous alloy P0.2/100k is 30W/kg, which can replace part of the ferrite market.
Amorphous nanocrystalline alloy after more than 20 years of promotion and application, has proved to have the following advantages.

  • 1) No aging stability problem, nanocrystalline alloy at 200 ℃ or below, cobalt-based amorphous alloy at 100 ℃ or below, after long-term use, no significant changes in performance;
  • 2) Temperature stability is better than soft magnetic ferrite, the magnetic property changes 5%-10% in the range of -55℃ to 150℃, and it is reversible;

Soft magnetic composites

After debates, now (early 21st century) a consensus has been achieved on magnetic powder cores, etc., which is considered to be soft magnetic composites. Soft magnetic composites are formed by uniformly dispersing magnetic particles in non-magnetic materials. Compared with traditional metal soft magnetic alloys and ferrite materials, it has many unique advantages: magnetic metal particles are dispersed in non-conductor objects, which can reduce high frequency eddy current loss and increase application frequency; it can be processed into powder cores by both hot pressing method and injection molding into complex shaped magnets by using the current (early 21st century) plastic engineering technology; it has small density, light weight, high production efficiency, The advantages are low density, light weight, high production efficiency, low cost, and good product repeatability and consistency. The disadvantage is that the magnetic permeability is now (early 21st century) generally within 100 because the magnetic particles are separated from each other by non-magnetic bodies and the magnetic path is isolated. However, using nanotechnology and other measures, magnetic permeability exceeding 1000 and up to 6000 has been reported abroad.
The magnetic permeability of soft magnetic composites is influenced by many factors, such as the composition of magnetic particles, shape of particles, size, filling density, etc. Therefore, it can be adjusted according to the operating frequency.
Magnetic powder cores are typical examples of soft magnetic composites. Now (at the beginning of the 21st century) some soft magnetic ferrite has been replaced in inductors from 20 kHz to 100 kHz or even 1 MHz. An example is the iron-silicon aluminum magnetic powder core with 8.8% silicon and 5.76% aluminum, the remainder being entirely iron. The cores are made of 13×8×5 toroidal cores with silicone resin as adhesive and 1% stearic acid as lubricant under 2t/cm2 pressure and annealed in hydrogen at 673°K, 773°K and 873°K to achieve permeability of 100, 300 and 600 with low loss at 100kHz. It has been used instead of soft magnetic ferrite and MPP powder cores in inductors.
Soft magnetic composite materials for inductors for high power supplies, powder cores, have been developed and studied. Below 20 kHz, the magnetic permeability is essentially constant. At 1.0T, the permeability is about 100. 50Hz-20kHz loss is small, large cores of 100kg weight or more can be made, and in the audio range under 20kHz, the noise is 10dB lower than that of toroidal ferrite cores. can replace silicon steel and soft magnetic ferrite in high-power power supplies.
Cobalt/silicon dioxide (Co/SiO2) nanocomposite soft magnetic materials have been used to make large size cores different from thin films. The average size of cobalt particles is 30 μm and the filling degree is 40% to 90%. After stirring, the Co/SiO2 nanocomposite powder is formed by annealing and then pressed into a toroidal core. The magnetic permeability is up to 16 up to 300 MHz. the permeability of Ni-Zn ferrite is 12, and it decreases rapidly after 100 MHz. It proves that soft magnetic composites can also replace part of the ferrite market at high and ultra-high frequencies.

Difference between soft magnetic materials and hard magnetic materials

In a broad sense, any material that can respond to a magnetic field in some way is called a magnetic material.
It includes hard magnetic materials, soft magnetic materials, semi-hard magnetic materials, magnetostrictive materials, magneto-optical materials, magnetic bubble materials and magnetic refrigeration materials, etc. Among them, the most used are hard magnetic materials and soft magnetic materials.
Magnetic materials are generally divided into hard magnetic materials and soft magnetic materials according to the difficulty of their magnetization, and the difference between them mainly lies in.
Hard magnetic materials, also known as permanent magnetic materials, constant magnetic materials, is a wide hysteresis line, high coercivity, high remanence, once magnetized that can maintain a constant magnetic material. Commonly used hard magnetic materials are Alnico permanent magnet alloy, FeCrCo permanent magnet alloy, permanent magnet ferrite, rare earth permanent magnet material and composite permanent magnet material.
Soft magnetic materials are magnetic materials with low coercivity and high magnetic permeability. Soft magnetic materials are easy to magnetize and demagnetize, and are widely used in electrical and electronic equipment. The most applied soft magnetic materials are iron-silicon alloys (silicon steel sheet) and various soft magnetic ferrites.
The applications of hard magnetic materials are mainly as follows:

  • ① Applications based on the principle of electromagnetic force action are mainly: speakers, microphones, meters, buttons, motors, relays, sensors, switches, etc.
  • ② Applications based on the principle of magnetoelectric action are: magnetron and traveling wave tube and other microwave electronic tubes, picture tubes, titanium pumps, microwave ferrite devices, magnetoresistive devices, hall devices, etc.
  • ③ Applications based on the principle of magnetic action mainly include: magnetic bearings, mineral separators, magnetic separators, magnetic suction cups, magnetic seals, magnetic blackboards, toys, signs, combination locks, copiers, thermometers, etc. Other applications are: magnetic therapy, magnetized water, magnetic anesthesia, etc.

The main applications of soft magnetic materials are as follows:
Mainly used in magnetic antennas, inductors, transformers, magnetic heads, headphones, relays, vibrators, TV deflection yokes, cables, delay lines, sensors, microwave absorption materials, electromagnets, gas pedal high frequency acceleration cavities, magnetic field probes, magnetic substrates, magnetic field shielding, high frequency quenching and gathering, electromagnetic suction cups, magnetic sensitive components (such as magnetic heat materials for switches), etc.
Source: China Permanent Magnet Manufacturer –



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