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Soft magnetic

Introduction to terms

Magnetic materials with low coercivity, also known as high permeability materials. In the power industry, it is used to manufacture iron cores for electrical equipment such as motors and transformers. It is used to manufacture various magnetic components in the electronics industry and is widely used in television, broadcasting and communications. This kind of material has the characteristics of high saturation magnetic flux density, high magnetic permeability, long and narrow hysteresis loop, small area, low hysteresis loss, low remanence and coercive force. When used in AC applications, eddy current loss and hysteresis loss are required to be small. Commonly used are pure iron, low carbon steel, silicon steel sheet, permalloy, ferrite, etc.

(1) Pure iron, low carbon steel: high magnetic permeability and good processing performance. However, the eddy current loss is large, so it is only suitable for DC cores.

(2) Silicon steel sheet, silicon steel strip: high resistivity, low eddy current loss. But it is brittle and poor in processing performance. Sheets are laminated or rolled into a ring for use, and insulating varnish is impregnated between sheets or an oxide layer is formed to reduce eddy current loss.

(3) Permalloy: A general term for iron-nickel alloys, which have high magnetic permeability. Used in precision instruments, recording heads, etc. or where small size is required.

(4) Ferrite: Fe2O3 as the main component, mixed with Mn-Zn or Ni-Zn, etc., using powder The metallurgical method is used to press manganese-zinc ferrite or nickel-zinc ferrite, which has high resistivity and low high-frequency loss. The former is used for below 1MHz, and the latter is used for microwave frequencies. The higher the operating frequency, the lower the magnetic permeability. Ferrite is a ferrimagnetic material, and its permeability is lower than that of ferromagnetic materials.

When the magnetization occurs at Hc not greater than 1000A/m, such materials are called soft magnets. For typical soft magnetic materials, the maximum magnetization can be achieved with the smallest external magnetic field.

The main characteristics of soft magnetic materials: soft magnetic materials (soft magnetic materials) have low coercivity and high permeability magnetic materials. Soft magnetic materials are easy to magnetize and demagnetize, and are widely used in electrical and electronic equipment. The most widely used soft magnetic materials are iron-silicon alloys (silicon steel sheets) and various soft ferrites.

Classification application

Soft magnetic materials can be divided into three categories: metallic soft magnetic materials, ferrite soft magnetic materials and magnetic media. Among them, metal soft magnetic is divided into four types: electromagnetic pure iron, silicon steel sheet, iron-nickel alloy and iron-aluminum alloy.

The types, characteristics and application scope of soft magnetic materials are as follows.

< td>Soft ferrite p>
Types, characteristics and application scope of soft magnetic materials
TypesMain featuresApplication scope td>
Electromagnetic pure ironThe carbon content is below 0.04%, the saturation magnetic induction is large, and the cold workability is good. However, the resistivity is

small, iron loss is large, and there is magnetic aging.

Generally used in DC magnetic field
silicon steel sheet td> Compared with electrical pure iron, the resistivity is increased, the iron loss is reduced, and the magnetic aging is basically eliminated. However, the thermal conductivity is reduced, the hardness is increased, and the brittleness is increased.Iron cores of motors, transformers, relays, transformers, open

closed products

Iron-nickel alloyCompared with other soft magnetic materials, in a weak magnetic field, the permeability is large, the coercive force is small, but the stress is

More sensitive

Frequency is below 1MHz, working in a weak magnetic field


iron aluminum alloy< /td>Compared with iron-nickel alloy, it has higher resistivity, lighter weight, but lower magnetic permeability. With the increase of aluminum content

hardness and brittleness increase, plasticity becomes worse

devices working under weak and strong magnetic fields
is a sintered body formed by metal oxidation through ceramic technology, with extremely high resistivity and extremely low eddy current loss.

Saturation magnetic induction intensity is small, temperature stability is poor

In high frequency or higher frequency range, the power is not too large

Magnetic element

Magnetic mediumIt is made of metal soft magnetic material powder and insulating material glued together, eddy current loss is small, stability

good, high price

devices working under weak magnetic fields in the low-frequency or high-frequency range

Brief History of Development

< p>The application of soft magnetic materials in industry began at the end of the 19th century. With the rise of electric power and telecommunications technology, low-carbon steel has been used to manufacture motors and transformers, and fine iron powder, iron oxide, thin iron wires, etc. are used in the magnetic core of the inductor coil in the telephone line.

By the beginning of the 20th century, silicon steel sheets were developed to replace low-carbon steel, which improved the efficiency of transformers and reduced losses. Until now, the silicon steel sheet still ranks first in the soft magnetic materials used in the power industry.

In the 1920s, the rise of radio technology promoted the development of high-permeability materials, and permalloy and permalloy magnetic powder cores appeared.

From the 1940s to the 1960s, it was a period of rapid development of science and technology. The invention of radar, television broadcasting, integrated circuits, etc. had higher requirements for soft magnetic materials, and produced soft magnetic alloy thin films. Tape and soft ferrite materials.

In the 1970s, with the development of telecommunications, automatic control, and computer industries, soft magnetic alloys for magnetic heads were developed. In addition to traditional crystalline soft magnetic alloys, another type of material emerged ——Amorphous soft magnetic alloy.

Development trend

The rapid development of the electronic information industry has also put forward various new requirements for high-frequency inductance components (such as high-frequency transformers, small inductors, etc.). It is also required to improve and improve the performance of the ferrite core as the main component of the inductance element.

Therefore, higher material standards and requirements are also proposed for soft ferrite materials and magnetic core components, such as miniaturization, chip-type, high-frequency, high-performance, and low-loss components. Etc.

In soft ferrite, the materials that are currently in the greatest demand and the most urgent requirements for performance improvement are high-frequency low-power loss ferrite materials and high-permeability ferrite materials.

High frequency and low power loss ferrite materials are mainly used in various high frequency miniaturized switching power supplies (such as AC-DC, DC-AC converters) and display flyback transformers; high permeability High-speed ferrite materials are mainly used in broadband transformers, pulse transformers and anti-electromagnetic wave interference devices. According to reports, the output of these two materials has accounted for more than 60% of the total output of all soft ferrites.

The main requirements for power ferrite materials are: higher permeability (mi2000), high Curie temperature (T i>c), high apparent density (d), high saturation magnetic flux density (Bs) and ultra-low core loss under high frequency (P c). The main requirements for high permeability ferrite materials are: high permeability (mi12000), high apparent density (d), high frequency Low core loss under low field (tand/mi) and excellent frequency extension characteristics (f- L). The main requirements for the ferrite core components themselves are: the best electromagnetic performance and performance consistency, accurate mechanical dimensions and sufficient mechanical strength and good workmanship (including appearance quality and shape defects, etc.).

Looking at the changes in the production of soft ferrites in various countries in recent years, it can be seen that the production pattern of soft ferrites in the world has undergone great changes. In the next few years, although the production of soft ferrites in Japan, the United States and Western European countries will continue to maintain negative growth, in order to make full use of the cheap labor resources and raw material resources in the Asia-Pacific region, some companies in these countries, such as: Philips, Siemens, TDK, The output of ferrite factories (mainly producing MnZn ferrite) established in the region (mainly concentrated in China, Taiwan, India and Southeast Asian countries), such as TOKIN, FDK, Hitachi, and Sichuan Railways, has been increasing, and these companies The trend of shifting its production plants to Asia is also intensifying. The influx of ferrite factories in developed countries is bound to further intensify the competition in the production of soft ferrite in the region.

In short, soft magnetic materials will continue to follow high Bs, high m, high Tc, low Pc, lowHc and high frequency, miniaturization, and thinning are developing to meet the trend of increasingly thin film, miniaturization, and even integration of magnetic components .

In the next 10 years, soft ferrite materials will focus on the development of high-frequency, low-power, high-permeability materials and chip surface mount components; in amorphous soft magnetic alloys and magnetic recording In terms of materials and high-frequency soft magnetic alloys, the focus is on the development of nano-materials.

In the development process of soft magnetic materials, metal soft magnetic dominates the world before the 1930s, and the golden age of soft ferrites in the 1950s and 1960s; since the successful development of amorphous materials in the early 1970s Since the successful development of nanocrystalline soft magnetic materials in the late 1980s, many nanocrystalline soft magnetic materials with high initial permeability and low coercivity have been discovered. In recent years, many nanocrystalline soft magnetic materials with excellent high-frequency characteristics have been developed. Nano-particle structure of soft magnetic materials.

Since the 1990s, the rise of nano-structured metallic magnetic materials has become a strong competitor of soft ferrites. At present, traditional ferrite soft magnetic materials are developing in the direction of improving comprehensive performance indicators.

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