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Difference between soft magnetic and hard magnetic materials

When we talk about permanent ferrite, we often mention soft magnetic ferrite, and then some customers ask: What is soft magnetism? Soft magnetic does not seem soft, but why is it called "soft" magnetism? Which are soft magnets? What's the difference between it and hard magnetism(permanent magnet)?

What is soft magnetism?

Soft magnetic materials, especially when magnetization occurs at Hc less than 1000A/m, coercivity is small, easy to magnetize and demagnetize magnetic materials. The "soft" in soft magnetism refers to the "soft" magnetic performance of these materials. In general, soft magnets also exhibit the normal properties of permanent magnets. But when the ordinary permanent magnet is very close to the conical tip of the soft magnet, the direction of the magnetic moment of the soft magnetic material changes, and the repulsive force of the two will suddenly change into an attractive force.

Soft magnetic materials have a wide range of uses. Because they are easy to magnetize and demagnetize, they have a high magnetic permeability and can play a good role in gathering magnetic field lines. Soft magnetic materials are widely used as the path of magnetic force lines, that is, as magnetic conductive materials, such as transformers, sensors, core magnetic shielding covers, special magnetic circuit, etc. The most widely used soft magnetic materials are iron-silicon alloy (silicon steel sheet) and various soft magnetic ferrites.

What is hard magnetism?

It is also called permanent magnet material, which refers to materials that are difficult to magnetize and difficult to demagnetize once magnetized. The basic requirement for this material is that the coercivity Hc is high, and the material with Hc>1000A/m is usually called a hard magnetic material.

The main use of hard magnetic materials is to make permanent magnets, so that a constant magnetic field is generated in a certain space. Compared with the current magnetic field, the magnetic field generated by it is stable in strength, does not require power, does not heat, and is small in size, so it is widely used in meters, telecommunications, electricity, transportation and daily necessities.

Three important permanent magnet materials commonly used are:

(1) Rare earth permanent magnet materials:

This is the current largest magnetic energy product of a large class of permanent magnet materials, rare earth group elements and iron group elements as the main component of metal intercompounds (also known as intermetallic compounds). Ndfeb rare earth alloy permanent magnet material developed and produced in China

(2) Metal permanent magnet materials:

This is a large class of development and application of iron and iron group elements (such as nickel, cobalt, etc.) as an important component of alloy-type permanent magnet materials, mainly aluminum nickel cobalt (AlNiCo) series and iron chromium cobalt (FeCrCo) series two categories of permanent magnet alloys.

(3) Ferrite permanent magnet material:

This is a composite oxide strong magnetic material (narrow sense) and magnetic ordered materials such as antiferromagnetic materials (broad sense) with Fe2O3 as the main component. It is characterized by high resistivity and is particularly beneficial in high-frequency and microwave applications. Such as barium ferrite (BaFe12O19) and strontium ferrite (SrFe12O19) have many applications.

Good soft magnetic materials should have these basic requirements:

(1) In order to improve functional efficiency, the initial permeability and maximum permeability should be high.

(2) In order to save resources, facilitate thin and short, quickly respond to the reversal of the polarity of the external magnetic field, the residual magnetic flux density should be low, and the saturation magnetic induction intensity should be high.

(3) Low loss, improve functional efficiency.

(4) Small coercive force, improve high-frequency magnetic properties.

(5) High resistivity, improve high frequency performance, reduce eddy current loss.

(6) Low magnetostrictive coefficient, reduce noise.

(7) As a basic characteristic, the magnetic anisotropy coefficient K is low, and it is easy to magnetize in each crystallization direction.

Hysteresis loops of soft magnetic(a) and hard magnetic(b) materials

Hysteresis loops of soft magnetic(a)and hard magnetic(b) materials

The difference between soft magnetism and hard magnetism:

At present, the most common ferrite magnet is hard magnetic ferrite, also known as permanent magnet ferrite. So what's the difference between them?

  • Materials with intrinsic coercive force greater than 0.8kA/m are called permanent magnet materials (hard magnetic), and materials with intrinsic coercive force less than 0.8kA/m are called soft magnetic materials.

  • The magnetic material is demagnetized according to the difficulty of magnetization. Hard magnetic materials have large remanence, high anisotropy field, high coercivity, large hysteresis loop area, and large magnetic field required for technical magnetization to saturation. Due to the high coercivity of hard magnetic materials, after being magnetized to saturation by technology and removing the magnetic field, it still maintains strong magnetism for a long time. Hard magnetic is suitable for permanent magnet; 

  • Soft magnetic materials have low coercivity, technical magnetization to saturation and remove the external magnetic field, it is easy to demagnetize, large permeability, suitable for electromagnet transformers and so on.

  •  Permanent magnet materials include aluminum-nickel-cobalt permanent magnet alloy, fe-chromium-cobalt permanent magnet alloy, permanent magnet ferrite, rare earth permanent magnet material and composite permanent magnet material.

  •  Soft magnetic materials mainly include metal soft magnetic materials, ferrite soft magnetic materials and other soft magnetic materials. The most widely used soft magnetic materials are iron-silicon alloy (silicon steel sheet) and various soft magnetic ferrites.

  • Soft magnetic ferrites are widely used in power and electronic engineering because of their high permeability and low coercivity. They are used in devices such as transformers, induction coils, inductors, high-frequency transformers and magnetic sensors. Hard magnetic ferrites Because of their persistent stable magnetic state, hard magnetic ferrites are mainly used to manufacture permanent magnets. These magnets are commonly found in magnetic recording media, electric motors, generators, electric vehicles, and various magnetic sensors.

Many people will ask will soft magnet replace permanent magnet? I don't think it will completely replace, because the development trend of the two kind material is different. 

However, it has been proved that at high frequency and ultra-high frequency, soft magnetic composites can replace part of the ferrite market, which is also beneficial for global development. High-frequency applications are prone to high consumption, if the use of low consumption to replace the high consumption, which is undoubtedly progress for the global energy conservation and control of environmental pollution.

In short, the development of soft magnetic materials will develop along the direction of high saturation magnetic induction intensity, high permeability, high Curie temperature, low loss, low coercivity and high frequency, miniaturization and thin shape. This also means that soft magnetic ferrite materials will be further developed towards high frequency, high permeability and low loss. The amorphous and nanocrystalline soft magnetic alloys will develop new and functional amorphous nanocrystalline composites and broaden the application field of amorphous nanocrystalline composites.

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