This article is about the basic knowledge about special magnetic materials.
In addition to common soft magnetic materials and permanent magnet materials, there are a large number of varieties of other magnetic materials used in daily life. They play an important role in special fields with their different performances and characteristics. It is impossible to enumerate each of them because there are so many types. A few familiar examples will be introduced in this article.
When the external field changes, both the length and volume of the magnetic material will change slightly. The phenomenon is called magnetostriction. The change in length is called linear magnetostriction, and the change in volume is called volume magnetostriction. Volume magnetostriction is much weaker than linear magnetostriction, and magnetostriction usually refers to linear magnetostriction.
Magnetic materials will expand and contract with different magnetization states, and they will vibrate mechanically if they are magnetized with an alternating magnetic field. In this way, electromagnetic energy is converted into mechanical energy. This property has been used to produce various energy conversion devices, such as ultrasonic generators, sensors, etc. For common magnetic materials, the magnetostriction coefficient is small with only 0-30ppm. However, in recent years, it has been found that some materials made of rare-earth and iron have great magnetostriction coefficients that reach more than 1000ppm. Therefore, they are called large magnetostrictive materials or giant magnetostrictive materials.
As the name implies, magnetic plastics are plastic products with magnetism.
Ordinary plastics are not ferromagnetic. However, ferromagnetic materials can be formed by using special methods: one is to change the composition of plastics to make them magnetic. This method is still being researched. The second method is to add the magnetic powder to ordinary plastics to make them become composite magnetic plastics. The magnetic plastic manufactured in this way has been widely used in our daily life, which includes injection molding ferrite, injection molding neodymium iron boron, injection molding samarium iron nitrogen, and injection molding samarium cobalt magnets. The amount of injection molding ferrite is the largest.
In general, the ferromagnetic objects we see are solid. However, the magnetic liquid can be made by using artificial methods. The magnetic liquid (also called magnetic fluid) is actually made by a special method of mixing magnetic powder and a certain liquid. They have certain special application values because they are ferromagnetic and liquid.