Ferrite magnet neodymium magnet for magnetic couplings

A Neodymium Magnet 

A neodymium magnet(also known as NdFeB, NIB or Neo magnet) is the most widely used type of rare-earth magnet. It is a Permanent Magnet made from an  alloy of neodymium,iron and and boron to form the Nd2Fe14B tetragonal crystalline structure.Developed independently in 1984 by General Motors and Sumitomo Special Metals,neodymium magnets are the strongest type of permanent magnet available commercially.

NdFeB magnets can be classified as sintered or bonded, depending on the manufacturing process used.They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as eletric motors in cordless tools, hard disk drives and magnetic fasteners.

Neodymium magnets are graded according to their maximum energy product, which relates to the magnetic flux output per unit volume. Higher values indicate stronger magnets. For sintered NdFeB magnets, there is a widely recognized international classification. Their values range from 28 up to 52. The first letter N before the values is short for neodymium, meaning sintered NdFeB magnets. Letters following the values indicate intrinsic coercivity and maximum operating temperatures (positively correlated with the Curie temperature ), which range from default (up to 80 °C or 176 °F) to TH (230 °C or 446 °F).

Anisotropic Ferrite Magnet

The Anisotropic Ferrite Magnets have a preferred direction of magnetisation within the structure and have strongest magnetic properties along that direction (they are more powerful than Isotropic Ferrite Magnets). There are two chemical varieties of ferrite magnet.

characteristic 

The powder metallurgy method has low remanence and low recovery magnetic permeability. High coercivity, strong anti-demagnetization ability, especially suitable for dynamic working conditions of magnetic circuit structure. Hard and brittle material, can be used for emery tools for cutting processing. The main raw material is oxide, so it is not easily corroded. Operating temperature :-40℃ to +200℃. 

Ferrite magnets are divided into anisotropic (heterotropic) and isotropic (isotropic). The magnetic properties of the isotropic sintered ferrite materials are weak, but they can be magnetized in different directions of the magnet. Heteromorphic sintered ferrite permanent magnet materials have strong magnetic properties, but only along the intended direction of magnetization of the magnet. 

Physical property 

In the actual production of ferrite magnets, raw materials with good chemical composition may not be able to obtain ferrite magnets with good properties and microstructure sometimes, because of the influence of physical properties. The listed physical properties of iron oxide include mean particle size APS, specific surface area SSA, and loose density BD. As iron oxide accounts for about 70% in the formula of manganese zinc ferrite magnet, its APS value has a great influence on the APS value of ferrite magnet powder. Generally speaking, the APS value of iron oxide is small, and the APS value of ferrite magnet powder is also small, which is conducive to speeding up the speed of chemical reaction. However, the APS value should not be too small considering that the fine particle of powder is not conducive to post-process pressing and sintering easy crystallization. Obviously, when the APS value of iron oxide is too large, only the diffusion reaction of spinel phase can be carried out in the pre-firing process due to the large particle size, and the grain growth process can not be further carried out. This inevitably leads to the increase of activation energy required during sintering, which is not conducive to solid phase reaction.