NEWS

Magnetic materials are mainly divided into two major categories:
The first type is permanent magnet material (also known as hard magnetic material): the material itself has the characteristic of retaining magnetism.
The second type is soft magnetic material (also known as an electromagnet): it requires an external power source to generate magnetism.

The magnets we usually talk about generally refer to permanent magnetic materials.
Permanent magnet materials can also be broadly classified into two categories:
The first major category is: alloy permanent magnet materials, including rare-earth permanent magnet materials (neodymium-iron-boron Nd2Fe14B), samarium-cobalt (SmCo), and neodymium-nickel-cobalt (NdNiCo).
The second major category is ferrite permanent magnet materials, which, depending on the manufacturing process, are divided into sintered ferrites.
(Sintered Ferrite), Bonded Ferrite (Rubber Magnet), Injection-Molded Ferrite
(Zhusu Ferrite)—these three processes are further divided into isotropic and anisotropic magnets, depending on the orientation of the magnetic crystals.
These are currently the major permanent magnet materials available on the market. Others have been phased out due to limitations in production processes or high costs, making them unsuitable for widespread application—for example, Cu-Ni-Fe (copper-nickel-iron), Fe-Co-Mo (iron-cobalt-molybdenum), Fe-Co-V (iron-cobalt-vanadium), MnBi (manganese-bismuth), and AlMnC (cobalt-manganese-carbon).

Rare-earth permanent magnet material neodymium-iron-boron (Nd2Fe14B) is divided into three types:

Sintered neodymium-iron-boron: High coercivity, high magnetic performance, can be machined into various shapes, but is prone to rusting and requires surface treatment.

Bonded neodymium iron boron: One-step molding, no secondary processing required; uniform magnetism, corrosion resistance, and excellent temperature stability.

Injection-molded neodymium iron boron: High precision, capable of producing thin-walled rings or magnets with complex shapes.

Sintered Ferrite:

The primary raw materials are BaFe12O19 and SrFe12O19, and the magnets are classified into isotropic and anisotropic types.

Low price, moderate magnetic properties, good temperature resistance, and wide range of applications.

Rubber Magnet:

Made by compounding bonded ferrite powder with synthetic rubber, it features softness and elasticity.

It can be processed into various shapes and used in industries such as refrigerators, advertising, and toys.

Aluminum-Nickel-Cobalt (AlNiCo):

Made up of metallic elements such as aluminum, nickel, and cobalt, it is divided into two types: sintered and cast.

The casting process can produce parts of various sizes and shapes, while the sintering process is limited in terms of size but offers excellent machinability.

High operating temperature, suitable for use in instruments and meters, among other fields.

Samarium cobalt (SmCo):

They are divided into SmCo5 and Sm2Co17, representing the first- and second-generation rare-earth permanent magnet materials. These materials are scarce and expensive, yet they boast high magnetic energy products and excellent temperature characteristics, making them particularly suitable for high-temperature operating environments.

The History of Magnets:
With the development of society, the applications of magnets are becoming increasingly widespread—from high-tech products to the simplest packaging magnets. Currently, neodymium-iron-boron (NdFeB) permanent magnets and ferrite magnets remain the most widely used.

Looking at the historical development of permanent magnet materials, carbon steel—used in the late 19th century—had a maximum magnetic energy product (BH)max (a physical quantity measuring the density of magnetic energy stored in a permanent magnet) of less than 1 MGOe (megagauss-oersted). In contrast, today’s commercially produced Nd-Fe-B permanent magnet materials from overseas have achieved a magnetic energy product exceeding 50 MGOe. Over the past century, the remanence Br of these materials has improved only slightly; the significant increase in magnetic energy product is largely attributable to the enhancement of coercivity Hc. The improvement in coercivity, in turn, has been driven primarily by a deeper understanding of its underlying mechanisms, the discovery of compounds with high magnetic anisotropy, and advances in manufacturing technologies. At the beginning of the 20th century, carbon steel, tungsten steel, chromium steel, and cobalt steel were the primary materials used for making permanent magnets.

It was only with the successful development of AlNiCo permanent magnet materials in the late 1930s that the large-scale application of permanent magnets became feasible. In the 1950s, the emergence of barium ferrite not only reduced the cost of permanent magnets but also expanded their application range into the high-frequency domain. By the 1960s, the advent of rare-earth cobalt permanent magnets ushered in a new era for their applications. In 1967, Strnat and colleagues at Dayton University in the United States successfully produced SmCo5 permanent magnets using the powder bonding method, marking the dawn of the rare-earth permanent magnet era. To date, rare-earth permanent magnets have progressed from the first-generation SmCo5 and the second-generation precipitation-hardened Sm2Co17 to the third-generation Nd-Fe-B permanent magnet materials. In addition, alloys such as Cu-Ni-Fe, Fe-Co-Mo, Fe-Co-V, MnBi, and AlMnC have historically been used as permanent magnet materials. However, due to their relatively poor performance and high costs, these alloys are now rarely employed in most applications. On the other hand, alloys like AlNiCo, FeCrCo, and PtCo continue to find use in certain specialized applications. Currently, barium and strontium ferrites remain the most widely used permanent magnet materials; yet, many of their traditional applications are gradually being replaced by Nd-Fe-B-based materials. Moreover, today the output value of rare-earth permanent magnet materials has far surpassed that of ferrite permanent magnets, and the production of rare-earth permanent magnets has grown into a major industry.