A Brief Discussion on the Stability of Bulk Neodymium Magnets

When we talk about bulk neodymium magnets, we often first focus on "visible" performance indicators such as residual magnetic flux density (Br), coercivity (Hc), and (BH)max. However, with the wide application of bulk neodymium magnets in fields requiring long service life—such as aerospace, electric vehicles, and high-power wind turbines—designers are paying increasing attention to the stability of bulk neodymium magnets. It is thus evident that the performance stability of bulk neodymium magnets is also a crucial reference indicator.

During the long-term operation or storage of bulk neodymium magnets, their performance is not constant. Factors in the surrounding environment, such as temperature, humidity, and corrosive media, can all cause changes in the magnet's internal physical structure and chemical state, which in turn induce the attenuation of its magnetic properties.

Although the magnetic domains in most regions of a bulk neodymium magnets have been arranged orderly in a specific direction after magnetization, there still exist a small number of "reverse magnetic domains" with disordered magnetization directions inside. When subjected to the continuous action of external environmental factors, these existing reverse magnetic domains will continuously expand their scope, and new reverse magnetic domains will also be continuously generated. This process of magnetic domain disorder at the microscopic level directly leads to the degradation of the performance of bulk neodymium magnets materials.

Once this process occurs, it is irreversible: it will directly reduce the core performance indicators of the magnet, including residual magnetic flux density (residual magnetism), coercivity (demagnetization resistance), and maximum energy product (magnetic energy density). In severe cases, it may even cause the magnet to completely lose its magnetic function. Even if the bulk neodymium magnets material is remagnetized subsequently, its performance cannot be restored to the initial level before use, and this loss of magnetic performance is permanent.

The chemical properties of bulk neodymium magnets—with neodymium and iron (their main components) being active metals—determine their extremely poor resistance to environmental erosion. They are highly prone to oxidation and corrosion in conventional operating or storage environments such as humid conditions, acidic/alkaline surroundings, and high temperatures. This, in turn, leads to the attenuation of magnetic properties, structural damage, and even functional failure.

In practical applications, to maintain the temporal stability of bulk neodymium magnets, we can construct a dense, stable protective layer on the surface of bulk neodymium magnets materials (such as Ni-Cu-Ni electroplating, epoxy resin powder coating, zinc-aluminum coating, gold electroplating, or titanium nitride coating). This physically isolates the bulk neodymium magnets from contact with water, oxygen, and corrosive ions, blocking the electrochemical corrosion reaction at its source. As a result, the bulk neodymium magnets can operate long-term in environments like humid, high-humidity, or slightly corrosive conditions, with its service life extended from "several months (for untreated magnets)" to "several years or even more than a decade (for treated ones)".

In addition, the stability of bulk neodymium magnets is also related to their maximum operating temperature. According to the application, selecting an NdFeB permanent magnet with a suitable grade can also maintain the magnet’s stability in the application. The figure below shows some application scenarios matched with grades, which is for reference only.

In practical selection, it is necessary to first clarify the "maximum operating temperature" of the application scenario, then match the grade corresponding to the temperature class, and at the same time take into account both the requirement for magnetic energy product and cost factors. It is crucial to avoid focusing solely on "high magnetic energy product" while ignoring high-temperature stability, as this will lead to premature failure of the magnet.

If you have any doubts regarding the selection of permanent magnet grades and their applications (e.g., uncertainty about the suitable magnetic energy product, temperature class, corrosion resistance requirements, etc.), there is no need to repeatedly compare parameters on your own—we recommend consulting the sales engineers of Saint Langma first.

In addition, we Saint Langma can provide support for sample testing, suggestions for cost optimization, and technical details related to subsequent production adaptation (such as magnet dimensional tolerances and magnetization direction requirements). This helps you avoid "insufficient performance caused by improper selection" or "cost waste due to over-selection," so that make the selection process more efficient and accurate.

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