HRE-Free Neodymium Magnets

Additionally, there are concerns about losing control over proprietary specifications and end-user information. Since HRE-free Neodymium magnets fall outside the export control list, they have regained attention as a viable alternative.

Based on atomic number and properties, REEs are divided into 2 or 3 subgroups. In a 3-subgroup system, La, Ce, Pr, and Nd are light rare earths; Sm, Eu, and Gd are medium rare earths; and Tb, Dy, Ho, Er, Tm, Yb, and Lu are heavy rare earths. In a 2-subgroup system, La to Eu (7 elements) are light rare earths (LREEs), and Gd to Lu (7 elements) are heavy rare earths (HREEs). LREEs are generally more abundant and easier to extract from common deposits, while HREEs are rarer and more expensive to extract than LREEs.

The necessary intrinsic magnetic properties for any permanent magnet are a high Curie temperature (T_c), high saturation magnetization (M_s), and high anisotropy field (H_A). H_A is the primary source of intrinsic coercivity in rare earth magnets, as it determines how strongly the magnetic moments are aligned along preferred crystallographic directions.

The Nd₂Fe₁₄B compound stands out by combining high M_s with sufficient T_c and H_A, enabling exceptional energy density and practical advantages like cost-effectiveness and processability. This has allowed Neodymium magnets to commercialize widely and revolutionize industries since the 1980s.

In practical applications, coercivity is pivotal, as it governs the magnet’s resistance to demagnetization from external fields or heat, and thus its thermal stability—directly influencing application potential in high-stress environments.

Compounds like Tb₂Fe₁₄B and Dy₂Fe₁₄B exhibit low M_s but exceptionally high H_A, making them ideal for boosting coercivity. By partially replacing Nd with Dy or Tb in the Nd₂Fe₁₄B lattice, H_A increases, which elevates coercivity while maintaining acceptable M_s. This substitution strengthens the magnetocrystalline anisotropy, stabilizing domains against thermal fluctuations and demagnetizing fields.

HREEs are not essential for all Neodymium magnets but are added to enhance intrinsic coercivity. Without HREEs, standard Neodymium magnets can lose magnetism under heat or strong opposing fields, limiting their use in high-performance scenarios. HREEs are integrated during the manufacturing process of Neodymium magnets.

The earliest alloying process involves adding a certain proportion of Dy and Tb to the raw materials, then through melting to homogenize all elements, forming (HRE, Nd)₂Fe₁₄B phase with high magnetocrystalline anisotropy field to achieve coercivity improvement. However, as heavy rare earths are critical materials prone to supply chain disruptions and price volatility, Neodymium magnets produced this way face increased costs and raw material challenges. Additionally, due to antiferromagnetic coupling between heavy rare earth elements and Fe, remanence and maximum energy product are significantly reduced.

Therefore, reducing heavy rare earth usage while ensuring Neodymium magnets obtain high coercivity has been a focus for industry and academia, leading to processes like HRE-less (HRE-lean) and HRE-free Neodymium magnets.

Grain boundary doping technology mixes HREE-containing dopants with the original magnetic powder during the powder preparation process. The core of grain boundary doping is not changing the main phase structure of the magnet; heavy rare earth elements diffuse from grain boundaries into main phase grains during sintering, forming a magnetic hardening layer in the boundary region, optimizing grain boundary phase and interface structure, enhancing demagnetization decoupling effect, thus improving coercivity.

Grain boundary diffusion (GBD) process performs heavy rare earth elements diffusion on sintered Neodymium magnet blanks. At diffusion temperature, heavy rare earth elements diffuse along grain boundaries into the magnet, replacing part of Nd at grain boundaries and forming (HRE, Nd)₂Fe₁₄B core-shell structure around main phase grains, with HREE attaching to grain corner regions, enhancing the anisotropy field of the main phase, making demagnetization decoupling more pronounced. The most notable feature of GBD process is increasing coercivity while maintaining high remanence, and it has become the mainstream process.

Through equipment upgrades and process advancements in composition design, powder preparation, and sintering, some high-coercivity grades have already achieved HRE-free status. However, the rapid development and advantages of GBD technology have weakened the demand for these grain refinement approaches.

In recent years, most magnetic properties charts for Neodymium magnets have focused on illustrating advancements in GBD technology and high-abundance rare earth magnets. These charts typically highlight which grades can be produced using GBD processes, high-abundance rare earth compositions, or their combination—reflecting the rapid development and outstanding practicality of these technologies in enhancing coercivity, reducing material costs, and improving overall performance.

However, without China’s 2025 export restrictions on rare earth materials, it’s unlikely that updated versions of these charts would have emerged to specifically emphasize HRE-free capabilities. Manufacturers and users might not have prioritized noticing or selecting HRE-free options, as the focus remained on GBD and high-abundance innovations. The current situation has prompted the creation of this chart, which repurposes this progression to showcase export-ready HRE-free grades alongside traditional ones, aiding informed decisions in a restricted market.

It should be noted that HRE-free Neodymium magnets exhibit room-temperature magnetic properties comparable to those containing HREEs, with strong performance at normal temperatures. Despite this, they may have somewhat lower high-temperature magnetic properties, potentially weaker resistance to high-temperature demagnetization, and slightly poorer thermal stability. Therefore, reliability testing is essential before implementing substitutions.