NdFeB Sintered Magnets: Manufacturing Process, Grades, and Performance

Guide - 26 Jul , 2026

NdFeB Sintered Magnets: Manufacturing Process, Grades, and Performance

In today’s technology landscape, NdFeB sintered magnets (Neodymium-Iron-Boron) are at the core of modern energy-efficient systems. Also known as neodymium magnets, these advanced rare-earth permanent magnets deliver the highest magnetic performance currently available on the market. From electric vehicle traction motors and wind power generation to microelectronics and industrial robotics, demand for these high-performance magnetic components continues to grow.

This article explores the complete journey of NdFeB sintered magnets, from raw materials to the finished product, examining the manufacturing process, grade classification system, and the latest technological innovations shaping the industry.

The manufacturing process is only one of the factors that determine the performance of permanent magnets. To learn more about their physical properties, grade classifications, and main industrial applications, read our guide Neodymium (NdFeB) Magnets: Properties, Grades, and Industrial Applications.

What is a Sintered NdFeB Magnet

Developed in the early 1980s, NdFeB magnets are based on the tetragonal crystal structure Nd2Fe14B. This specific atomic configuration gives the material an extremely high uniaxial magnetic anisotropy and a high saturation magnetization.

The term sintered NdFeB magnets refers to the main production method, hot sintering of powders, which differs significantly from the production of bonded magnets, which use plastic resins but offer lower magnetic properties. Sintering allows the highest possible material density to be achieved, unlocking unparalleled energy performance.

The NdFeB Production Process: From Melting to the Finished Product

The NdFeB production process is a high-precision metallurgical chain, where each individual stage drastically influences the final magnetic properties of the product. Strict control of the atmosphere (absence of oxygen) is essential, as pure neodymium is highly reactive and tends to oxidize.

Phase 1: Melting and Strip Casting

The process begins with the preparation of the alloy (Neodymium, Iron, and Boron, often enriched with small percentages of other metals such as Dysprosium, Terbium, Cobalt, Copper, and Aluminum) inside a vacuum induction furnace or under an inert gas atmosphere (Argon).

The molten alloy is then cast using Strip Casting technology: the liquid metal is poured onto a rotating copper drum cooled by water. This ultra-rapid cooling prevents the segregation of free iron and produces thin flakes with an extremely homogeneous crystalline microstructure.

Phase 2: Hydrogen Decrepitation (HD)

The flakes obtained from strip casting are extremely brittle. To reduce them into powder without introducing excessive mechanical stress or oxygen contamination, the hydrogen decrepitation process is used. The material is exposed to hydrogen gas, which penetrates the alloy grain. The crystal lattice expands, causing the material to undergo micro-fracturing, reducing it to a coarse powder.

Phase 3: Jet Milling

The coarse powder is introduced into a jet mill (Jet Mill), where high-pressure nitrogen jets cause the particles to collide with each other. This self-fracturing process reduces the particle size to an average diameter between 3 and 5 microns. The size is critical: each particle should ideally contain a single magnetic domain.

Phase 4: Magnetic Alignment and Pressing

The fine powder is introduced into a mold. At this point, a powerful external magnetic field is applied to align the magnetic domains of the individual particles along a single direction (magnetization axis). While keeping the field active, the powder is mechanically pressed (uniaxial and isostatic pressing) to form a “green body” (a compact but still fragile block). The alignment is what makes the magnet anisotropic, ensuring significantly higher performance compared to isotropic magnets.

Phase 5: Neodymium Sintering

The pressed blocks are placed into sintering furnaces at high temperatures (usually between 1050°C and 1150°C). During this crucial phase, the powder particles bond together at the atomic level, eliminating porosity and reducing the volume of the block by approximately 3-4%. The result is a solid metallic body with a density close to the theoretical value. Sintering is followed by an aging heat treatment at lower temperatures (approximately 600°C – 900°C) to optimize the grain boundary structure and maximize coercivity.

Phase 6: Mechanical Processing and Cutting

The sintered blocks have rough tolerances and simple geometric shapes (blocks, cylinders). After sintering, the block is mechanically processed until the required dimensions and tolerances are achieved.

Phase 7: Surface Treatment (Coating)

Sintered NdFeB magnets, due to the presence of iron, can oxidize.

To protect them, advanced surface coatings are applied such as:

  • Nickel-Copper-Nickel (Ni-Cu-Ni): The industrial standard for general-purpose use.
  • Epoxy Resin: Resistance to humidity and salt spray, electrically insulating.
  • Zinc Plating (Zn): An economical solution for environments that are not excessively aggressive.
  • Chemical Passivation: Used in aerospace or special applications.
  • Gold or Teflon Plating: Used in medical applications or clean rooms to ensure biocompatibility or the absolute absence of particulate release.

Magnetization and Quality Control


Finally, the machined and coated magnets are subjected to a high-intensity electromagnetic field to permanently saturate the magnetic domains. This is followed by quality control tests: magnetic flux measurement, accelerated aging tests (HAST / PCT), salt spray tests, and dimensional inspections.

At our production facility Cibas Sintered Magnets, we have developed an Integrated Quality System directly within the production line, designed to eliminate defects through three levels of automated scanning and testing:

  • Visual Inspection: We use advanced CCD technology machines (optical scanning cameras) for surface inspection. This system detects in real time micro-cracks, chipping, or coating defects invisible to the naked eye, ensuring the structural integrity of 100% of the magnets.
  • Weight Control: Each magnet passes through a highly precise Weight Class Control Machine. This step ensures that the density and mass of the component remain perfectly within the strict design tolerances, a crucial factor for rotor balancing in electric motors.
  • Advanced Magnetic Testing: The compliance of magnetic performance is verified through in-line testing systems. We use equipment with triaxial coils (Triaxial Coil) and in-line Triaxial systems, which allow measurement not only of the flux intensity but also of the exact magnetic orientation angle in 3D space, eliminating any magnetization deviation.

Thanks to this control ecosystem, Cibas Sintered Magnets guarantees stable, reliable industrial supplies that perfectly comply with the specifications of the required sintered NdFeB grades.

Sintered NdFeB Grades and Magnetic Performance

In the industrial market, not all magnets are the same. The classification of sintered NdFeB grades follows an international standard nomenclature that immediately identifies two fundamental parameters: the Maximum Energy Product BHmax and the Temperature Resistance (Intrinsic Coercivity Hcj).

A typical grade is identified by a code such as: N45SH.

  • The letter “N” stands for Neodymium.
  • The number “45” represents the maximum energy product expressed in MGOe (MegaGaussOersted). The higher this number, the greater the attractive force and the flux generated by the magnet.
  • The final letters (M, H, SH, UH, EH, AH) indicate the coercivity class, meaning the magnet’s ability to resist thermal demagnetization and opposing magnetic fields.

If a magnet exceeds its maximum operating temperature, it experiences a loss of magnetic flux that can be partially reversible or completely irreversible (permanent demagnetization), compromising the operation of the device in which it is integrated.

Need to choose the most suitable NdFeB grade for your project?

Each application requires a different balance between magnetic strength, high-temperature resistance, surface protection, and costs. An unsuitable choice can compromise product performance, reliability, and service life.

Contact our technicians to receive consultation in selecting the NdFeB magnet best suited to your project requirements. We will help you identify the most efficient solution based on operating conditions and your project objectives.

The Technological Revolution: Grain Boundary Diffusion (GBD)

How can the need to increase the coercivity of neodymium magnets be addressed without compromising the intensity of the magnetic field? The most important technological answer of recent years is called Grain Boundary Diffusion (GBD).

The Operating Principle of GBD
In traditional magnets, Dysprosium is melted together with all the other elements, distributing itself uniformly throughout the entire crystalline grain. However, the demagnetization of a magnet always begins at the weakest points, namely on the external surface of the crystalline grain and not inside it. Placing Dysprosium at the center of the grain is, from a magnetic point of view, a “waste” of valuable material, which also has the side effect of lowering the overall magnetic remanence (Br) of the magnet.

GBD technology reverses this paradigm through a process performed after sintering:

  • An NdFeB magnet is initially produced using only light rare earth elements (Neodymium/Praseodymium), thereby maximizing its magnetic remanence value (Br).
  • A thin layer of Dysprosium (Dy) or Terbium (Tb)-based compounds is applied to the surface of the machined magnet, in the form of powder, paste, or through physical vapor deposition (PVD).
  • The magnet is then subjected to a specific heat treatment at temperatures lower than the sintering temperature.
  • By exploiting the capillarity of the liquid phase formed at high temperatures, Dy or Tb atoms selectively diffuse inward, moving exclusively along the grain boundary channels and surrounding the Neodymium-Iron-Boron cores.

Since the core of the crystalline grain remains free of Dy/Tb, the magnet maintains an exceptionally high saturation magnetization. GBD allows a significant increase in coercivity (Hcj) while keeping remanence (Br) almost unchanged. It is possible, for example, to produce a grade with the magnetic strength of an N52 but with the thermal resistance of an UH or EH grade.

The Geopolitical Challenge of Heavy Rare Earths (HRE)

For decades, the only metallurgical method known to increase the coercivity of NdFeB magnets (allowing them to achieve SH, UH, EH, or AH grades without losing excessive magnetic remanence) was the alloying of Heavy Rare Earths (HRE – Heavy Rare Earths), specifically Dysprosium (Dy) and Terbium (Tb). By partially replacing Neodymium with Dysprosium in the primary alloy, the thermal stability of the magnet increases dramatically.

However, this solution currently presents major critical issues related to three main factors:

  1. Geopolitical Monopoly: More than 70% of global rare earth extraction and more than 90% of the refining capacity and production of sintered magnets are concentrated in a single country: China. In particular, heavy rare earths (Dy and Tb) mainly come from ion-adsorption clay deposits located in southern China and Myanmar, areas subject to strong geopolitical tensions and export restrictions.
  2. Scarcity and Costs: Dysprosium and Terbium are extremely rarer and more expensive elements compared to Neodymium and Praseodymium (LRE – Light Rare Earths). Their prices fluctuate significantly, making economic planning unstable for major automotive manufacturers or wind turbine producers.

In this critical context, new HRE-Free technologies (or technologies with very low HRE content) have been developed to ensure supply chain security and reduce costs without sacrificing performance.

Today, HRE-Free technological solutions are divided into two main configurations, capable of covering application requirements up to the advanced REN45SH grade:

  1. Pure HRE-Free: Magnets completely free of Dysprosium, Terbium, Gadolinium, and Holmium.
  2. Ho/Gd Version: Magnets that include Gadolinium and/or Holmium but completely eliminate the critical Terbium and Dysprosium.

However, it should be noted that reducing or eliminating heavy rare earths does not automatically result in a linear cost reduction. To compensate for the absence of Terbium and Dysprosium and maintain high performance levels, it is often necessary to integrate other elements into the alloy that, in turn, have significant market costs.

In conclusion, sintered NdFeB magnets remain one of the irreplaceable pillars of modern technology. However, the evolution of the global market is no longer driven solely by magnetic flux strength, but also by the resilience of the supply chain.

Does your project require the use of high-performance permanent magnets?

Contact us, together we will find the most suitable solution for your requirements.