Share
SmCo 1:5 vs SmCo 2:17: Differences Between the Two Grade Families
In the field of industrial permanent magnets, Samarium Cobalt (SmCo) magnets hold a prominent position. Thanks to their high thermal stability, corrosion resistance, and reliable magnetic performance even under extreme operating conditions, they represent a key solution for numerous industrial applications. For a comprehensive overview of the characteristics, properties, advantages, and main applications of this technology, it is useful to start with our complete guide to Samarium Cobalt (SmCo) magnets. When moving to the design stage, however, the choice is mainly divided between two major grade families: SmCo 1:5 and SmCo 2:17.
Understanding the difference between these two Samarium Cobalt grades is essential for optimizing the thermal, magnetic, and economic performance of an application.
What Are Samarium Cobalt Magnets?
Samarium Cobalt magnets are intermetallic compounds consisting, as their name suggests, of the rare-earth element Samarium (Sm) and the transition metal Cobalt (Co). They belong to the category of sintered rare-earth magnets, together with the more widely used Neodymium magnets (NdFeB).
However, compared with Neodymium, Samarium Cobalt grades offer two key competitive advantages:
- Thermal stability: They can operate at temperatures well above 200°C, reaching 350°C or 400°C in some cases.
- Resistance to corrosion and oxidation: They often do not require galvanic or epoxy protective coatings, reducing post-processing costs and the risk of delamination.
These characteristics make them essential in the aerospace, defense, motorsport automotive, industrial sensing, and marine sectors.
Samarium Cobalt magnets are divided into two distinct metallurgical generations: the 1:5 series and the 2:17 series.
The SmCo 1:5 Family
The SmCo 1:5 series (often chemically designated as SmCo₅) represents the first generation of this technology, developed in the late 1960s.
The alloy consists of approximately 36% Samarium by weight and the remaining 64% Cobalt. Its crystal structure is hexagonal. This relatively simple elemental composition gives the magnet highly stable properties, but with less potential in terms of overall energy density.
Grades belonging to the SmCo 1:5 family are characterized by a maximum energy product, expressed as BHmax, generally ranging from 15 to 22 MGOe (MegaGauss-Oersted). This energy level is supported by a remanence (Br) typically ranging from 0.8 to 0.95 Tesla, equivalent to 8,000–9,500 Gauss, and good intrinsic coercivity (Hcj). The latter makes these magnets resistant to demagnetization caused by opposing external magnetic fields. In terms of thermal behavior, the maximum operating temperature is around 250°C, beyond which irreversible losses of magnetic flux can occur.
Among the advantages, ease of magnetization certainly stands out. These materials require a lower external magnetic field than the 2:17 series to reach full saturation, with typical values ranging from 20 to 30 kOe.
This is accompanied by good chemical stability, as the intrinsic composition of the alloy minimizes the risk of internal corrosion.
However, there are also some important limitations. The raw material cost is higher due to the high percentage of Samarium and the complete dependence on Cobalt, given the absence of less expensive metals such as Iron, making this alloy more exposed to fluctuations in raw material prices. Finally, its lower overall energy density must be considered, meaning that, for the same volume, SmCo 1:5 generates a lower magnetic field than its 2:17 counterpart.
The SmCo 2:17 Family
The SmCo 2:17 series (general chemical formula Sm₂Co,Fe,Cu,Zr₁₇) represents the second generation, introduced to overcome the power and cost limitations of the 1:5 series.
Unlike the previous formula, the crystal structure is rhombohedral and the alloy is more complex. Samarium accounts for approximately 25% of the weight. Cobalt is partially replaced by other metals:
- Iron (Fe): Added to increase remanent magnetization (Br) and reduce raw material costs.
- Copper (Cu): Fundamental to the domain-wall “pinning” mechanism, improving coercivity.
- Zirconium (Zr) or Hafnium (Hf): Added in small percentages to stabilize the crystalline phases during heat treatment.
The transition to the SmCo 2:17 family represents a significant technological evolution, expressed by an increase in the maximum energy product, BHmax, which typically falls within a range of 22 to 32 MGOe. This performance increase is reflected in a remanence (Br) capable of exceeding 1.15 Tesla (11,500 Gauss) and flexible intrinsic coercivity (Hcj). This value can be accurately adjusted during production by balancing the alloying elements, allowing customized high-coercivity grades to be produced.
The real strength of this second generation, however, lies in its thermal performance, with a maximum operating temperature normally ranging from 300°C to 350°C, but which can reach 400°C or 500°C in specially engineered grades.
The advantages of adopting SmCo 2:17 are directly related to these physical properties. Its high energy density provides a significantly better performance-to-volume ratio, a crucial factor that facilitates component miniaturization in projects where space is limited.
This is combined with exceptional flux stability even in the presence of significant temperature fluctuations, thanks to its low remanence temperature coefficient. Equally important is the economic factor: the introduction of Iron and the simultaneous reduction in the percentage of Samarium help mitigate the impact of rare-earth material costs on the finished product.
On the other hand, the metallurgical complexity of the 2:17 series also introduces specific limitations, starting with greater difficulty in magnetization. The rhombohedral structure requires extremely high magnetizing pulses for saturation, forcing manufacturers to use dedicated, high-power industrial equipment.
Finally, the coexistence of multiple metallurgical phases increases the material’s mechanical brittleness. This tendency to chip makes SmCo 2:17 more delicate to handle and limits subsequent machining to processes such as diamond grinding or electrical discharge machining (EDM).
Difference Between SmCo Grades: A Direct Comparison
To best support the selection of the most suitable Samarium Cobalt grade for an industrial project, it is useful to analyze the main differences between the two families.
Energy Density and Magnetic Strength
The difference in pure performance is significant. The structure of SmCo 2:17 allows Iron atoms to be incorporated into the crystal lattice, increasing the saturation magnetization. As a result, an SmCo 2:17 magnet can provide up to 50% more magnetic energy than an SmCo 1:5 magnet of the same size.
Thermal Behavior
Although both materials perform exceptionally well compared with Neodymium, SmCo 2:17 has the advantage when it comes to high-temperature applications. The Curie temperature—the temperature at which the material completely loses its magnetic properties—of SmCo 1:5 is approximately 750°C, while that of SmCo 2:17 exceeds 800°C. This translates into a maximum operating temperature of approximately 250°C for the former and up to 350°C–400°C for the latter.
Magnetization During Production and Assembly
A practical aspect that is often underestimated by designers concerns in-situ or post-assembly magnetization. SmCo 1:5 responds well to moderate magnetizing fields. If the magnet must be installed inside a rotor or complex sensor and then magnetized, the 1:5 series is considerably easier to manage.
SmCo 2:17 requires high-intensity magnetic pulses. If a company’s magnetizing equipment is not correctly sized, there is a risk of obtaining a partially magnetized magnet, resulting in reduced performance.
Not sure which SmCo grade to choose for your application?
The choice between SmCo 1:5 and SmCo 2:17 depends on several factors, including operating temperature, required energy density, available space, magnetization conditions, and design constraints. A preliminary technical assessment makes it possible to identify the most suitable grade and avoid either over-engineering or insufficient performance.
Contact our team to discuss your application requirements and identify the SmCo solution best suited to your project.
Guide to Choosing the Right Samarium Cobalt Grade
Choosing the ideal Samarium Cobalt grade does not follow a fixed rule, but depends on a balance of technical requirements. Here is a practical guide to help you make the right choice during the product design phase.
When Should You Choose SmCo 1:5?
The 1:5 option, although based on an older technology, still maintains unique application niches. It is recommended when:
- Available magnetizing fields are limited: If the application requires the magnet to be assembled in its demagnetized state and subsequently magnetized inside a closed magnetic circuit that is difficult to access.
- Chemical stability is the absolute priority: In chemically aggressive or marine environments where coating is not possible, the stability of the pure 1:5 crystal structure provides greater guarantees of long-term durability.
- The application operates strictly below 250°C: If the operating temperature does not exceed this threshold and exceptionally high magnetic induction is not required.
When Should You Choose SmCo 2:17?
The 2:17 series is the modern standard for most high-performance applications. It is the preferred choice when:
- Space is limited (Miniaturization): In high-performance brushless electric motors, aerospace systems, or military actuators where every millimeter and every gram matters.
- Temperatures exceed 250°C: For applications near combustion chambers, automotive exhaust systems, or deep geothermal drilling (downhole applications).
- The best magnetic performance-to-cost ratio is required: For the same generated magnetic flux, the lower Samarium content and higher energy density make 2:17 more cost-effective in high-volume production.
Both families are highly brittle. They should never be used as structural elements subjected to bending stresses or direct impacts. The design should always incorporate appropriate mechanical retention or bonding systems.
Identifying the correct grade at an early stage helps avoid costly over-sizing or, conversely, dangerous performance losses in the field.
Do you need to precisely define the magnetic specifications for your high-temperature application?
Contact us for personalized technical consulting, request samples, or obtain a targeted quotation for your industrial supply requirements.
