What are the differences between Sm1Co5 and Sm2Co17 magnets

junio 2, 2026

There are two options of magnet which are commonly used in high-temperature motors or the aerospace manufacturing: Sm1Co5 and Sm2Co17. Both of them are samarium-cobalt magnet (SmCo), which is a type of rare-earth magnet. The number in the name represented the atomic ratio between samarium (Sm) and cobalt (Co). For an engineer who is choosing a suitable magnet for a motor or aerospace components, it is essential to understand the difference between the two types of magnet.

Sm1Co5 represents a 1:5 samarium-to-cobalt ratio, which is the older type, while Sm2Co17 represents a 2:17 ratio, which is the newer,more commonly used type.

Compared with the commonly seen Nd FeB magnet, the magnetic force of the SmCo magnet is weaker. However, the heat resistance and corrosion resistance of the SmCo magnet is better than those of the Nd FeB magnet, making it a reliable choice in high-temperature or corrosive environments. Although the price of the SmCo magnet is higher, it is irreplaceable in high-end applications such as aerospace, medical equipment, and defense applications. The demand of SmCo magnets continues to grow because of the electric vehicle motor, drone, and precision instruments.

1. What is an Sm1Co5 magnet?

Sm1Co5 was discovered in the 1960s, which is the earliest samarium-cobalt magnet discovered. It contains only samarium and cobalt. Its energy product is at a medium level, which is 16-25 MGOe, and the maximum working temperature is 250 °C. It is rust-resistant because it does not contain any iron, no protective layer is required. The iron-free property is important in the ocean or chemical industry because it can reduce the cost of surface processing even in a corrosive environment. The energy product of 16–25 MGOe is sufficient for general industrial application.

It is also suitable for small batch orders or sampling as it can be easily processed to thin-walled, small rings, or other components with complex shape, and it is commonly seen in marine equipment, chemical pump, and other instruments operating in a vacuum environment.

Although the machining cost is lower, the material cost is higher than that of the Sm2Co17 magnet because of the higher cobalt content. That is the reason why the Sm1Co5 magnet is being replaced in the market, but it is still essential in specific applications.

2. What is an Sm2Co17 magnet?

Sm2Co17 is the newer type and is commonly seen in today’s market. Besides samarium and cobalt, it also contains small amounts of copper, iron, and zirconium . Its energy product is strong, which is 22–32 MGOe, and the maximum working temperature is 350°C. Because of the iron-containing property, it may rust in moisture environment, and the addition of a protective layer is recommended.

The addition of small amounts of copper,iron, and zirconium can improve magnetic force output and thermal stability, which is the reason why it is a default option in most industry and engineering, replacing the dominant position of Sm1Co5 magnet.

The temperature coefficient of the Sm2Co17 magnet is lower than that of the Sm1Co5 magnet. It indicates that the drop in magnetic force output is less when the working temperature increases. It is essential in the application with a large fluctuation in working temperature, such as the sensors embedded in aircraft engines.

Its strong magnetic force output and high maximum heat resistance make it widely used in electric vehicle motor, satellite components, and industrial robot.

3. Advantages and disadvantages of Sm1Co5 magnets

The feature of Sm1Co5 magnets is “replacing machining with magnetic force”. The sacrifice of magnetic force output in exchange for better machining flexibility and corrosion resistance.

Ventajas	Desventajas
Rust resistance	Weak energy product and magnetic force
Easy to calibrate the magnetic fields	Maximum working temperature is 250°C only
Easy to machine into complicated shape	Higher cost because of the higher composition of cobalt

Despite the weak magnetic force, its iron-free property is more important in some industries, such as medical equipment.

Its coercivity property also make it performs better in applications requiring precise magnetic field control, such as Magnetic Resonance Imaging (MRI) scanner and particle accelerator.

4. Advantages and disadvantages of Sm2Co17 magnets

The feature of Sm2Co17 magnets is reversed with Sm1Co5 magnets. The magnetic force output and the maximum heat resistance is the first priority, and the cost is processing difficulty and sensitivity to humidity.

Ventajas	Desventajas
Strong energy product and magnetic force	A protective layer is required in moisture environment
Maximum working temperature can reach 350°C	More difficult to machine or shape because of its fragile nature
Lower Temperature Coefficient (More stable in magnetic force when the working temperature changes)

The addition of one layer of NiCuNi (Nickel-Copper-Nickel) protective layer is sufficient to reduce rusting in most cases, and therefore, the increase in cost is limited.

Although it is fragile in nature, the use of diamond cutting tools and slow grinding can effectively reduce the risk of corner-chipping.

5. How to choose between Sm1Co5 and Sm2Co17 magnets?

There is no superior one between two types of magnet. The key concern is the requirement and the application environment.

Condition	The choice
Require stronger magnetic force	Sm2Co17
Working temperature higher than 250°C	Sm2Co17
Moisture environment and not going to add a protective layer	Sm1Co5
Require complicated shape/thinner wall	Sm1Co5
Limited budget	Sm2Co17

If it is hard to choose the type of magnet, it is recommended to consider Sm2Co17 first because of its better performance, lower price, and wider application. Sm1Co5 is considered only when the addition of a protective layer is not possible on corrosive environment or when a complex shape is required.

Although the unit price of Sm2Co17 magnet is lower, the overall cost will be higher if a protective layer is required, and the cost differences between the two will be narrowed. It is worthy to ask for a quote comparison from the supplier if the batch size is large.

If it is still indecisive after the above concern, the most reliable way is to contact the supplier, and provide the working temperature, environmental condition, and the size of the component. The supplier can recommend a choice according to the three parameters.

6. How to distinguish between Sm1Co5 and Sm2Co17 magnets?

● Label on package: the grade marking is usually printed on the label on the package, such as SmCo5 or SmCo26 (the most common grade of Sm2Co17). In case of label missing, a request of Material Certificate can be raised to the supplier.

● Pull-force test (for the same size): the higher magnetic force of Sm2Co17 makes it stronger in the test. The difference is visible to the naked eye.

● Rust test: slight rust spots may appear on Sm2Co17 in a moisture environment for 48-72 hours, but not on Sm1Co5

● Machinability: the fragile nature of Sm2Co17 makes it more prone to being corner chipped during cutting, and therefore the cutting speed had to slow down

If the magnet is purchased from secondhand markets or unknown suppliers, the above methods are useful. There are some unreliable suppliers who pass off Sm1Co5 magnet as Sm2Co17 magnet, as the appearance of these two magnets are the same. In case of a large purchase amount, it is recommended to ask for a third-party testing report, such as X-ray Fluorescence (XRF) analysis and magnetic properties testing, to ensure the correct type of magnet is received.