NdFeB vs SmCo Magnets: Complete Comparison Guide for Engineers

Overview: Two Families of Rare Earth Magnets

Both NdFeB and SmCo are rare earth permanent magnets — the strongest class of commercial magnets available. However, they differ significantly in composition, performance characteristics, and optimal use cases.

NdFeB (Neodymium Iron Boron, Nd₂Fe₁₄B) was developed in the 1980s and dominates the market due to its superior energy product and lower cost.

SmCo (Samarium Cobalt) was developed in the 1970s and remains the preferred choice for extreme environments where temperature and corrosion resistance outweigh cost considerations.

Head-to-Head Comparison

Property	NdFeB	SmCo
Maximum energy product (BH)max	52 MGOe (N52)	32 MGOe (SmCo 2:17)
Remanence (Br)	1.0–1.45 T	0.85–1.15 T
Coercivity (Hcj)	12–30 kOe	15–30 kOe
Max operating temperature	80–230°C (grade dependent)	250–350°C
Curie temperature	310–340°C	700–800°C
Temperature coefficient of Br	-0.11 to -0.13 %/°C	-0.03 to -0.04 %/°C
Corrosion resistance	Poor (requires coating)	Excellent (often used bare)
Mechanical strength	Brittle	Brittle (slightly more so)
Density	7.4–7.6 g/cm³	8.2–8.5 g/cm³
Relative cost	1× (baseline)	5–10× higher

Temperature Performance: The Critical Differentiator

Temperature stability is the single most important factor in choosing between NdFeB and SmCo.

NdFeB Temperature Classes

Grade suffix	Max operating temp	Typical applications
N (Standard)	80°C	Consumer electronics, speakers
M	100°C	General industrial
H	120°C	Automotive sensors
SH	150°C	EV motors, servo motors
UH	180°C	Aerospace actuators
EH	200°C	Downhole tools
AH	230°C	Extreme industrial

SmCo Temperature Classes

Series	Max operating temp	Typical applications
SmCo5	250°C	High-temp sensors
Sm2Co17	300–350°C	Turbine generators, military

Key insight: NdFeB grades above SH (150°C) require heavy rare earth additions (Dy, Tb), which significantly increase cost — narrowing the price gap with SmCo. Above 200°C, SmCo often becomes more cost-effective.

Corrosion Resistance

NdFeB contains iron, making it inherently susceptible to oxidation. Without coating, NdFeB magnets will corrode rapidly in humid environments. Standard coatings include:

NiCuNi (most common, 200+ hours salt spray)
Zinc (cost-effective, 48–96 hours salt spray)
Epoxy (500+ hours salt spray)
Parylene (excellent for medical/aerospace)

SmCo has inherent corrosion resistance and is often used without any surface coating. This makes SmCo the preferred choice for:

Marine and subsea environments
Chemical processing equipment
Medical implants (where coating integrity is critical)
Long-lifetime applications where coating degradation is a concern

Cost Analysis

NdFeB is significantly cheaper than SmCo on a per-kilogram basis. However, the total cost comparison depends on several factors:

Factor	NdFeB advantage	SmCo advantage
Raw material cost	✅ 5–10× cheaper	—
Coating cost	—	✅ Often no coating needed
High-temp grades	—	✅ Cheaper above 200°C
Machining	✅ Slightly easier	—
Long-term reliability	—	✅ No coating degradation
Size for same flux	✅ Smaller volume needed	—

Rule of thumb: For applications below 150°C in non-corrosive environments, NdFeB is almost always the better value. Above 200°C or in harsh environments, SmCo should be seriously evaluated.

Application Decision Matrix

Use NdFeB When:

Operating temperature is below 150°C
Maximum magnetic strength per volume is critical
Cost is a primary concern
Coating is acceptable (or environment is benign)
Applications: EV motors, wind turbines, consumer electronics, MRI machines, speakers, sensors

Use SmCo When:

Operating temperature exceeds 200°C
Corrosion resistance is critical (no coating desired)
Temperature coefficient must be minimal (precision sensors)
Long-term stability is more important than initial cost
Applications: aerospace actuators, military systems, downhole drilling tools, high-temp sensors, marine equipment

Consider Either When:

Operating temperature is 150–200°C (compare high-temp NdFeB vs. SmCo cost)
Application requires moderate corrosion resistance (evaluate coated NdFeB vs. bare SmCo)

Demagnetization Risk

Both magnet types can be demagnetized by:

Exceeding maximum operating temperature
Exposure to opposing magnetic fields exceeding the coercivity
Physical shock (more of a concern with SmCo due to higher brittleness)

NdFeB has a lower Curie temperature (310–340°C vs. 700–800°C for SmCo), meaning it loses magnetism more readily at elevated temperatures. For applications with thermal cycling or temperature spikes, SmCo provides a much larger safety margin.

Sourcing Considerations

Factor	NdFeB	SmCo
Global supply	90%+ from China	70%+ from China
Lead time	2–3 weeks (standard)	3–5 weeks
MOQ	100–500 pcs typical	200–500 pcs typical
Grade availability	Wide range stocked	More limited, often made to order
Raw material volatility	Nd price fluctuates	Co and Sm prices more stable

Frequently Asked Questions

Can I replace SmCo with a high-temp NdFeB grade?

In many cases, yes. Grades like N42SH (150°C) or N35UH (180°C) can replace SmCo in applications where the temperature allows. However, carefully evaluate the temperature coefficient — SmCo maintains flux much more consistently across temperature ranges.

Which is stronger?

NdFeB has a higher maximum energy product (52 MGOe vs. 32 MGOe), so for the same volume, NdFeB produces a stronger magnetic field. However, "stronger" depends on the application — if you need stable performance at 300°C, SmCo is effectively "stronger" because NdFeB would be demagnetized at that temperature.

Which is better for motors?

For most motor applications below 150°C (including EV motors), NdFeB is preferred due to higher energy product and lower cost. For motors operating above 200°C (e.g., aerospace or industrial), SmCo is the standard choice.

Need help selecting between NdFeB and SmCo for your application? Send us your operating conditions and we'll recommend the optimal material with a detailed technical rationale.