Which Type of Magnet Do You Actually Need?

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Buyer's Guide

Magfine Technical Team March 2025 10 min read

Neodymium, ferrite, samarium cobalt — the options stack up fast. This guide cuts through the jargon and gives you a straight answer based on what your application actually demands.

Key Takeaways

Neodymium (NdFeB) is the strongest permanent magnet type available and covers the vast majority of industrial and commercial applications.
Ferrite is the right call when budget matters more than compactness, or when operating temperatures exceed 150°C.
Samarium cobalt (SmCo) earns its premium in high-temperature, corrosive, or aerospace environments where nothing else holds up.
Grade selection and coating are just as important as material choice — a correctly specified N42 with epoxy coating outperforms a mismatch in either direction.

We get some version of this question every week. An engineer sources a motor component and realizes the magnet spec is wrong. A product designer needs holding force but has almost no space. A procurement manager is staring at three quotes with three different materials and needs to decide by Friday.

The problem isn't a lack of information — it's too much of it, too scattered, and often written for engineers who already know the answer. This guide is for the person who doesn't yet. We'll cover the three main permanent magnet families, where each one is genuinely the right call, and the grade and coating decisions that follow once you've picked a material.

which type of permanent magnet?

The Three Families You'll Actually Choose Between

Permanent magnets — the kind you buy, install, and don't need to power — fall into a few material families. Three of them cover the vast majority of real applications.

Neodymium (NdFeB)

Neodymium magnets are the strongest permanent magnets commercially available. Made from an alloy of neodymium, iron, and boron, they pack more magnetic force per unit of volume than anything else in this category. When someone asks for "the strongest magnet," this is what they mean.

The tradeoff is temperature. Standard grades start losing meaningful magnetic strength above roughly 80°C, and without a protective coating they corrode. For most room-temperature industrial and consumer applications neither limitation matters. But in a motor running hot or a marine environment, you need to plan for both.

If your application runs at room temperature and you need the most force from the smallest package, neodymium is almost always the right starting point.

Ferrite (Ceramic)

Ferrite magnets — sometimes called ceramic magnets — are made primarily from iron oxide and barium or strontium carbonate. They're significantly weaker than neodymium per unit of volume, but they're dramatically cheaper, naturally corrosion-resistant, and they hold their performance well in heat.

This is the magnet used in refrigerator door seals, loudspeaker assemblies, small DC motors, and anywhere cost matters more than compactness. Ferrite still accounts for the majority of magnet volume shipped globally — not because it's glamorous, but because it's reliable and inexpensive.

Worth knowing

Ferrite magnets have an unusual characteristic: their magnetic performance actually improves slightly at lower temperatures. If your application runs cold, ferrite becomes more attractive relative to neodymium than room-temperature numbers suggest.

Samarium Cobalt (SmCo)

Samarium cobalt is the specialist. It offers magnetic strength close to neodymium — sometimes matching it grade for grade — combined with exceptional temperature resistance and corrosion resistance that requires no coating. That combination makes it irreplaceable in specific applications: aerospace actuators, downhole drilling tools, high-temperature motors, and military equipment.

What keeps SmCo out of everyday applications is cost. Cobalt is expensive and its pricing is volatile. You pay a significant premium over neodymium for those temperature and corrosion properties. For most applications that premium isn't justified. For the right application it's the only option that works.

Side-by-Side: What the Numbers Mean

The table below compares the three families on the dimensions that matter most for sourcing decisions.

Property	Neodymium (NdFeB)	Ferrite (Ceramic)	Samarium Cobalt (SmCo)
Magnetic strength	Very high Best in class	Low–moderate Weakest of three	Very high Near NdFeB
Max operating temp	80–200°C (grade-dependent) Grade selection critical	Up to 250°C Good inherently	Up to 350°C Best in class
Corrosion resistance	Poor — coating required Must specify coating	Excellent — no coating needed Inherently resistant	Excellent — no coating needed Inherently resistant
Relative cost	Moderate Mid-range	Low Most economical	High–very high Cobalt premium
Typical applications	EV motors, sensors, speakers, hard drives, holding magnets	Fridge seals, loudspeakers, small DC motors, low-cost assemblies	Aerospace, high-temp motors, military, downhole tools

Magnet size comarpsion

Picking a Grade: What the N-Number Means

If you've chosen neodymium, you'll encounter grade designations like N35, N42, N52, N35SH, N42UH. The number refers to the maximum energy product — a measure of the magnet's total magnetic energy density, expressed in megagauss-oersteds (MGOe). Higher number means stronger magnet.

The letter suffix indicates the maximum operating temperature before irreversible demagnetization begins:

Standard grades — N35 to N52

No letter suffix, or just "N"
Max operating temp: ~80°C
Best price-to-performance for room-temperature use
Consumer electronics, holding magnets, sensors

M and H grades

Max operating temp: 100–120°C
Modest cost premium over standard
Industrial motors, automotive components
Specify when ambient temp consistently exceeds 60°C

SH and UH grades

Max operating temp: 150–180°C
Higher cost, slightly reduced room-temp strength
EV traction motors, HVAC compressors, wind turbines
When heat is a primary design constraint

EH and AH grades

Max operating temp: up to 230°C
Highest cost within the NdFeB family
High-performance industrial motors, oil and gas
Niche — most applications don't require these

Practical rule of thumb

Start with a standard grade (N35–N42 covers most applications well). Move up in temperature rating only if you've confirmed your operating environment will consistently exceed 60°C. Over-specifying temperature grade adds cost without any benefit at lower temperatures.

Coatings: Don't Skip This Step for Neodymium

Raw neodymium is reactive. Without protection it oxidizes rapidly — within days in a humid environment, and within months even in dry air. Every neodymium magnet needs a coating. The question is which one.

Nickel-copper-nickel (Ni-Cu-Ni)

This is the standard. The bright silver finish on most catalog neodymium magnets. It provides solid corrosion resistance for indoor and moderate-humidity environments, has good adhesion, and doesn't significantly affect magnetic performance. If you don't have a specific reason to use something else, start here.

Epoxy

Epoxy adds chemical and impact resistance on top of the base nickel layer — the right call for applications involving harsh chemicals, lubricants, or solvents, and for outdoor or marine assemblies where moisture exposure is inevitable. The coating is thicker, which matters in tight-tolerance fits. Magfine's proprietary Hi-DEN HDC epoxy coating consistently clears 200 hours in ASTM B117 salt-spray testing, making it one of the most durable options available for Canadian industrial and outdoor conditions.

Zinc and tin

Zinc is used where a lower-cost alternative to nickel is acceptable and chemical resistance isn't a priority. Tin where solderability matters in electronics assembly work. Neither is a go-to for general industrial use.

Gold and parylene

Gold plating is used in medical devices and high-value electronic assemblies where biocompatibility or conductivity matters. Parylene — a conformal polymer coating applied by vapour deposition — is used in precision applications where the thinnest possible coating is needed without compromising protection.

Magnet coating comparison

The Decision, Simplified

These aren't rules — they're the right starting point for 80% of applications we see come through.

Need maximum force from minimum space at room temperature? Neodymium, N42, nickel-coated. That single specification covers more ground than any other.

Choose ferrite when: budget is the primary constraint, the assembly is large enough that size isn't an issue, operating temperature exceeds 150°C, or the environment is too harsh for coated neodymium and SmCo is overkill.

Choose samarium cobalt when: operating temperature exceeds 180°C, the environment is corrosive and a coating would fail, or the application is in aerospace, defence, or downhole drilling where the specification demands it.

Choose neodymium in every other case.

Frequently Asked Questions

What is the strongest type of magnet?

Neodymium (NdFeB) magnets are the strongest permanent magnets commercially available. The highest-grade neodymium magnets (N52) have an energy product roughly 10 times that of a standard ferrite magnet of the same size. For electromagnets — which require a continuous power source — field strengths can go far higher. But for permanent magnets you buy and install without a power supply, neodymium is the answer.

What's the difference between N35 and N52 neodymium magnets?

Both are neodymium magnets — the number refers to the maximum energy product (in MGOe), which correlates directly with magnetic strength. N52 is approximately 40% stronger than N35 at the same volume. N52 also costs more and is slightly more temperature-sensitive. For most applications N35 or N42 is sufficient. N52 is worth specifying when you've run out of space and need more force from the same footprint.

Can neodymium magnets be used outdoors?

Yes, but coating selection is critical. Standard nickel-copper-nickel coating is adequate for sheltered outdoor use or low-humidity environments. For direct exposure to rain, salt spray, or standing water, an epoxy coating is required. In marine or highly corrosive environments, samarium cobalt may be worth the cost premium to avoid coating failure. Magfine's Hi-DEN HDC epoxy coating was developed specifically for demanding Canadian outdoor and industrial conditions.

What magnet is best for electric motors?

It depends on operating temperature and performance requirements. Most EV traction motors and high-performance servo motors use high-temperature grade neodymium (SH, UH, or EH grades), which balances high magnetic density with adequate thermal stability. Budget DC motors — fan motors, small appliance motors — often use ferrite because performance requirements are lower. Aerospace and military motors with extreme temperature requirements use samarium cobalt.

How do I know what size magnet I need?

Magnet sizing comes down to the required pull force, the gap between the magnet and its target surface, and the target material. The closer the magnet is to the target and the larger the contact area, the more holding force. For critical applications we recommend a flux density calculation or FEA simulation. For general-purpose use, our application team can size magnets based on your required holding force and space constraints — contact us directly.

Are all neodymium magnets the same quality?

No, and this matters more than most buyers realize. Quality varies significantly by manufacturer — in actual versus rated performance, dimensional tolerances, coating adhesion, and batch-to-batch consistency. Reputable manufacturers provide material certificates and third-party testing data. If a supplier can't produce documentation, that's worth taking seriously. All Magfine products are RoHS and REACH compliant, with certificates available on request.

Not sure which magnet fits your application?

Our technical team has helped engineers and procurement teams spec magnets across industries for years. Send us your requirements and we'll give you a straight answer.

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