Types of Magnets: Permanent, Temporary & Electromagnets

The Three Core Types of Magnets You Need to Know

There are three fundamental types of magnets: permanent magnets, temporary magnets, and electromagnets. Of these, permanent magnets are by far the most widely used in everyday technology — from the speaker in your phone to the sensors inside a Magnetic Encoder on an industrial robot. Temporary magnets lose their magnetic properties once an external field is removed, while electromagnets rely on electric current to generate a field. Understanding these distinctions is not just academic; choosing the wrong magnet type can cause a motor to fail, a sensor to drift, or an encoder to produce inaccurate position data.

Permanent magnets are further divided into four main families based on material composition: neodymium iron boron (NdFeB), samarium cobalt (SmCo), alnico, and ceramic/ferrite. Each has a distinct energy product, temperature range, and coercivity — the resistance to being demagnetized. The table below gives an at-a-glance comparison of these four permanent magnet types:

Neodymium Magnets: The Strongest Permanent Magnets Available

Neodymium iron boron (NdFeB) magnets are the most powerful permanent magnets in commercial production today. With a maximum energy product reaching 52 MGOe, a single neodymium magnet the size of a thumb can exert forces that would be impossible to match with older magnet materials. They are graded from N35 to N52 — the number indicates the maximum energy product in megagauss-oersteds. An N52 magnet is not just slightly stronger than an N35; it contains roughly 49% more magnetic energy per unit volume.

The primary limitation of NdFeB magnets is temperature sensitivity. The remanence — residual magnetic flux — drops at a rate of approximately 0.12% per degree Celsius, meaning a magnet operating at 150°C loses roughly 15% of its room-temperature field strength. For applications above 150°C, samarium cobalt becomes the preferred alternative. Corrosion is the second major weakness: bare neodymium magnets oxidize quickly and must be coated with nickel, zinc, epoxy, or gold depending on the operating environment.

Despite these constraints, NdFeB magnets dominate in electric vehicle motors, wind turbine generators, MRI machines, hard disk drives, and miniaturized sensors. They are also the magnet of choice in many compact Magnetic Encoder assemblies where high field strength in a very small package is essential for achieving the resolution needed in precision motion control. A Magnetic Encoder reading angular position at 4,096 counts per revolution — a common specification in servo motor feedback — demands a magnet that delivers a stable, strong field over a very short sensing distance, and neodymium reliably meets that requirement.

Neodymium Magnet Grades and What the Numbers Mean

Grade designations for NdFeB magnets follow a straightforward convention. The "N" prefix denotes the standard neodymium material. Some grades include additional letter suffixes:

• N (no suffix) — standard grade, maximum operating temperature around 80°C
• M (medium) — maximum operating temperature around 100°C
• H (high) — maximum operating temperature around 120°C
• SH (super high) — maximum operating temperature around 150°C
• UH (ultra high) — maximum operating temperature around 180°C
• EH (extremely high) — maximum operating temperature around 200°C

When specifying a magnet for a Magnetic Encoder or motor application, both the energy product grade and the temperature suffix matter equally. A high-grade N52 magnet installed in an environment regularly reaching 140°C will demagnetize far faster than a lower-grade N42UH operating in the same conditions.

Samarium Cobalt Magnets: High Temperature and Extreme Environment Performance

Samarium cobalt (SmCo) magnets belong to the same rare-earth category as neodymium but solve a different set of problems. Their maximum operating temperature reaches 300°C, and their temperature coefficient of remanence is just -0.03% to -0.04% per degree Celsius — roughly three times more stable than NdFeB over temperature. For engineers designing aerospace actuators, downhole oil and gas sensors, or military-grade motor drives, this thermal stability is not optional; it is the primary selection criterion.

SmCo magnets are classified into two sub-families. The SmCo5 series (1:5 stoichiometry) delivers energy products in the range of 15–22 MGOe. The Sm2Co17 series (2:17 stoichiometry) reaches 22–30 MGOe with even better temperature resistance. Both are brittle and difficult to machine, making them more expensive to fabricate into precise shapes. However, their resistance to corrosion is significantly better than NdFeB — SmCo magnets can often operate without any protective coating, which matters in chemically aggressive environments.

In magnetic sensing applications, SmCo is the preferred material when a Magnetic Encoder or position sensor must operate reliably across wide temperature swings. A rotary encoder mounted on a spindle motor in a precision CNC machine may experience ambient temperatures from -10°C during overnight shutdown to over 100°C during heavy cutting operations. Over that 110°C range, a neodymium magnet's field might shift enough to introduce position errors, while a samarium cobalt magnet maintains essentially the same flux density.

Alnico Magnets: Excellent Temperature Stability but Low Coercivity

Alnico magnets — the name comes from aluminum, nickel, and cobalt — were the dominant high-performance magnet material from the 1940s through the 1960s. They can be used at temperatures up to 550°C, which is higher than any other conventional permanent magnet family. Their residual flux density (Br) is reasonably high, allowing them to produce significant field strengths in certain magnetic circuit configurations.

The critical weakness of alnico is its extremely low coercivity. Coercive field strength — the external magnetic field needed to demagnetize a magnet — is only around 640–1,900 A/m for alnico, compared to over 800,000 A/m for a typical neodymium magnet. This means alnico magnets demagnetize easily when exposed to opposing magnetic fields, impacts, or even improper storage. Traditional bar magnets and horseshoe magnets sold as teaching tools are typically alnico, which is why they come with a steel "keeper" to prevent demagnetization during storage.

Today, alnico magnets are primarily used in guitar pickups, microphones, loudspeakers, and analog measuring instruments — applications where the shape of the magnetic field matters more than raw field strength, and where the interaction between an instrument's magnet and an external field is part of the design. They are rarely used in modern Magnetic Encoder systems because the risk of demagnetization from nearby motor fields or electrical disturbances makes them unsuitable for precision feedback applications.

Ceramic and Ferrite Magnets: The Most Widely Used Magnets in the World

Ceramic magnets — also called ferrite magnets — are made from iron oxide (Fe2O3) combined with barium or strontium carbonate. They were first developed in the 1960s and remain the most widely produced magnet material by volume. The reason is straightforward: raw material costs are low, the manufacturing process (pressing and sintering) is scalable, and the resulting magnets are highly resistant to both corrosion and demagnetization. A ferrite magnet sitting in a damp outdoor environment for ten years will lose negligible magnetization compared to an uncoated neodymium magnet in the same conditions.

The trade-off is energy density. Ferrite magnets have an energy product of only 1–5 MGOe, roughly one-tenth that of neodymium. For any application requiring compact size and strong field, ceramic magnets are inadequate. They are also brittle and require diamond grinding when precision machining is needed. However, for large-format applications — electric motor stators in appliances, magnetic separation equipment, ferrite ring cores in power supplies, and automotive sensors — ferrite magnets provide more than sufficient performance at a fraction of the cost.

In magnetic encoder applications, ferrite multi-pole magnetic rings are widely used, particularly in encoder wheels for industrial servo drives where cost efficiency matters and the ring diameter is large enough to compensate for the lower energy density. A ferrite magnetic ring with 64 pole pairs on a 34mm diameter ring, for example, is a standard component in many motor feedback systems — large enough to deliver adequate field at the sensor surface while keeping per-unit cost low. These ferrite encoder rings typically operate across a temperature range of -20°C to 200°C, which suits most factory automation environments.

Flexible Ferrite Magnets and Their Use in Sensors

A specialized form of ferrite magnet mixes magnetic powder with a rubber or plastic binder to create a flexible sheet or strip magnet. These materials can be cut with scissors, wrapped around curved surfaces, and attached with adhesive backings. Flexible ferrite strips are used extensively in refrigerator seals, promotional magnets, and advertising signs. In technical applications, rubber ring magnets are a popular choice for certain Magnetic Encoder designs: they offer good impact resistance, stable pole orientation, and the ability to customize pole counts and track configurations. Their applicable temperature range is typically -20°C to 50°C, limiting them to moderate-temperature environments.

Electromagnets: Controllable Magnetic Fields on Demand

Electromagnets work on a fundamentally different principle from permanent magnets. A coil of wire wound around a ferromagnetic core — typically iron — produces a magnetic field whenever electrical current flows through it. Remove the current and the field disappears. This on-off controllability makes electromagnets indispensable in applications where a permanent magnetic field would be a problem: industrial lifting magnets that release steel parts on command, solenoid valves that open and close with a control signal, and MRI machines that require precise field control during imaging sequences.

The strength of an electromagnet scales with the number of coil turns and the current passing through them, measured in ampere-turns. A laboratory electromagnet generating 2 tesla might use 10,000 ampere-turns or more. Superconducting electromagnets, which use coils cooled to near absolute zero to eliminate electrical resistance, can reach fields above 45 tesla — far beyond any permanent magnet. These are the magnets used in particle accelerators, fusion research reactors, and research-grade NMR spectrometers.

In everyday industrial use, electromagnets power relays, contactors, brakes, and clutches. They also form the basis of variable-reluctance sensors — an older type of magnetic position sensor that detects the passage of ferrous gear teeth. Unlike a Hall-effect Magnetic Encoder, a variable-reluctance sensor requires no power supply; it generates its own voltage signal as the gear tooth passes through the magnetic field. This passive operation makes it attractive in safety-critical systems where sensor power loss would be catastrophic.

Temporary Magnets: How They Work and Where They Appear

Temporary magnets are materials that become magnetized only in the presence of an external magnetic field and return to a non-magnetic state when that field is removed. Common examples include soft iron, low-carbon steel, and certain nickel alloys. The physical mechanism is domain alignment: in an external field, the microscopic magnetic domains within the material rotate into alignment, creating a net magnetic moment. Remove the field, and thermal agitation randomizes the domains again within seconds or minutes.

The most familiar temporary magnets are ordinary steel paper clips, nails, and screwdrivers that become magnetized near a strong permanent magnet and then slowly lose that magnetism when moved away. In engineering, temporary magnetism is exploited in transformer cores, motor laminations, and relay armatures — materials that need to be magnetized and demagnetized rapidly without retaining residual flux, which would cause heating and energy loss.

The distinction between permanent and temporary magnetic behavior is formalized in the concept of magnetic "hardness." Hard magnetic materials (high coercivity) resist demagnetization and make good permanent magnets. Soft magnetic materials (low coercivity) magnetize and demagnetize easily and are used wherever the field needs to change rapidly. Silicon steel laminations used in transformer cores, for example, have coercivity as low as 8 A/m — making them extremely easy to magnetize and demagnetize at 50 or 60 Hz without significant hysteresis loss.

Natural Magnets: Lodestone and the History of Magnetic Discovery

The first magnets humans encountered were not man-made. Lodestone — a naturally magnetized variety of the mineral magnetite (Fe3O4) — occurs in deposits worldwide where geological processes have allowed magnetite crystals to cool slowly in the presence of Earth's magnetic field, locking in permanent magnetization. Ancient Greek and Chinese scholars observed lodestone attracting iron as early as 600 BC. The Chinese use of lodestone compasses for navigation is documented as early as 1086 AD, predating European compass use by at least a century.

Magnetite itself forms when iron-rich igneous rocks cool, and the magnetization of natural specimens typically measures in the range of a few hundred gauss — weak compared to modern engineered magnets but sufficient for compass alignment. Lightning strikes are one proposed mechanism for magnetizing surface magnetite deposits; the intense current pulse creates a brief but extremely strong local magnetic field that can permanently magnetize nearby iron oxide minerals.

Natural magnets have no practical engineering use today — their field strengths are too variable and too low. But their discovery was the starting point for the entire science of electromagnetism, which directly enables every modern permanent magnet, every electric motor, and every Magnetic Encoder or Hall-effect sensor in use today.

How Magnets Are Used in Magnetic Encoders and Position Sensing

A Magnetic Encoder is a sensor system that uses a permanent magnet — or an array of alternating magnetic poles — to detect rotational or linear position. The magnet creates a field that changes as the target moves; a sensor (typically a Hall-effect IC or a magnetoresistive element) reads those changes and converts them into electrical signals representing position, speed, or direction. The output may be incremental (a series of pulses proportional to movement) or absolute (a unique code for every position across the full range of travel).

The type of magnet selected for a Magnetic Encoder has direct consequences for performance. Five types of magnets are commonly applied to magnetic encoder systems:

• Rubber ring magnets — flexible bonded ferrite rings with good impact resistance and stable pole orientation; suitable for -20°C to 50°C environments; popular in standard encoder products with single and dual tracks
• Ferrite multi-pole magnetic rings — sintered ceramic rings used widely in industrial servo encoders; cost-effective and operable to 200°C but brittle and typically require a metal bracket for structural support
• Injection-molded ferrite magnets — complex shapes achievable with high dimensional accuracy; superior durability and impact resistance; preferred when encoder geometry is non-standard or when tight tolerances are required
• Neodymium ring or disc magnets — used in compact, high-resolution encoders where the sensing gap is small and maximum field strength is needed; common in miniaturized servo feedback systems
• Samarium cobalt magnets — selected when the encoder must operate at high temperatures or in corrosive environments that would degrade neodymium; typical in aerospace and downhole applications

The magnetization direction is equally important. Radially magnetized ring magnets create alternating north and south poles around the circumference, which is the standard configuration for rotary incremental encoders. Axially magnetized disc magnets — with north on one face and south on the other — are used in absolute single-turn encoders where a single rotating magnet above a Hall-effect chip provides full 360° position data with no additional hardware. Diametrically magnetized cylindrical magnets, magnetized across their diameter rather than along their axis, provide a sinusoidal field rotation that is ideal for high-accuracy interpolation algorithms in on-axis encoder ICs.

Compared to optical encoders, Magnetic Encoder systems tolerate contamination from dust, oil, and moisture far better. An optical encoder stops working the moment its glass disc or photodetector gets coated with machine coolant; a magnetic encoder continues operating because the magnetic field passes through non-ferromagnetic contamination without significant attenuation. This robustness explains why magnetic encoder technology dominates in heavy industry, construction equipment, agricultural machinery, and outdoor robotics — anywhere that a clean, controlled environment cannot be guaranteed.

Incremental vs Absolute Magnetic Encoder Configurations

Incremental magnetic encoders use a multipole ring with alternating N and S poles of equal width arranged around the circumference. As the ring rotates, the Hall sensor or magnetoresistive element detects each pole transition and outputs a pulse. Counting pulses gives relative displacement from a reference position. These encoders are simple, low-cost, and suitable for speed control and relative positioning tasks — motor commutation in BLDC drives, conveyor speed feedback, and printer carriage position are typical applications.

Absolute magnetic encoders encode a unique position value at every point in the range of travel, so the system knows its exact position even after a power cycle without needing to home. Single-turn absolute encoders typically use a diametrically magnetized two-pole magnet above an encoder IC containing multiple Hall elements arranged to read the rotating field angle. Multi-turn absolute encoders add a gear train with additional magnets and sensors to track how many full rotations have occurred, extending position memory across multiple revolutions. The magnet material in absolute encoder configurations is typically neodymium for high-resolution single-turn designs and ferrite for larger-diameter multi-turn gear magnets where cost is the primary constraint.

Key Properties That Determine Which Magnet to Use

Selecting a magnet for any application — from a simple door latch to a high-precision Magnetic Encoder — requires evaluating several interdependent properties rather than focusing on a single specification like "strongest available."

Remanence (Br)

Remanence is the residual magnetic flux density remaining in a magnet after it has been fully magnetized and the external magnetizing field removed. Measured in Tesla (or Gauss), it directly determines how strong the magnet's field will be in a working circuit. NdFeB magnets achieve Br values up to 1.45 T; ferrite magnets typically reach only 0.35–0.43 T. A higher Br means a stronger working field for a given magnet volume.

Coercivity (Hc)

Coercivity measures how resistant a magnet is to demagnetization by an external field. High coercivity means the magnet retains its field in the presence of opposing fields, mechanical shock, and elevated temperatures. NdFeB and SmCo magnets both have very high coercivity (typically 800,000–2,000,000 A/m), making them stable in the strong magnetic environments generated by motors and coils. Alnico's low coercivity (640–1,900 A/m) makes it unsuitable for most modern precision applications despite its excellent temperature stability.

Maximum Energy Product (BHmax)

BHmax is the single number that best characterizes overall magnet performance — it represents the maximum amount of magnetic energy that can be stored per unit volume. Higher BHmax means more force or field can be generated from a smaller magnet. This is why neodymium magnets enabled a generation of miniaturized motors, speakers, and sensors that simply were not possible with ferrite or alnico. When space is constrained, as it is in the compact housing of a servo motor feedback Magnetic Encoder, BHmax determines whether the design is physically achievable.

Temperature Coefficient

All permanent magnets lose some field strength as temperature rises. The temperature coefficient of Br expresses this as a percentage change per degree Celsius. NdFeB: approximately -0.12%/°C. SmCo: approximately -0.03%/°C to -0.04%/°C. Alnico: approximately -0.02%/°C. Ferrite: approximately -0.2%/°C (and notably, ferrite also has a positive temperature coefficient for coercivity, meaning it actually becomes harder to demagnetize at higher temperatures — the opposite of NdFeB). For sensor applications involving wide temperature ranges, these coefficients determine whether field variation across the operating range will introduce unacceptable measurement error.

Physical Form Factor and Magnetization Direction

Permanent magnets can be manufactured in virtually any shape: discs, rings, blocks, arcs, cylinders, and custom profiles. The magnetization direction — axial, radial, diametric, or multipole — is set during the sintering and magnetization process and cannot be changed afterward. For magnetic encoder applications, choosing the correct combination of physical shape and magnetization direction is as important as choosing the right material. A diametrically magnetized cylinder used as an on-axis encoder magnet must have its magnetization precisely aligned with its geometric axis; a deviation of even 1–2 degrees introduces harmonic errors in the position output that limit achievable accuracy.

Common Applications of Each Magnet Type Across Industries

Understanding where each magnet type excels in real applications helps clarify the selection logic that engineers follow. The following breakdown covers the most significant use cases:

Neodymium Magnet Applications

• Electric vehicle traction motors and regenerative braking systems
• Hard disk drive voice coil actuators and spindle motors
• Compact servo motor feedback using Magnetic Encoder on-axis sensing
• Consumer electronics speakers, microphones, and haptic actuators
• MRI machine gradient coil assemblies and high-field research equipment
• Wind turbine direct-drive generators (large ring magnets in the stator assembly)

Samarium Cobalt Applications

• Aerospace actuators and jet engine sensor systems operating above 150°C
• Military-grade motor drives and guidance system sensors
• High-temperature Magnetic Encoder assemblies in turbomachinery
• Downhole oil and gas drilling tools exposed to elevated pressure and temperature
• Precision laboratory instruments requiring long-term field stability

Ferrite/Ceramic Magnet Applications

• Household appliance motors (washing machines, refrigerator compressors, fans)
• Ferrite multi-pole rings in industrial servo encoder wheels
• Magnetic separation equipment for removing iron contaminants from food and mining products
• Loudspeaker drivers in cost-sensitive consumer audio products
• Automotive wheel speed sensors (ABS rings) and crankshaft position sensors

Alnico Magnet Applications

• Electric guitar pickups (PAF-style humbuckers and single-coil pickups use Alnico 2, 3, or 5)
• Dynamic microphone capsules
• Galvanometer movements and analog panel meters
• Electro-permanent magnetic chucks and lifting magnets
• High-temperature sensing applications where coercivity requirements are modest

Electromagnet Applications

• Industrial lifting magnets for scrap yards and steel processing facilities
• Solenoid valves, relays, and contactors in control systems
• MRI scanners (superconducting electromagnets achieving 1.5–3 T in clinical use)
• Maglev train levitation and propulsion systems
• Electromagnetic brakes and clutches in industrial machinery

Magnet Shapes and How Geometry Affects Performance

The shape of a permanent magnet has a large influence on its effective working field, even when the material grade is held constant. This is because the demagnetizing factor — the degree to which the magnet's own field opposes itself internally — depends on geometry. A long, thin magnet (like a bar magnet) has a lower demagnetizing factor than a flat disc; as a result, the bar magnet retains more of its theoretical Br in practice. Engineers account for this by designing the magnetic circuit — the arrangement of magnet, pole pieces, and air gaps — to maximize flux delivery to the working area while minimizing leakage.

Common magnet shapes and their typical applications include:

• Disc and cylinder magnets — used as on-axis sensing magnets in Magnetic Encoder systems, as well as in small motors, sensors, and fastener applications; available in both axial and diametric magnetization
• Ring magnets — used as multipole encoder rings, speaker assemblies, and motor rotor rings; the hollow geometry accommodates a shaft passing through the center, which is essential for through-bore encoder mounting
• Block/rectangular magnets — used in linear motors, magnetic couplings, holding systems, and laboratory experiments; straightforward to stack and arrange in arrays
• Arc or segment magnets — curved pieces that fit around a cylindrical rotor; used in brushless DC motor stators and generators where multiple arc magnets form a complete ring
• Pot magnets (cup magnets) — a disc magnet housed in a steel cup that concentrates flux to one surface; used in holding and clamping systems to multiply effective pull force by a factor of three to five compared to an unhoused magnet of the same grade

Caring for Magnets: Demagnetization Risks and Storage Best Practices

Even high-coercivity permanent magnets can lose their magnetization under the wrong conditions. The main demagnetization risks are heat, opposing magnetic fields, and mechanical shock — each acting through a different physical mechanism but all resulting in domain misalignment and reduced residual flux.

Temperature is the most predictable risk. Every magnet material has a Curie temperature — the point at which thermal energy overwhelms the exchange interaction holding magnetic domains aligned, and all magnetization is permanently lost. For neodymium, the Curie temperature is approximately 310–340°C. However, irreversible demagnetization begins well below the Curie point; NdFeB magnets may begin losing magnetization permanently at temperatures as low as 80°C in unfavorable magnetic circuit conditions. This is why operating temperature specifications for neodymium magnets must be respected in motor and encoder designs.

Opposing magnetic fields are a risk primarily during handling and assembly. Bringing a neodymium magnet close to a larger, stronger magnet in an opposing orientation can partially demagnetize it — a process called "working point displacement" on the B-H curve. For magnets used in precision applications like Magnetic Encoder rings, any partial demagnetization introduces asymmetries in the pole pattern that directly translate to position errors at the sensor output. Specialized magnetizing and assembly fixtures are used in professional encoder manufacturing to prevent this.

Practical storage and handling rules for permanent magnets include:

• Store magnets in pairs with opposite poles facing to reduce external stray fields and internal demagnetization
• Use steel "keepers" for alnico bar and horseshoe magnets to bridge the poles and minimize self-demagnetization
• Keep strong neodymium magnets away from electronics, pacemakers, credit cards, and mechanical watches at distances of at least 30–50 cm for larger grades
• Avoid dropping or hammering magnets; mechanical shock can randomize domain alignment in materials with marginal coercivity
• Do not expose uncoated NdFeB magnets to humidity; hydrogen from moisture accelerates oxidative degradation