How a Permanent Magnet Is Created: The Direct Answer

A permanent magnet is created by taking a ferromagnetic material — most commonly an alloy of neodymium, iron, and boron (NdFeB), or combinations of iron, aluminum, nickel, and cobalt (Alnico) — and exposing it to a powerful external magnetic field that aligns the material's internal magnetic domains in a single, fixed direction. Once that alignment is locked in through a combination of heat treatment, sintering, and magnetization, the material retains its magnetic field indefinitely without any external energy source. This is the defining characteristic that sets a permanent magnet apart from an electromagnet, which only produces a field when current flows through it.

The manufacturing process is far more involved than simply holding a piece of metal near another magnet. Industrial permanent magnets — including those used in Magnetic Encoder systems, electric motors, MRI machines, and wind turbines — go through a highly controlled sequence of alloying, powder preparation, pressing, sintering, machining, and final magnetization. Each step determines the strength, stability, and durability of the finished magnet.

The Physics Behind Permanent Magnetism

To understand how a permanent magnet is made, it helps to understand why certain materials can hold a magnetic field in the first place. Magnetism at the atomic level originates from the spin of electrons. In most elements, electrons exist in pairs that spin in opposite directions, canceling each other's magnetic effects. But in ferromagnetic materials — iron, nickel, cobalt, and their alloys — a number of unpaired electrons remain, and their spins can align in the same direction.

These groups of aligned atoms form regions called magnetic domains. In an unmagnetized piece of iron, the domains point in random directions, so the net magnetic effect is zero. When an external magnetic field is applied, the domains rotate to align with the field. In magnetically "soft" materials like pure iron, the domains revert to random orientations once the field is removed. In magnetically "hard" materials — the ones used to make permanent magnets — the domains stay aligned even after the external field is gone. This property is described by a material's coercivity, which is its resistance to demagnetization. The higher the coercivity, the more stable the permanent magnet.

Materials with a wide hysteresis loop, high coercivity, and high remanence (residual magnetization) are the candidates for permanent magnets. The engineering challenge is selecting and processing these materials so that coercivity is maximized and the domain alignment is locked in permanently.

Types of Permanent Magnet Materials and Their Composition

There are five major families of permanent magnet materials in commercial use today. Each has a different composition, manufacturing method, and performance profile.

Neodymium magnets dominate the market for high-performance applications because of their exceptional energy density. NdFeB magnets now account for over 25% of the total worldwide permanent magnet market and are found in everything from computer hard drives and electric vehicle motors to the compact permanent magnets used inside a Magnetic Encoder mounted on a motor shaft. Their chemical formula is Nd₂Fe₁₄B, and their energy product ranges from 26 to 52 MGOe depending on the grade and manufacturing precision.

Samarium cobalt magnets were discovered in the 1960s and became significant for miniaturization. Their high-temperature performance — remaining stable at temperatures exceeding 300°C — makes them preferred in aerospace and precision instrumentation where neodymium magnets would lose strength.

Alnico magnets, the first synthetic permanent magnets developed in the 1930s in Japan, remain in use for their extreme temperature tolerance and relatively high remanence, despite their low coercivity. Ferrite magnets are the most economical option and are still produced in very high volumes for everyday consumer products.

Step-by-Step: How Neodymium Permanent Magnets Are Made

The most widely used method for manufacturing high-performance permanent magnets is Powder Metallurgy, specifically a sintering process. Here is how it works in practice for NdFeB magnets, the type most commonly found in motors, generators, and Magnetic Encoder assemblies.

Stage 1: Raw Material Batching and Alloying

The process begins by weighing out precise quantities of neodymium, iron, and boron, along with small amounts of other elements like dysprosium or praseodymium that modify specific magnetic properties. These raw materials are loaded into a vacuum induction furnace and melted together at temperatures exceeding 1,600°C. The molten alloy must be protected from oxygen at all stages because the rare earth elements are highly reactive. Once fully melted and mixed into a homogeneous liquid, the alloy is cast — either poured into molds, spread onto a chill plate, or processed in a strip caster that produces a thin, continuous metal strip. The resulting solid material is a dense metallic alloy without any magnetic properties yet.

Stage 2: Pulverizing Into Fine Powder

The cast alloy is crushed using jaw crushers and then ground down using ball mills or jet mills into an extremely fine powder. The target particle size is typically 3 to 7 microns in diameter — roughly the size of a red blood cell. At this particle size, each grain ideally corresponds to a single magnetic domain, which is critical for achieving maximum alignment later in the process. This fine powder is chemically reactive and can ignite spontaneously in air, so the entire milling and handling process is carried out under an inert atmosphere of argon gas or in a vacuum.

Stage 3: Pressing and Domain Alignment

This is the stage where the future magnetic orientation of the finished magnet is established. The powder is placed into a die or a flexible container, and a strong external magnetic field — typically several Tesla — is applied just before or during compaction. This field forces the tiny particles to rotate and line up with their easy-magnetization axes all pointing in the same direction. The press then compacts the powder, "freezing" this alignment into a solid shape called a green compact.

There are two main pressing methods. In axial pressing, the aligning field runs parallel to the compaction direction. In isostatic pressing, the powder is sealed in a flexible container and placed in a fluid press where equal pressure is applied from all sides. Isostatic pressing allows blocks up to 100 × 100 × 250 mm to be produced with superior alignment, as the powder is not disrupted by the mechanical forces of the die walls. Higher alignment directly translates to a higher energy product in the finished magnet.

Stage 4: Sintering and Heat Treatment

The green compact is loaded into a vacuum sintering furnace and heated to a temperature just below the melting point of the alloy — typically around 1,050°C to 1,100°C for NdFeB. At this temperature, the powder particles fuse together through a process called liquid phase sintering, creating a dense, solid magnet body. After sintering, the material undergoes one or more aging heat treatments at lower temperatures (typically 450°C to 650°C) to optimize the microstructure and maximize coercivity. The entire sintering cycle takes place in a vacuum or inert gas atmosphere to prevent oxidation. The sintered NdFeB material at this point has a hardness of Rockwell C 57 to 61 — comparable to hardened tool steel — and is extremely brittle.

Stage 5: Machining Into Final Shape

Because sintered rare earth magnets are so hard and brittle, they cannot be machined with standard tools. All cutting, grinding, and shaping operations require diamond-plated wheels and blades. Slicing can be performed with high precision. Complex profiles and bore features are produced using EDM (electrical discharge machining). The small cylindrical permanent magnets used at the shaft end of a motor in a Magnetic Encoder system, for example, are ground to extremely tight dimensional tolerances — often ±0.05 mm or tighter — to ensure the sensor can detect the rotating magnetic field accurately and consistently.

Stage 6: Surface Coating and Corrosion Protection

NdFeB magnets are highly susceptible to corrosion. Without surface treatment, they degrade rapidly in humid or chemically aggressive environments. Standard coatings include nickel-copper-nickel (the most common), zinc, tin, silver, gold, epoxy resin spray, and phosphate treatment. The choice of coating depends on the operating environment. For Magnetic Encoder applications where the magnet is enclosed inside a motor housing or protected assembly, a standard nickel coating is typically sufficient. For outdoor or marine applications, epoxy or multi-layer nickel coatings provide greater protection.

Stage 7: Final Magnetization

At this point in manufacturing, the magnet body still has very little residual magnetic field — the domain alignment from pressing is present but the material has not been fully magnetized. Magnetization is done by placing the finished, coated part inside a magnetizing coil or fixture and discharging a very high-current pulse through the coil. A capacitor is first charged to high voltage (energy storage), then discharged through a coil with very low resistance. The peak current during discharge can reach tens of thousands of amperes, generating a magnetic field strong enough to saturate all the aligned domains simultaneously. The magnet emerges fully magnetized and must be handled carefully from this point on because it will attract ferrous objects and other magnets with significant force.

How Alnico Magnets Are Made: A Different Process

Alnico magnets follow a different manufacturing route. The primary elements — aluminum, nickel, cobalt, and iron — are melted together and cast into molds, a process that has not changed significantly since Alnico magnets were first developed in the 1920s. Casting produces coarse-grained alloys with the internal structure needed for high remanence. After casting, the parts are heat-treated in the presence of a magnetic field, which causes the alloy's microstructure to form elongated single-domain particles aligned with the applied field.

An alternative method is sintered Alnico, where the alloy is ground into powder, pressed, and sintered — similar to NdFeB manufacturing. Sintered Alnico has slightly lower magnetic performance than cast Alnico but allows for more complex shapes and tighter dimensional tolerances. Both types are then magnetized using a high-current pulse, just as with rare earth magnets.

The key practical limitation of Alnico magnets is their low coercivity — they demagnetize relatively easily when exposed to opposing fields or physical shock. This is why they have been largely replaced by rare earth magnets in precision applications like rotary magnetic encoder systems, where stable, consistent magnetic field output is critical for accurate angle detection.

The Role of the Permanent Magnet in a Magnetic Encoder

Understanding how a permanent magnet is created matters directly in the context of a Magnetic Encoder because the quality of the magnet — its field uniformity, temperature stability, and resistance to demagnetization — determines the accuracy and reliability of the position feedback the encoder provides.

A Magnetic Encoder is a sensing device that detects rotational position by measuring changes in a magnetic field. In its simplest configuration, it consists of just two components: a permanent magnet attached to the rotating shaft and a magnetic sensor (usually a Hall effect sensor or a magnetoresistive sensor) mounted on a fixed PCB. As the shaft and its attached magnet rotate, the direction of the magnetic field at the sensor's location changes continuously. The sensor converts this field variation into electrical signals, typically sinusoidal waveforms, which the signal processing circuit interprets as angular position, rotational speed, and direction.

Magnetization Direction and Encoder Accuracy

The permanent magnet used in a Magnetic Encoder can be magnetized in different directions, and this choice affects both accuracy and susceptibility to interference. A radially magnetized magnet creates a magnetic field that is parallel to the shaft's rotation axis. This configuration produces a large, uniform field in the area near the center of the rotation axis, making the system more tolerant of small positional misalignments between the magnet and the sensor — a condition called "misalignment." A plane-magnetized (axially magnetized) magnet reduces leakage fields that could interfere with nearby electronics, but it produces a narrower region of uniform field, making the system more sensitive to misalignment errors.

For most Magnetic Encoder designs, the ideal configuration is the shaft-end arrangement: the center of the rotating shaft, the permanent magnet, and the Hall element are all aligned on the same axis. When this geometry is achieved, the Hall sensors detect a sinusoidal variation in the horizontal field components as the magnet rotates. Two Hall sensors oriented 90° apart (measuring the Bx and By field components) provide a complete quadrature signal set from which the absolute angular position within one revolution can be calculated.

Material Selection for Encoder Magnets

Not all permanent magnet materials are equally suitable for Magnetic Encoder applications. The small cylindrical or disc-shaped magnets in a typical rotary encoder are almost always made from sintered or bonded NdFeB, sometimes with neodymium partially substituted by praseodymium or supplemented with dysprosium for improved temperature stability. The magnet must maintain a consistent, predictable field over the full operating temperature range of the encoder — commonly −40°C to +125°C in automotive and industrial applications. If the magnet's remanence changes significantly with temperature, the Hall sensor will measure different field strengths at the same angular position depending on ambient temperature, introducing systematic angular errors.

Modern magnetic encoders achieve resolutions of up to 16 bits per revolution, corresponding to an angular resolution of 0.0055°, rivaling the accuracy of optical encoders. Reaching this level of performance requires a permanent magnet with field uniformity and temperature stability that only high-grade sintered NdFeB or SmCo can provide. In harsh environments where an optical encoder's glass disk could shatter or its optical path could be contaminated by oil, dust, or moisture, a Magnetic Encoder with a robust rare-earth permanent magnet remains fully functional.

Incremental vs. Absolute Magnetic Encoders

Magnetic Encoder systems fall into two broad categories that differ in how their permanent magnet arrays are structured:

• Incremental encoders use a ring or disk with alternating north and south magnetic poles arranged around the circumference. As the disk rotates, the sensor reads the passing poles and counts pulses. The raster pitch (distance between pole pairs) determines resolution. Common pitches are 1 mm, 2 mm, and 5 mm. Through electronic interpolation, a ring with a 1 mm pitch can achieve measurement steps of 0.001 mm (1 µm). These encoders provide relative position — they need a reference point on startup.
• Absolute encoders use a more complex magnet arrangement — either a single multi-pole permanent magnet or a ring magnet with a coded pattern — so that every angular position has a unique magnetic signature. A permanent magnet mounted on the encoder shaft creates a distinct field at every angular position. The sensor reads this field and generates an absolute position value without needing to count from a reference. Some multi-turn absolute magnetic encoders use the Wiegand effect: a small Wiegand wire changes magnetic polarity abruptly each time the encoder shaft completes a half-revolution, generating a voltage pulse that powers the counting circuit even when the system is powered off.

In both cases, the performance of the Magnetic Encoder depends directly on the quality of the permanent magnet at its core — its field strength, uniformity, temperature coefficient, and long-term stability against demagnetization from vibration, shock, or stray fields.

What Makes a Permanent Magnet Lose Its Magnetism

Despite the name, permanent magnets are not truly permanent — they can and do lose magnetism under certain conditions. Understanding these failure modes is essential for anyone using permanent magnets in long-life applications like Magnetic Encoder systems embedded in motors or industrial equipment.

• Heat (exceeding the Curie temperature): Every ferromagnetic material has a Curie temperature above which thermal energy disrupts domain alignment and the material loses its magnetism. For NdFeB, the Curie temperature is about 312°C. Even below this temperature, elevated heat causes reversible and eventually irreversible losses in remanence. This is why encoder magnets must be matched to the operating temperature of the motor or shaft they are mounted on.
• Opposing magnetic fields: A magnetic field applied in the opposite direction to the magnet's polarization — if strong enough — can partially or fully demagnetize it. The coercivity value of the material determines how much opposing field it can withstand. High-coercivity grades of NdFeB are specifically designed for applications where stray fields from adjacent motor windings or other magnets could otherwise cause gradual demagnetization over time.
• Physical shock and vibration: Severe mechanical shock can disturb domain alignment in lower-coercivity materials like Alnico. This is one reason Alnico has largely given way to rare earth magnets in vibration-prone industrial environments.
• Corrosion: NdFeB magnets corrode if their protective coating is compromised. Corrosion progressively degrades the magnetic material itself, reducing field strength over time. Proper coating selection during manufacturing is therefore critical for long service life.

Bonded Magnets: An Alternative Manufacturing Route

Not all permanent magnets are made by sintering. Bonded magnets are produced by mixing magnetic powder — typically NdFeB, SmCo, or ferrite — with a polymer binder such as epoxy resin or nylon, then molding or extruding the mixture into shape. The process is simpler and cheaper than sintering and allows for very complex near-net shapes without machining. However, bonded magnets have lower magnetic performance than sintered magnets because the polymer binder dilutes the volume fraction of magnetic material.

Bonded NdFeB magnets are widely used in small motors, sensors, and — notably — in the ring magnets and multipole disks used in some Magnetic Encoder designs where a large number of precisely spaced pole pairs is more important than maximum field strength per unit volume. The ability to injection-mold bonded magnets with integrated multipole magnetization in a single step makes them cost-effective for high-volume encoder manufacturing.

The magnetization of bonded magnets follows the same general principle as sintered magnets — a high-current pulse through a coil generates a field that aligns and saturates the magnetic domains — but because the particles are smaller and partially constrained by the binder, the magnetizing field required is lower than for fully dense sintered material.

Practical Considerations When Selecting a Permanent Magnet for Encoder Applications

For engineers specifying a Magnetic Encoder system or designing a motion control assembly that incorporates one, the characteristics of the permanent magnet are not incidental — they are a primary design parameter. Several factors should be evaluated:

• Field strength and uniformity: The Hall sensor in a Magnetic Encoder operates most accurately when the field it detects is consistent and predictable as the magnet rotates. Variations in field strength due to poor manufacturing or irregular magnetization introduce angular errors. High-grade sintered NdFeB magnets with tight dimensional and magnetic tolerances minimize these errors.
• Temperature coefficient: NdFeB has a remanence temperature coefficient of approximately −0.11% per °C. SmCo has a lower coefficient of about −0.03% per °C, making it preferable in applications with wide temperature swings where angle accuracy must be maintained without electronic compensation.
• Magnetization direction: Radial magnetization (field pointing outward from the shaft axis) or diametric magnetization (field pointing across the diameter of a disc magnet) each produce different field distributions above the magnet face. The sensor IC datasheet typically specifies which magnetization direction is required for correct operation.
• Physical dimensions and tolerances: The magnet must be centered on the shaft to within the misalignment tolerance specified by the encoder IC manufacturer — commonly ±0.5 mm or better. The air gap between the magnet face and the sensor also affects the field strength at the sensing element and must be kept within a specified range.
• Stray field management: In densely packed motor and drive assemblies, the stray field from the encoder magnet can interfere with other magnetic components. Using a plane-magnetized magnet instead of a radially magnetized one can reduce leakage field at the expense of a narrower uniform-field region — a trade-off that must be evaluated per application.

From Raw Ore to Working Encoder: The Full Chain

To place the manufacturing process in context, it is worth tracing the complete supply chain that connects a permanent magnet to a working Magnetic Encoder on a production motor.

Neodymium is a rare earth element mined primarily in China, which currently accounts for approximately 85% of global rare earth production. The ore is refined into neodymium oxide, then reduced to metal. This metal is blended with iron and boron, melted in a vacuum induction furnace, strip-cast, hydrogen-decrepitated to break the ingot into coarse fragments, jet-milled to 3–7 µm powder, pressed under an aligning field, vacuum-sintered at 1,050–1,100°C, age-treated, ground to final dimensions using diamond tools, coated with nickel or epoxy, and finally magnetized by a capacitor discharge pulse. The finished magnet — which may be a disc just 6 mm in diameter and 2.5 mm thick — is then press-fit or adhesive-bonded to the end of a motor shaft, completing the core of the Magnetic Encoder assembly.

The entire sequence from raw material batching to finished magnetized part involves more than a dozen controlled process steps, each of which must be executed correctly to achieve the field uniformity and stability required for high-resolution position sensing. This complexity is why high-performance NdFeB encoder magnets are produced in specialized facilities with strict process controls and in-line magnetic testing rather than being a commodity item.

In the decades since Masato Sagawa patented the NdFeB magnet in 1982, the technology has been progressively refined to the point where neodymium permanent magnets now enable electric motors with permanent magnets that accounted for over half of Japan's industrial power demand as far back as 2005 — a figure that highlights how central these manufactured magnetic materials have become to modern energy and motion systems, including every Magnetic Encoder-based position feedback loop running in factories, robots, and vehicles worldwide.