Axial vs Radial vs Multi-Pole Magnetization: How to Choose the Right Pattern

Quick Answer: For neodymium ring magnets, axial magnetization suits simple holding and coupling applications; radial (ID-to-OD) magnetization is standard for BLDC and PMSM motors where field lines must cross the air gap; multi-pole radial magnetization (8–72 poles) is the default for precision motors and encoders. Radial utilization is 15–20% higher than axial. Pole count is limited by minimum pole arc width (typically 3 mm) and magnetizing fixture capability.

This article, based on actual production data from Fullzen Technology's magnetizing workshop, helps you solve the core issues in magnetization direction selection:

Field distribution differences among four magnetization modes — axial, diametric, radial, and multi-pole (not just definitions, but quantitative comparisons)

Motor-type-to-magnetization-mode decision matrix: which to choose for BLDC/PMSM/stepper/encoders

Quantitative basis for pole count selection: relationships between pole count and torque density, cogging torque, and efficiency

Real-world data on magnetizing fixture costs and process lead times

Standard quality inspection procedures after magnetization

Magnetization Basics: Why Direction Matters for Ring Magnets

Magnetization direction is not a post-production choice — it is determined during the pressing stage and cannot be changed afterward. Understanding this upfront saves costly redesigns.

How Magnetization Is Set During Manufacturing

Many people assume that magnetization direction is determined during the magnetizing step. In fact, it is not. For sintered neodymium ring magnets, the domain orientation direction is locked in during the pressing stage by an applied external magnetic field — this is the defining characteristic of anisotropic materials.

Here is the full process:

Pressing stage: A orienting magnetic field is applied in the die to align the easy magnetization axis of Nd₂Fe₁₄B grains to the target direction.

Sintering stage: High-temperature densification "freezes" the crystal orientation into the blank.

Magnetizing stage: A pulsed strong magnetic field flips all oriented domains into place — if the orientation and magnetizing directions align, optimal magnetic performance is achieved.

This is why the magnetization direction must be specified at the time of ordering: the pressing die's orientation direction is customized to your requirements. Once sintering is complete, the orientation cannot be changed.

Anisotropic vs Isotropic: What This Means for Your Design

Before selecting a magnetization mode, you need to understand the basic material classifications:

Anisotropic sintered NdFeB: Magnetic performance is optimal along the orientation axis; performance drops sharply beyond 30° deviation. Suitable for axial, radial, diametric, and other directional magnetization.

Isotropic bonded NdFeB: No preferential orientation direction; can be magnetized in any direction, but maximum energy product is 30–40% lower than sintered. Suitable for multi-pole and complex magnetization patterns.

Isotropic injection-molded NdFeB: Lowest magnetic performance, but can be injection-molded into complex shapes and supports post-magnetization. Suitable for special geometries.

At Fullzen Technology, over 85% of monthly ring magnet shipments are anisotropic sintered NdFeB — because motor customers demand the highest magnetic performance. Bonded magnets are primarily used for multi-pole encoder rings.

Learn about neodymium ring magnets in standard and custom configurations (sizing, tolerances, and material selection — see our dimension guide).

The Four Magnetization Patterns for Ring Magnets

Ring magnets support four distinct magnetization patterns, each producing a fundamentally different magnetic field distribution that determines which applications they can serve effectively.

Axial Magnetization (Single-Axis Through-Thickness)

The magnetic field runs along the axial (thickness) direction of the ring magnet, with the N pole on one end face and the S pole on the other. This is the simplest and lowest-cost magnetization method.

Characteristics:

Field crosses the entire thickness direction; flux lines run from one end face to the other.

Simplest magnetizing fixture — two parallel plates are sufficient.

Yield >98% because field direction is easy to control.

Good surface field uniformity, suitable for scenarios requiring uniform attraction.

Typical applications: Magnetic coupling, holding fixtures, magnetic door locks, simple sensors. Rarely used in motors because the axial field cannot effectively cross the air gap to drive rotor rotation.

Diametric Magnetization (Cross-Section)

The magnetic field runs along the diameter direction of the ring magnet, with N on one side and S on the opposite side. Note: This is relatively uncommon in ring magnets and is more typical for cylindrical/disc magnets.

Characteristics:

Field runs across the cross-section; flux lines travel from one side of the ring through to the opposite side.

Requires a dedicated diametric magnetizing fixture, costing 3–5× more than axial.

In ring magnets, diametric magnetization offers lower field utilization than radial magnetization.

Diametric magnetization is rarely used in ring magnets. If your application requires a field across the cross-section, radial magnetization (ID-to-OD) is usually the better choice. Diametric magnetization is primarily used in cylindrical magnets.

Radial Magnetization (ID-to-OD)

The magnetic field runs radially — from the inner diameter (ID) to the outer diameter (OD), or from OD to ID. This is the most common magnetization method for ring magnets in motor applications.

Characteristics:

Flux lines emerge from the bore, cross the air gap, and reach the outer surface — perfectly matching the motor's magnetic circuit structure.

Radial magnetization offers 15–20% higher magnetic energy utilization than axial because the field direction aligns with the air-gap flux path.

Requires a dedicated ID-to-OD magnetizing fixture with an inner pole core inserted into the bore and an outer pole sleeve wrapping the OD.

Magnetizing difficulty and cost are higher than axial (fixture complexity 5–20× greater).

Typical applications: BLDC motors, PMSM motors, servo motors, generators, magnetic couplers. At Fullzen Technology, radial magnetization accounts for over 70% of orders from motor customers.

For complete specifications and capacity information on radially magnetized ring magnets, see our radially magnetized ring magnets for motor applications.

Multi-Pole Magnetization (N-S Alternating)

N and S poles alternate along the circumference of the ring magnet, forming multiple pole pairs. This is the standard choice for precision motors and encoders.

Characteristics:

Poles alternate around the circumference: N-S-N-S..., ranging from 2 pole pairs (4 poles) up to 36 pole pairs (72 poles).

More poles yield higher air-gap field frequency, lower torque ripple, and higher encoder resolution.

Each pole count requires a dedicated magnetizing fixture — more poles mean more complex fixture design and manufacturing.

Can be implemented as multi-pole radial magnetization (ID-OD alternating) or multi-pole axial magnetization (end-face alternating).

Typical applications: BLDC/PMSM motor rotors, magnetic encoders, torque motors, direct-drive motors. At Fullzen, common pole counts for multi-pole ring magnets are 8/10/12/14/16/24/32/48/64/72 poles.

Magnetization Pattern Comparison: Performance Numbers

The table below consolidates the key performance parameters that engineers need to compare when selecting a magnetization pattern for their application.

Parameter	Axial	Diametric	Radial (Single Pole-Pair)	Multi-Pole Radial
Field direction	Thickness (N-face→S-face)	Cross-section	ID → OD	Circumferential alternating N-S
Magnetic energy utilization	Baseline (100%)	~80-85%	15–20% higher than axial	Same as radial, with slight multi-pole loss
Fixture complexity	Lowest (parallel plates)	Medium (diameter plates)	High (ID-OD pole cores)	Highest (multi-pole cores)
Fixture cost level	$	$$	$$-$$$	$$$-$$$$
Yield	>98%	>95%	>93%	>90%(decreases with more poles)
Typical pole count	1 pair (2 poles)	1 pair (2 poles)	1 pair (2 poles)	4–36 pairs (8–72 poles)
Lead time (incl. fixture)	Standard	+3-5days	+5-7days	+7-14days
Motor suitability	Low	Low (not suitable for rings)	High	Highest
Encoder suitability	Not suitable	Not suitable	Low resolution	High resolution

 

These data reveal one core fact: although radial magnetization (including multi-pole) carries higher fixture costs and longer lead times, its magnetic energy utilization and motor compatibility far exceed those of axial magnetization. This is why, among Fullzen's motor customers, over 70% choose radial or multi-pole magnetization.

[Note] Fixture cost levels are relative references. Actual costs depend on ring OD, wall thickness, and pole count. An 8-pole multi-pole fixture for 30 mm OD costs approximately $800–1,200; a 24-pole fixture for 60 mm OD costs approximately $2,500–4,000.

Motor Type → Magnetization Pattern: The Decision Matrix

This matrix maps the most common motor architectures to their optimal magnetization pattern, based on our production data from Fullzen Technology.

This is what almost no competitor offers — a straightforward decision matrix you can follow directly. Different motor architectures have completely different requirements for magnetization mode; choosing incorrectly doesn't just reduce performance — it simply won't run.

BLDC Inrunner Motors

Inrunner BLDC motors: stator on the outside, rotor (magnets) rotating on the inside.

Recommended magnetization mode: Multi-pole radial magnetization (ID-to-OD direction, alternating N-S)

Typical pole counts: 8/10/12/14 poles (4–7 pole pairs)

Reason: The radial field crosses the air gap directly, synchronizing with the rotating field generated by the stator windings. Higher pole counts yield lower torque ripple.

Fullzen shipment share: Among inrunner BLDC customers, 95% choose multi-pole radial magnetization.

BLDC Outrunner Motors

Outrunner BLDC motors: rotor (magnets) rotating on the outside, stator on the inside. Common in drones and low-speed direct-drive applications.

Recommended magnetization mode: Multi-pole radial magnetization (OD-to-ID direction, alternating N-S — opposite to inrunners)

Typical pole counts: 12/14/16/24 poles (6–12 pole pairs)

Reason: The outrunner's magnets surround the stator; the radial field runs from OD to ID, again aligning with the air-gap flux path.

Note: Pole counts are typically 2–4 poles higher than inrunners because outrunners have larger diameters and can accommodate more poles.

PMSM and Servo Motors

Recommended magnetization mode: Multi-pole radial magnetization (Halbach arrays may be used in high-end applications)

Typical pole counts: 8/10/12 poles

Halbach array: A special magnetization arrangement that enhances the field on one side while canceling it on the other. Suitable for servo motors with extremely high torque-density requirements.

Fullzen capability: Supports Halbach array magnetization, with minimum OD 25 mm and maximum OD 120 mm.

Stepper Motors

Recommended magnetization mode: Multi-pole radial magnetization

Typical pole count: 50 teeth (100 poles) is standard for hybrid stepper motor construction.

Note: Stepper motor rotor structures are quite special — typically not simple ring magnets but toothed claw-pole structures. However, some high-end permanent magnet stepper motors do use multi-pole ring magnets.

Magnetic Encoders and Position Sensors

Recommended magnetization mode: Multi-pole radial magnetization (or bonded NdFeB multi-pole rings)

Typical pole counts: 32/64/128/256 poles — pole count directly determines encoder resolution.

Material selection: High-pole-count encoder rings typically use isotropic bonded NdFeB because bonded materials can be injection-molded and freely magnetized without the constraints of pressing orientation.

Key parameters: Inter-pole angular accuracy <0.5°, magnetic field waveform sinusoidal purity >99%.

[Note] Encoder ring precision requirements are far higher than those for motor magnets. At Fullzen, encoder rings are produced on a dedicated production line, with pole-pitch tolerance controlled within ±0.02 mm.

Axial Flux Motors (Emerging Applications)

Recommended magnetization mode: Axial magnetization or multi-pole axial magnetization

Explanation: Axial flux motors (disc motors) have a different magnetic circuit direction from radial flux motors — the field runs axially across the air gap. These motors are seeing rapid growth in new energy vehicles and robotics.

Current status: Fullzen has begun supplying axial multi-pole ring magnet samples for axial flux motor customers, with OD range 40–200 mm.

Pole Count Selection: How Many Poles Do You Actually Need?

Pole count directly affects torque density, cogging torque, and encoder resolution — but there are physical limits based on ring diameter and minimum pole arc width.

More poles on a multi-pole ring is not always better. Pole count selection requires balancing three factors: torque density, cogging torque, and physical limits.

Pole Count vs Torque Density

Effect of increasing pole count on torque density:

4 poles → 8 poles: Torque density increases by approximately 12–18%

8 poles → 16 poles: Torque density increases by approximately 8–12%

16 poles → 24 poles: Torque density increases by approximately 5–8%

Above 24 poles: Improvement flattens; diminishing returns set in.

The pattern is clear: the greatest benefit comes from upgrading from lower to higher pole counts. 8 poles are significantly better than 4 poles, but 24 poles are only marginally better than 16 poles.

Pole Count vs Cogging Torque

Cogging torque — the torque ripple when the motor is unpowered — directly causes vibration and noise at low speeds. Higher pole counts reduce cogging torque:

4 poles: Highest cogging torque; suitable for applications with low smoothness requirements.

8–12 poles: Cogging torque significantly reduced; covers most BLDC applications.

16+ poles: Extremely low cogging torque; suitable for precision servos and low-speed direct drive.

The effect of pole count on cogging torque is more pronounced than its effect on torque density — which is why many customers choose to increase pole count when optimizing motor smoothness.

Maximum Pole Count Constraints

Pole count cannot be increased arbitrarily; three physical constraints apply:

Minimum pole arc width: Each pole requires at least 3 mm of arc width (for sintered NdFeB). Below this value, magnetization becomes uneven and field strength unstable.

OD constraint: Pole count × pole arc width ≤ π × OD. For example, a 30 mm OD ring has an outer circumference of ≈94 mm, allowing approximately 31 poles maximum — but accounting for inter-pole gaps, the practical limit is 20–24 poles.

Magnetizing fixture precision: Higher pole counts require higher positional accuracy for each pole core in the fixture. Above 24 poles, fixture costs increase sharply.

At Fullzen Technology, we recommend 8–16 poles for OD below 30 mm, 12–24 poles for OD 30–60 mm, and 16–32 poles for OD 60–100 mm. Applications exceeding 32 poles require individual feasibility assessment.

[Note] The upper pole-count limit is also affected by wall thickness. Thin-wall rings (wall thickness <3 mm) have lower pole-count limits due to increased inter-pole flux leakage. For specific calculations, please contact our engineering team.

Magnetization Process: What Happens Behind the Scenes

The magnetization step is the final and most irreversible stage in ring magnet production — here's what happens in our workshop and how it affects your timeline and cost.

Magnetizing Fixture Design and Cost

The magnetizing fixture is the most critical component in the magnetization process. Different magnetization methods correspond to different fixture structures:

Axial magnetization fixture: Two parallel copper plates — simplest structure, lowest cost ($100–300). Good universality; fixtures can be shared across different grades of the same size.

Radial magnetization fixture: Inner pole core + outer pole sleeve construction, requiring precise concentricity (<0.05 mm). Cost: $600–2,000 (depending on size).

Multi-pole magnetization fixture: Each pole corresponds to an independent pole core; more poles mean greater complexity. 8-pole fixture: $800–1,200; 24-pole: $2,500–4,000; 48+ poles: $5,000–8,000+.

Fixtures are a one-time investment — if your order requires ongoing production of the same pole count, the fixture cost amortizes to a very low per-piece cost. In pilot stages, we recommend starting with a lower pole count to validate the magnetic circuit design.

Pulse Magnetization Parameters

Magnetization is the process of using an instantaneous strong magnetic field to flip all magnetic domains to the target orientation. Key parameters:

Field strength: Must exceed the material's intrinsic coercivity (Hcj) to achieve full magnetization. N42 requires >955 kA/m; 42SH requires >1,710 kA/m.

Pulse width: Typically 0.5–5 ms, depending on magnet volume and material.

Saturation criterion: Measure flux after magnetization; if deviation from standard value exceeds 3%, magnetization is insufficient and pulse energy needs to be increased.

At Fullzen Technology's magnetizing workshop, we use a 5,000 V / 1,000,000 μF pulse magnetizer, capable of meeting magnetization requirements from N35 to 50EH grades and from 2 to 72 poles.

Sintered vs Bonded vs Injection-Molded Ring Magnetization Differences

Magnetization processes differ significantly among the three material types:

Sintered NdFeB (anisotropic): Requires extremely strong pulsed fields (>3 T) for full magnetization. Orientation direction is established during pressing; magnetization direction must align with orientation direction. Irreversible after magnetizing.

Bonded NdFeB (isotropic): No preferential orientation direction; can be magnetized in any direction. Requires lower magnetizing field strength (>1.5 T); multi-pole magnetization easily achieves complex patterns. But maximum energy product is 30–40% lower than sintered.

Injection-molded NdFeB (isotropic): Lowest magnetic performance (BHmax ≈5–10 MGOe), but can be injection-molded into complex shapes and magnetized afterward. Suitable for irregular shapes and ultra-thin multi-pole rings.

Which material to choose for your magnetizing ring depends on your application's prioritization of magnetic performance vs magnetization-pattern complexity. For high performance, choose sintered; for complex patterns, choose bonded.

Quality Inspection After Magnetization

Every magnetized ring must pass inspection before shipment — here are the three standard methods we use at Fullzen Technology and what each one verifies.

Helmholtz Coil Measurement (Total Flux)

The Helmholtz coil measures the magnet's total magnetic flux — the most fundamental method for verifying full magnetization.

Principle: Place the magnet inside the Helmholtz coil, measure induced voltage, and calculate total flux.

Purpose: Verify that magnetization has reached saturation and that flux values are within tolerance (typically ±5%).

Limitation: Can only measure total flux; cannot determine whether field distribution is uniform or whether inter-pole symmetry exists.

Every Fullzen magnet must pass Helmholtz coil testing before shipment — this is the first step in our standard QC process.

Hall Probe Scanning (Field Distribution)

Hall probe scanning measures the magnetic field distribution across the magnet surface — particularly important for multi-pole rings.

Principle: A Hall probe rotates and scans along the magnet surface, recording field strength at each angular position.

Purpose: Verify inter-pole symmetry, field waveform (sinusoidal/square-wave purity), and pole-pitch consistency in multi-pole rings.

Key metric: Field deviation between adjacent poles should not exceed ±3%; encoder rings require ±1%.

Encoder customers typically require Hall probe scan reports. At Fullzen, this is a standard QC item for encoder rings.

Iron Powder Method (Quick Visual Check)

The iron powder method is the most intuitive qualitative inspection method — iron powder sprinkled on the magnet surface aligns along the flux lines, directly revealing the field distribution.

Purpose: Quick verification that magnetization direction is correct, pole count is correct, and there are no obvious magnetization defects.

Limitation: Qualitative only; provides no numerical values. Accuracy is far below that of Hall probe scanning.

The iron powder method is typically used for first-article inspection and rapid sorting on the production line — not suitable for outgoing QC, but excellent for incoming inspection and quick post-magnetization confirmation.

FAQ

Q: Can a ring magnet be remagnetized in a different direction after initial magnetization?

A: No. For sintered NdFeB ring magnets, the magnetic orientation is determined during the pressing stage. Once magnetized, re-magnetizing in a different direction will not work because the magnetic domains are already aligned. If you need to change magnetization direction, you must order new magnets with the correct orientation specified before pressing. At Fullzen Technology, we confirm the magnetization direction in the drawing review stage to avoid this issue.

Q: How many poles can a 30 mm OD ring magnet support?

A: A 30 mm OD ring magnet can typically support up to 16–20 poles, depending on wall thickness and minimum pole arc width. With a minimum pole arc of 3 mm, the outer circumference allows approximately 31 poles maximum, but practical constraints — magnetizing fixture precision, wall thickness, and inter-pole flux leakage — limit most designs to 16–20 poles. We recommend confirming your pole count with our engineering team before ordering fixtures.

Q: Why is radial magnetization more expensive than axial?

A: Radial magnetization requires a custom fixture that generates a strong radial field from ID to OD, which is more complex to design and manufacture than a simple axial plate fixture. Radial fixtures typically cost 5–20 times more than axial fixtures ($600–$6,000+ depending on ring size and pole count). Additionally, radial magnetization has a lower yield rate (typically 90–95% vs 98%+ for axial) due to the higher field strength requirements and alignment precision needed.

Q: What magnetization pattern is best for BLDC motors?

A: For most BLDC motors, multi-pole radial magnetization is the standard choice. Inrunner BLDC motors typically use 8–14 poles; outrunner motors use 12–24 poles. The radial field direction (ID-to-OD) aligns with the air gap flux path, providing 15–20% higher utilization than axial magnetization. At Fullzen Technology, over 70% of our motor customer orders specify multi-pole radial magnetization.

Q: What is the maximum operating temperature for multi-pole ring magnets?

A: Multi-pole ring magnets follow the same temperature limits as standard ring magnets — N35–N45 grades work up to 80°C, while SH grades handle 150°C and UH grades handle 180°C. However, multi-pole rings face higher demagnetization risk at elevated temperatures because the thin pole sections have lower self-demagnetization resistance. For motor applications above 120°C, we recommend using 38SH or 40UH grade rather than standard N42.