What Are Circumferentially Magnetized Magnets?

Circumferentially magnetized magnets are magnets whose magnetic direction follows a circular or curved path instead of a simple straight direction. In this magnetization pattern, the magnetic direction runs along the circumference of the magnet body, rather than through the thickness, across the diameter, or from the inner radius to the outer radius.

This concept is most often discussed with ring magnets because a ring shape provides the clearest geometry for understanding circumferential magnetization. In a ring magnet, the magnetic direction can be considered to follow the circular path around the center hole.

This is different from axial magnetization, diametrical magnetization, radial magnetization, or multipole magnetization. In these common magnetization directions, the pole positions and working magnetic field are usually easier to identify from the outside.

Circumferential magnetization is also closely related to magnet orientation in some anisotropic magnet materials. Orientation refers to the preferred magnetic direction formed during material processing, while magnetization refers to the final magnetic state after the magnetizing process. For this reason, circumferential orientation and circumferential magnetization are often discussed together, especially for special AlNiCo magnet geometries.

For circumferentially magnetized magnets, the external pole pattern depends on the magnet geometry. In ring magnets, the magnetic path may follow a more closed circular path inside the magnet, so the magnet may not show simple north and south pole faces like common axial or diametrical magnets. As a result, the useful magnetic effect should be reviewed together with the magnet shape, material, working gap, and magnetic circuit design.

Circumferential Magnetization vs. Other Magnetization Directions

Magnetization direction describes how the magnetic field is arranged in relation to the magnet geometry. In common magnets, this direction is usually easier to recognize from the outside because the north and south poles appear on clear faces, sides, or repeated pole areas.

Circumferential magnetization is less intuitive. Instead of passing through the magnet along a straight direction, the magnetic direction follows a circular or curved path. For this reason, it is useful to compare circumferential magnetization with other common magnetization directions before discussing ring magnets, AlNiCo magnets, or special magnetic circuits.

Axial Magnetization

Diametrical Magnetization

Diametrical Multipole Magnetization

Radial Magnetization

Circumferential Magnetization

Circumferential Magnetization in Ring Magnets

Ring magnets can be magnetized in several different ways, and each magnetization direction changes how the magnetic field is used. Axially magnetized ring magnets have north and south poles on the two flat faces. Diametrically magnetized ring magnets have poles across the outside diameter. Radially magnetized ring magnets have magnetic direction between the inner diameter and outer diameter, so the inner and outer cylindrical surfaces become the main pole areas.

Circumferentially magnetized ring magnets are different from these common ring magnet structures. Their magnetic direction follows the circular path around the center hole, rather than pointing through the thickness, across the diameter, or between the inner and outer radius.

This distinction is important because circumferential magnetization cannot be judged only by the outer shape of the ring. A ring magnet may look similar from the outside, but axial, radial, diametrical, multipole, and circumferential magnetization create very different magnetic paths and working surfaces.

For circumferentially magnetized ring magnets, the useful magnetic effect is usually related to the internal circular magnetic path and the surrounding magnetic circuit. This is why they are more often discussed in special magnetic circuit designs than in general holding or simple attraction applications.

Circumferential Magnetization and AlNiCo Ring Magnets

Not every magnet material or magnet shape can achieve true circumferential orientation and magnetization. For many anisotropic magnets, the preferred magnetic direction is already formed during material processing, and the final magnetization must follow a direction that the material and magnetizing process can support.

AlNiCo ring magnets are often discussed with circumferential magnetization because this material can be related to special orientation and magnetizing methods. In a ring geometry, a circumferential magnetic field can be generated around an electrified straight conductor placed through the center hole. This field direction follows the circular path of the ring, making circumferential orientation and magnetization possible in suitable AlNiCo ring magnet designs.

This does not mean all AlNiCo ring magnets are circumferentially magnetized. Many AlNiCo ring magnets are still axially, diametrically, or otherwise magnetized according to the application. Circumferential magnetization should be specified intentionally, together with the magnet dimensions, AlNiCo grade, orientation requirement, working gap, and inspection method.

Compared with common Neodymium (NdFeB) magnets or Samarium Cobalt (SmCo) magnets, circumferentially magnetized AlNiCo ring magnets belong to a more specialized design category. The key question is not only magnetic strength, but whether the magnet can support the required circular magnetic path in the final magnetic circuit.

Curved Magnetic Paths and Horseshoe Magnets

Horseshoe magnets are sometimes discussed together with circumferential orientation because their magnetic path can follow a curved body instead of a simple straight line. In this sense, certain AlNiCo horseshoe-like magnets can be understood as magnets with an internal curved orientation path.

However, this should not be confused with circumferentially magnetized ring magnets. In ring magnets, circumferential orientation is usually discussed as a circular direction around the whole ring body. In horseshoe-like magnets, the internal direction may follow a curved path, but the orientation or magnetizing method is not the same as that used for ring magnets.

The magnetic circuit is still expressed through two open pole ends and the working gap between them. Therefore, horseshoe-like magnets can be related to curved or circumferential orientation, but they should not be treated as the same structure as circumferentially magnetized ring magnets.

Curved Magnetic Paths and Horseshoe Magnets

Can Arc Magnets Be Circumferentially Magnetized?

In most cases, arc magnets are not produced with true continuous circumferential magnetization. Although an arc magnet follows part of a circular shape, its magnetization direction does not automatically follow the same circular curve inside the magnet body.

For sintered Neodymium and Samarium Cobalt arc magnets, true circumferential orientation and magnetization are generally not available in the same way as special AlNiCo ring magnets. In practical designs, the intended circumferential direction is usually approximated by a straight-axis or chord magnetization direction.

This approximation may look close to circumferential magnetization in some arc magnet geometries, especially when the arc angle, magnet size, and working gap are suitable. Even so, it should not be described as true circumferential magnetization. The magnetic direction is still an approximation, not a continuous curved path inside the magnet body.

For this reason, arc magnet drawings should clearly indicate whether the requirement is true circumferential magnetization or an approximated circumferential direction. This avoids confusion between the arc shape, the magnetization direction, and the magnetic field required in the final assembly.

Ideal Circumferential Magnetization in Arc Magnets

Chord Magnetization in Arc Magnets

Applications in Hysteresis Couplings

Circumferentially magnetized or circumferentially oriented magnets are sometimes discussed in hysteresis couplings because these devices use a rotating magnetic field to transmit torque without direct mechanical contact.

In a hysteresis coupling, a driving magnetic field acts on a hysteresis material. As the magnetic field changes with rotation, the hysteresis material is repeatedly magnetized and remagnetized. Its magnetic response does not follow the applied field instantly, and this lag is what allows torque, slip, or braking behavior to be produced.

When the applied field does not drive the hysteresis material to full saturation, the material may operate through minor hysteresis loops. This is why hysteresis coupling is different from a simple permanent magnet coupling. The torque is not only created by direct magnetic attraction between two permanent magnet sets, but also by the energy and phase lag involved when the hysteresis material cycles through its magnetic response.

In this context, circumferential magnetization is related to the rotating magnetic circuit used in the design. The final performance still depends on the magnet arrangement, hysteresis material, air gap, dimensions, operating speed, and required torque behavior.

Minor Hysteresis Loops-Circumferentially Magnetized Magnets

Source: Arnold Magnetic Technologies

Need Circumferentially Magnetized Magnets?

Circumferential magnetization is most commonly reviewed in special AlNiCo magnet designs, especially when ring magnet geometry and the working magnetic circuit require a circular magnetic direction.

For AlNiCo ring magnets, magnet material, ring dimensions, orientation direction, magnetization method, and final magnetic performance should be reviewed together. This helps determine whether circumferential magnetization is suitable for the required magnetic circuit and application.