What a Magnet Is
Magnet Guide is an independent English-language information guide to magnetism and its practical meaning. Magnets work through two connected ideas: magnetic materials and the fields they produce. A field describes where a magnetic effect can be detected, including the space around a magnet rather than only its surface. These concepts help explain why some objects respond to a magnet while others show no noticeable attraction in ordinary conditions.
Magnetic materials
A magnet is an object or material that produces a magnetic field. The field can exert a force on certain other materials, even when the magnet and the material are not touching. Iron, nickel, and cobalt are familiar ferromagnetic examples: they can be strongly attracted to a magnet because their internal magnetic regions can respond to an applied field.
In everyday conditions, an iron nail or a steel paper clip is commonly pulled toward a household magnet, while a piece of wood, glass, or dry plastic is not. Many metals do not show noticeable attraction to an ordinary hand magnet; copper and aluminum, for example, are not pulled across a table in the way an iron object is. This distinction is about the strength of the response under ordinary conditions, not simply whether an object looks metallic.
Objects made from mixtures of metals can behave differently depending on their composition. Some stainless steels are attracted to magnets, while others show little or no noticeable attraction. For a simple check, bring a magnet close without contact: a clear pull indicates a responsive material, while no visible movement means the material is not appreciably attracted in that setup.
Magnetic fields
A magnetic field is the region around a magnet where magnetic forces can act. It extends beyond the magnet’s surface, so a small iron object can move toward a magnet before the two make contact. The effect generally becomes weaker as the distance increases; even a gap of a few centimetres can make a difference for a small refrigerator magnet and a light object.
You cannot see a magnetic field directly, but you can represent its effects with magnetic field lines. These lines are a diagram, not physical threads in the air. At each point, the line’s direction shows the direction a small compass needle would point, and the spacing of the lines represents relative field strength: closer spacing indicates a stronger field in that region.
A compass provides a practical way to detect field direction. Place it near a magnet and the needle turns to align with the local field; move the compass to another position and its direction can change. Field diagrams make these changes easier to compare, while keeping in mind that the drawn lines summarize a continuous effect around the magnet rather than marking separate tracks followed by magnetic force.
Poles, Attraction, and Repulsion
A bar magnet’s two ends are called its north and south poles, and their labels describe a consistent convention for identifying its orientation. The interaction between poles explains why two magnets may pull together or push apart. When comparing magnets, focus on which poles face one another. Field-line diagrams help represent these relationships, but the lines are not physical objects.
North and south poles
For an ordinary bar magnet, the north pole is the end that points toward geographic north when the magnet is freely suspended. The opposite end is the south pole. This naming convention identifies the magnet’s orientation; it does not mean that either end exists independently. Every ordinary bar magnet has both a north pole and a south pole.
Cutting a bar magnet across its length does not leave one piece with only a north pole and the other with only a south pole. Each fragment becomes a smaller magnet with its own pair of poles. For example, if a bar is cut across its middle, the newly exposed faces become opposite poles: the cut face on one fragment is north, and the facing cut face on the other is south. The original outer ends retain their respective poles.
At the scale of an ordinary magnet, cutting changes the boundaries of the magnetized material; it does not separate north from south. A single isolated pole is therefore not produced by breaking or cutting a bar magnet.
How poles interact
When two magnets are brought close together, the poles facing one another determine whether they pull together or push apart. Unlike poles attract, while like poles repel. The same rule applies whether the magnets are held end-to-end or positioned side by side; the orientation of the facing poles matters.
| First pole | Facing pole | Interaction |
|---|---|---|
| North | North | Repel |
| South | South | Repel |
| North | South | Attract |
Field lines are a diagrammatic way to show the direction and pattern of a magnetic field, not visible threads stretching between magnets. In a standard diagram, arrows outside a magnet run from north toward south; closer spacing represents a stronger field. The lines help explain why opposite poles draw together and matching poles push apart, but they are not material strands that touch or carry the force.
Permanent Magnets and Electromagnets
Permanent magnets and electromagnets both produce magnetic fields, but their field sources differ. A permanent magnet can retain magnetization without continuous current, while an electromagnet’s field is associated with current flowing through a coil. This difference affects how each type is controlled and where it is practical to use. Comparing their operation clarifies why compasses, lifting equipment, and electric motors may use different magnet arrangements.
How the two types differ
The main distinction is whether magnetization is retained by the material or produced by current in a coil. The table compares field source, power needs, control, and common applications.
| Aspect | Permanent magnet | Electromagnet |
|---|---|---|
| Field source | Aligned magnetic domains in a magnetized material; the magnet retains its field without a supply circuit. | Current in a wire coil creates the field; a soft iron core is often added to strengthen it. |
| Continuous current | 0 A from an external supply is needed to maintain magnetization. | Nonzero coil current is needed while the energized field is required. |
| Control | Field is not switched off electrically; its effect can be changed by moving the magnet or changing its position relative to an object. | A switch or current control can energize, weaken, or stop the coil’s field; reversing current reverses its magnetic orientation. |
| Typical applications | Compass needles use a small permanent magnet, and some electric motors use permanent magnets as part of their design. | Lifting equipment can use an energized coil to hold ferrous loads, while other electric motor designs use electromagnets. |
For permanent magnets, retained magnetization makes a continuing power connection unnecessary. An electromagnet instead links its field to the current supplied to its coil, so the field can be controlled during operation. Motor designs vary: some use permanent magnets, while others use electromagnets or combine magnetic components in different ways.
Common Magnet Materials
Permanent magnets are made from different materials, and their performance depends on the alloy or ceramic composition. Neodymium-iron-boron, ferrite, and alnico each offer a different balance of magnetic strength, temperature tolerance, and resistance to corrosion. A compact magnet made from one material may suit a design better than a larger magnet made from another. Compare the operating conditions and required holding force before choosing a material.
Neodymium magnets
Neodymium magnets are made from neodymium-iron-boron, usually abbreviated NdFeB; they are an alloy, not pieces of pure neodymium. Their high magnetic strength allows compact designs to provide substantial force.
- NdFeB magnets generally provide greater magnetic strength per unit volume than ferrite or alnico, making them useful where a small magnet must deliver strong attraction.
- Temperature limits depend on grade: many standard N-grade magnets have a maximum operating temperature near 80°C, while heat-resistant grades can reach roughly 150–200°C.
- Heating can reduce performance, and exceeding a grade’s limit may cause irreversible loss of magnetization; check the manufacturer’s rating for the actual operating conditions.
- Uncoated NdFeB can corrode when exposed to moisture, so common finishes include nickel-copper-nickel plating, zinc, or epoxy, selected for the environment.
- Compact motors, sensors, headphones, and magnetic closures can benefit from their strength, especially when space is limited and the temperature and exposure conditions suit the grade.
Choose the grade and coating together: a strong magnet that overheats or corrodes may not meet the application’s service requirements. For outdoor or humid use, evaluate the coating and enclosure as well as the magnet itself.
Other permanent-magnet materials
Ferrite and alnico are distinct permanent-magnet materials with different strength and environmental characteristics. The grade, magnet shape, and operating conditions affect actual performance, so the values below are typical rather than universal.
| Material | Composition and typical strength | Temperature behavior | Corrosion considerations | Suitable application contexts |
|---|---|---|---|---|
| Ferrite (ceramic) | Iron oxide with strontium or barium compounds; typical maximum energy product is about 3–5 MGOe. | Many grades operate to about 250°C, depending on grade and design. | Ceramic composition resists rust and corrosion well; no metallic plating is usually needed. | Cost-conscious motors, loudspeakers, magnetic catches, and outdoor assemblies where moderate strength is sufficient. |
| Alnico 5 | Iron alloy containing aluminum, nickel, and cobalt; typical maximum energy product is about 5 MGOe. | Can operate at temperatures approaching 500°C, depending on grade and conditions. | Generally good corrosion resistance, though surface protection may be appropriate in harsh environments. | High-temperature sensors, instruments, and applications that need stable magnetization in heat. |
| Alnico 8 | Aluminum-nickel-cobalt iron alloy; typical maximum energy product is about 5–6 MGOe. | High-temperature performance is a key benefit; limits vary by grade and assembly. | Usually resists corrosion well, but exposed surfaces may need protection in wet or chemical environments. | Magnetic assemblies requiring higher coercivity than many other alnico grades, including some motors and sensors. |
Ferrite is often a practical choice when corrosion resistance and cost matter more than compact size. Alnico suits hot operating environments; match its grade to the required magnetic force and assembly conditions.
Magnet Shapes and Applications
A magnet’s shape affects how it can be fixed in place and where its useful field is concentrated. The best choice depends on the available mounting space, the direction in which the magnet is magnetized, and the position of nearby parts. Discs, cylinders, rings, blocks, and bars suit different mechanical layouts. Comparing those features helps connect a magnet’s geometry to its intended task.
Comparing common shapes
Shape selection starts with the mounting method and the direction the field must face. A hole, flat face, or long axis can make installation simpler in a particular assembly.
| Shape | Mounting options | Practical field orientation | Common application needs |
|---|---|---|---|
| Disc | Bond its flat face to a surface, or seat it in a shallow circular recess. | Often magnetized axially, with poles on the two flat faces; diametric magnetization is also possible. | Useful for compact face-to-face holding, sensors, and small closures where a broad flat contact is convenient. |
| Cylinder | Fit the round body into a drilled hole or cylindrical holder; retain it with adhesive or a close-fitting seat. | Axial magnetization places poles at the circular ends; diametric magnetization places them on opposite sides of the curved wall. | Fits rods, housings, and narrow openings where a round profile is easier to accommodate than a block. |
| Ring | Pass a shaft or fastener through the central opening, or bond one annular face to a plate. | Axial magnetization gives opposite poles on the ring’s flat faces; radial or diametric arrangements serve different assemblies. | Suited to rotating components, shaft-mounted assemblies, and layouts that need a central clearance. |
| Block | Bond a broad face, clamp the sides, or locate it in a rectangular pocket. | Magnetization can run through thickness, width, or length, depending on which faces need to act as poles. | Works well on flat panels and in fixtures where a rectangular footprint provides stable contact. |
| Bar | Place it in a simple holder or support it along its length without needing a central hole. | Typically magnetized along its length, with poles at opposite ends. | Useful for demonstrations and layouts that benefit from a long, clearly defined pole-to-pole field pattern. |
Choose the geometry that fits the assembly first, then specify magnetization direction to place the active faces where the design needs them. A ring suits a shaft, a block suits a flat mounting surface, and a disc or cylinder fits compact round seats.
Bar magnets
A bar magnet is an elongated rectangular or rod-like magnet whose length is greater than its width and thickness. In the common arrangement, it is magnetized along its long axis, so the north and south poles lie at opposite ends. This geometry makes the pole locations easy to identify and gives the surrounding field a clear end-to-end pattern.
That clarity makes bar magnets useful in classroom demonstrations, where a compass can be moved around the magnet to trace the field, or iron filings can reveal its overall shape. In practical assemblies, a bar can be held in a simple cradle or mounted along a flat support. It suits tasks that need a long magnetic element with accessible opposite ends, such as positioning a target across a narrow gap. Its straightforward shape also makes pole-to-pole alignment easier to observe than with a ring or compact disc.