What are the properties of magnets? Magnets are extraordinary objects. They can push or pull on other things without actually touching them! People have known about magnets for thousands of years. In ancient Greece, people found remarkable rocks called lodestones that acted like magnets. The rocks could spin themselves to point north and south, lining up with the earth's magnetic field.
Today, magnets are used in lots of stuff we use every day. There is still much more to uncover about what the properties of magnets are and how we can utilize them.
Magnetic Materials
All things in the world show some kind of magnetism. But the strength of the magnetism is very different between things. Based on the properties of magnets, we have five big groups: ferromagnetic, paramagnetic, diamagnetic, ferrimagnetic, and antiferromagnetic.
Ferromagnetic things like iron, cobalt, and nickel show the strongest magnetism. Their tiny structure can explain their strong pull toward magnetic fields. The atoms in ferromagnetic things have unmatched electrons that point in the same direction within areas called magnetic domains. This pointing in the same direction increases the magnetic field and makes a permanent magnet.
Paramagnetic things like aluminum and platinum are also pulled towards magnetic fields, but the force is much weaker than in ferromagnetic things. The unmatched electrons in paramagnetic atoms point in the direction of an applied field but do not keep any magnetization once the field is removed.
Diamagnetic things like copper and gold show a weak push away from magnetic fields. When put in an external field, their atoms make an induced magnetic field in the opposite direction. However, they have no permanent atomic dipoles.
Ferrimagnetic things show complex magnetic ordering where the unmatched electrons of atoms on different lattices oppose each other, like in antiferromagnets. But ferrimagnets keep a permanent magnetization since the opposing unmatched electrons are unequal. Ferrites like magnetite are everyday ferromagnetic things.
Table 1: Magnetic Materials
Material | Magnetism | Examples |
Ferromagnetic | Very strong attraction to magnetic fields | Iron, cobalt, nickel |
Paramagnetic | Weak attraction to magnetic fields | Aluminum, platinum |
Diamagnetic | Weak repulsion from magnetic fields | Copper, gold |
Ferrimagnetic | Complex alignment, permanent magnetization | Magnetite, ferrites |
Antiferromagnetic | Complete alignment, no net magnetization | Chromium, manganese |
Magnetic Domains
All materials that are ferromagnetic have tiny magnets inside them called atomic dipoles. These tiny magnets usually point in random directions, so they cancel each other out. This means the material has no overall magnetism when left alone. But when the material becomes magnetized, the tiny magnets inside line up!
Magnetization happens when groups of atoms called magnetic domains get their tiny magnets to point the same way. The tiny magnets point together inside each domain because they are strongly connected. But different domains will point in random directions before magnetization happens.
External forces like magnetic fields can make the domains grow and line up their tiny magnets. This makes a permanent magnet. Heating a material also gives energy to the tiny magnets to move around. This lets domains line up their tiny magnets.
Other things that affect how domains of tiny magnets are arranged include stress, grain boundaries, impurities, and demagnetizing fields. The strength of a magnet depends on how many domains get their tiny magnets to line up and how well they resist external forces trying to mess them up.
Magnetic Fields
Magnets make invisible areas around them called magnetic fields. The magnetic flux is the space around a magnet where you can feel its force. To see the magnetic flux, we draw magnetic field lines. More lines mean a stronger magnetic field. The lines come out of the magnet's north pole and curve around to its south pole.
Magnetic fields happen when tiny electric charges move around. Inside atoms, the electrons spin and go around in orbits. Each atom is a tiny magnet with its own north and south poles. In magnetic materials, the tiny magnets in domains line up. This combines all their magnetic fields to make one big magnetic field pointing one way. This is how permanent magnets get such strong magnetic fields.
The invisible magnetic field is stronger and closer to the magnet. It gets weaker as you move farther away. Smaller magnets have smaller and weaker magnetic fields. Bigger magnets have bigger and stronger magnetic fields.
Magnetic Poles
Magnets have north and south poles. These are areas where the magnetic force is strongest. Opposite poles attract each other. North and south poles stick together. The same poles push away from each other. Two north poles or two south poles repel and push apart.
This happens because of the way the invisible magnetic field lines flow. The lines go from the north pole to the south pole inside the magnet. At the atomic level, each tiny magnet inside has magnetic field lines flowing north to south. In a magnet, all the tiny magnets line up their magnetic fields.
Permanent Magnets
While some materials like iron are naturally magnetic, permanent magnets are often artificially produced by magnetization. Iron, nickel, cobalt, or alloys usually make the best permanent magnets.
Magnetization involves exposing the material to a strong external magnetic field from an electromagnet or another permanent magnet. This causes the magnetic domains to grow and align with the external field, producing a strong permanent magnet. Hard magnets resist demagnetization, while soft magnets lose their magnetism more easily.
A permanent magnet's strength correlates with its coercivity, the field intensity needed to demagnetize it. High coercive materials can make powerful permanent magnets but are more challenging to magnetize initially. The maximum magnetic flux density or saturation magnetization and remnant magnetization also impact the magnet's strength.
Electromagnets
In addition to permanent magnets, electromagnets use electric currents to induce temporary magnetism. When an electric current goes through a coiled wire, it generates a magnetic field parallel to the coil's axis. The field strength increases with more loops and higher current.
The material inside the coil also matters. Soft iron makes the magnetic field stronger. Iron can make an electromagnet lift 100 times more. But iron also slows down how fast the magnet reacts.
Electromagnets need power to stay magnetic. Permanent magnets don't. But electromagnets can turn on and off fast. Their power can change instantly, too. This makes them suitable for lifting heavy iron and MRI scans that need changing magnetic fields.
Magnetic Strength and Magnetic Moment
How magnetic something is depends on how much magnetism happens near a magnetic field. How well it lines up with the magnetic field is called magnetic moment. This depends on the material's tiny building blocks called atoms, mainly electrons that are alone and not in pairs. These act like little magnets.
A strong magnet can hold a lot of magnetic power flowing through it. This is called saturation magnetization. A strong magnet keeps more of its magnetism when the external field disappears. This is called remanence. Magnetism comes from electrons spinning and orbiting. So tiny quantum physics rules control magnetic strength.
Magnetic Properties
Several fundamental properties of magnets help characterize magnetic performance:
● Saturation Magnetization: The maximum possible magnetic flux density a material can generate in an applied field. Measured in Teslas.
● Remanence: The remaining magnetization when the driving field is removed. How much magnetism remains?
● Coercively: The reverse magnetic field strength needed to demagnetize the material back to zero. Resists demagnetization.
● Permeability: Ability to support the formation of a magnetic field within itself. High permeability concentrates magnetic flux.
● Hysteresis: Tendency to retain an imposed magnetism. Materials with significant hysteresis make effective permanent magnets.
Optimizing these properties of magnets is essential in selecting the suitable magnetic material for a given application, whether achieving the highest permanent field strength or maximizing reversible flux changes.
Magnetic Hysteresis
Magnets can act in exciting ways! Magnets exhibit a phenomenon called hysteresis. Their magnetization follows a different path each time you cycle the external magnetic field. The precise path depends on the magnet's prior history of magnetization.
You can see this when you plot how the magnetic flux density B changes as the applied magnetic field H changes. This plot makes a loop called a hysteresis loop.
At first, the tiny magnetic regions in the magnet called domains slowly line up as you increase H. Once they are all lined up, further increases in H no longer change B. Then, when you reduce H, B follows a different curve. When H is zero, some magnetization remains left over from the aligned domains. You need to apply a magnetic field in the opposite direction to bring the magnetization back to zero.
The area inside the hysteresis loop shows energy lost as the domains change each cycle. Hard magnets have wide loops and significant energy losses. The shape of the loop also tells you about the magnet's properties, like how well it stays magnetized and how hard it is to demagnetize.
Temperature Effects
Heat energy can affect how magnets behave! As the temperature increases, the tiny aligned magnetic regions in a magnet called domains get jiggled around by the heat energy. This makes the magnetization go down. At a high Curie temperature, the heat energy messes up the magnetic order, and the permanent magnetism disappears completely.
How easy it is for a magnet to lose its magnetization depends on its Curie temperature. The highest Curie temperature of any pure element is iron at 1043 K. Adding stuff like nickel and cobalt to make alloys raises the Curie point higher. Heat-resistant permanent magnets let you use magnets in applications like generators and motors.
Cooling magnets below the Curie point makes the magnetization go up again. Superconducting electromagnets only work at cold temperatures where electrical resistance disappears to make powerful, lasting magnetic fields.
Table 2: Temperature Effects on Magnetism
Temperature Effect | Description |
Curie Temperature | Above this temperature, permanent magnetism is lost |
Thermal Agitation | Can disrupt the alignment of magnetic domains |
Cooling Below Curie Point | Increases magnetization as thermal motion decreases |
Cryogenic Temperatures | Enable superconducting electromagnets with persistent, high-strength fields |
Magnetic Applications
Magnets are a versatile tool found across the industrial landscape in applications like:
● Motors - Spinning electric motors rely on magnets converting between mechanical and electrical energy through electromagnetic induction. Small motors drive devices from fans to hard drives.
● Generators - Turbine generators produce electricity by rotating magnets near wire coils, inducing current flow.
● Magnetic storage - Hard disk drives write data by flipping the magnetization of tiny domains on a ferromagnetic disk.
● Levitation - Maglev trains use magnets to float above the track, eliminating friction for silent, smooth travel.
● Medical devices - MRI machines employ strong superconducting magnets to detect changes in the body's magnetic field for diagnostic imaging.
● Research - Mass spectrometers bend charged particles with magnetic fields to determine their mass and chemical structure.
● Renewable energy - Magnetic bearings stabilize flywheels, storing kinetic energy harvested from wind or solar sources.
Magnetic Levitation
Magnetic levitation, or maglev, uses magnets to make things float! Magnets push away from each other. But unique magnet setups can make stable floating.
Fast maglev trains already run in Asia and Europe. Floating above the track means no friction from wheels, so that maglev trains can go over 600 km/h! With no wheels or bearings, they are quieter and smoother to speed up and stop. They also use less energy than regular trains.
Maglev is valid for more than just trains! It could help launch spacecraft, make particle accelerators, create frictionless bearings, and stop vibration in buildings. Engineers are still improving super-strong magnets. This may let maglev trains connect whole cities in the future.
Adding more about how maglev works, real-world uses, and future possibilities explains this advanced concept simply. Young students can understand floating trains through frictionless magnet forces and imagine other applications of this cool technology.
Conclusion
From tiny refrigerator magnets to mile-long magnets powering fusion reactors, magnets are invaluable in our everyday lives. Understanding the unique properties of magnets continues to spur discoveries leading to novel applications. Cutting-edge areas like spintronics and magnetic monopoles hold possibilities for next-generation electronics and even quantum computers.
With much still to understand about the quantum foundations of magnetism, research will further unveil their tremendous potential. There remains so much more to discover about what the properties of magnets can enable us to achieve.
FAQs about Properties of Magnets
What are the units of magnetic field strength?
Magnetic field strength is quantified in amperes per meter (A/m) or teslas (T). One tesla equals one newton per ampere meter. The earth's magnetic field strength is around 0.5 gauss or 50 microteslas.
How do you calculate magnetic flux?
The magnetic flux through a surface is calculated by multiplying the magnetic field strength, the perpendicular area, and the cosine of the angle.
What materials are used in superconducting magnets?
Superconducting magnets typically use superconductors like niobium-titanium or niobium-tin coils cooled by liquid helium. Newer high-temperature superconductors allow less extreme cooling needs for high field strengths.
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