What Is Magnetism?
Learn the definition of magnetism, discover the types of magnetic materials, and get interesting magnetism facts.
A Simple Introduction to Magnetism
Helmenstine holds a Ph.D.
in biomedical sciences and is a science writer, educator, and consultant.
She has taught science courses at the high school, college, and graduate levels.
Magnetism is defined as an attractive and repulsive phenomenon produced by a moving electric charge.
The affected region around a moving charge consists of both an electric field and a magnetic field.
The most familiar example of magnetism is a bar magnet, which is attracted to a magnetic field and can attract or repel other magnets.
Ancient people used lodestones, natural magnets made of the iron mineral magnetite.
In fact, the word "magnet" comes from the Greek words magnetic lithos, which means "Magnesian stone" or lodestone.
Thales of Miletus investigated the properties of magnetism around 625 BCE to 545 BCE.
The Indian surgeon Sushruta used magnets for surgical purposes around the same time.
The Chinese wrote about magnetism in the fourth century BCE and described using a lodestone to attract a needle in the first century.
However, the compass didn't come into use for navigation until the 11th century in China and 1187 in Europe.
While magnets were known, there wasn't an explanation for their function until 1819, when Hans Christian Ørsted accidentally discovered magnetic fields around live wires.
The relationship between electricity and magnetism was described by James Clerk Maxwell in 1873 and incorporated into Einstein's theory of special relativity in 1905.
Causes of Magnetism
So, what is this invisible force? Magnetism is caused by the electromagnetic force, which is one of the four fundamental forces of nature.
Any moving electric charge ( electric current ) generates a magnetic field perpendicular to it.
In addition to current traveling through a wire, magnetism is produced by the spin magnetic moments of elementary particles, such as electrons.
Thus, all matter is magnetic to some degree because electrons orbiting an atomic nucleus produces a magnetic field.
In the presence of an electric field, atoms and molecules form electric dipoles, with positive-charged nuclei moving a tiny bit in the direction of the field and negative-charged electrons moving the other way.
All materials exhibit magnetism but magnetic behavior depends on the electron configuration of the atoms and the temperature.
The electron configuration can cause magnetic moments to cancel each other out (making the material less magnetic) or align (making it more magnetic).
Increasing temperature increases random thermal motion, making it harder for electrons to align, and typically decreasing the strength of a magnet.
Magnetism may be classified according to its cause and behavior.
The main types of magnetism are:
Diamagnetism: All materials display diamagnetism, which is the tendency to be repelled by a magnetic field.
However, other types of magnetism can be stronger than diamagnetism, so it is only observed in materials that contain no unpaired electrons.
When electrons pairs are present, their "spin" magnetic moments cancel each other out.
In a magnetic field, diamagnetic materials are weakly magnetized in the opposite direction of the applied field.
Examples of diamagnetic materials include gold, quartz, water, copper, and air.
Paramagnetism: In a paramagnetic material , there are unpaired electrons.
The unpaired electrons are free to align their magnetic moments.
In a magnetic field, the magnetic moments align and are magnetized in the direction of the applied field, reinforcing it.
Examples of paramagnetic materials include magnesium, molybdenum, lithium, and tantalum.
Ferromagnetism: Ferromagnetic materials can form permanent magnets and are attracted to magnets.
A ferromagnet has unpaired electrons, plus the magnetic moments of the electrons tend to remain aligned even when removed from a magnetic field.
Examples of ferromagnetic materials include iron, cobalt, nickel, alloys of these metals, some rare earth alloys, and some manganese alloys.
Antiferromagnetism: In contrast to ferromagnets, the intrinsic magnetic moments of valence electrons in an antiferromagnet point in opposite directions (anti-parallel).
The result is no net magnetic moment or magnetic field.
Antiferromagnetism is seen in transition metal compounds, such as hematite, iron manganese, and nickel oxide.
Ferrimagnetism: Like ferromagnets, ferrimagnets retain magnetization when removed from a magnetic field but neighboring pairs of electron spins point in opposite directions.
The lattice arrangement of the material makes the magnetic moment pointing in one direction stronger than that pointing in the other direction.
Ferrimagnetism occurs in magnetite and other ferrites.
Like ferromagnets, ferrimagnets are attracted to magnets.
There are other types of magnetism, too, including superparamagnetism, metamagnetism, and spin glass.
Properties of Magnets
Magnets form when ferromagnetic or ferrimagnetic materials are exposed to an electromagnetic field.
Magnets display certain characteristics:
There is a magnetic field surrounding a magnet.
Magnets attract ferromagnetic and ferrimagnetic materials and can turn them into magnets.
A magnet has two poles that repel like poles and attract opposite poles.
The north pole is repelled by north poles of other magnets and attracted to south poles.
The south pole is repelled by the south pole of another magnet but is attracted to its north pole.
Magnets always exist as dipoles.
In other words, you can't cut a magnet in half to separate north and south.
Cutting a magnet makes two smaller magnets, which each have north and south poles.
The north pole of a magnet is attracted to Earth's north magnetic pole, while the south pole of a magnet is attracted to Earth's south magnetic pole.
This can be kind of confusing if you stop to consider the magnetic poles of other planets.
For a compass to function, a planet's north pole is essentially the south pole if the world was a giant magnet!
Magnetism in Living Organisms
Some living organisms detect and use magnetic fields.
The ability to sense a magnetic field is called magnetoception.
Examples of creatures capable of magnetoception include bacteria, mollusks, arthropods, and birds.
The human eye contains a cryptochrome protein which may allow some degree of magnetoception in people.
Many creatures use magnetism, which is a process known as biomagnetism.
For example, chitons are mollusks that use magnetite to harden their teeth.
Humans also produce magnetite in tissue, which may affect the immune and nervous system functions.
Magnetism Key Takeaways
Magnetism arises from the electromagnetic force of a moving electric charge.
A magnet has an invisible magnetic field surrounding it and two ends called poles.
The north pole points toward Earth's north magnetic field.
The south pole points toward the Earth's south magnetic field.
The north pole of a magnet is attracted to the south pole of any other magnet and repelled by the north pole of another magnet.
Cutting a magnet forms two new magnets, each with north and south poles.
Magnetism exists in two forms, it exists in objects and in air.
1. Refrigerator magnets – artwork & messages :
A refrigerator magnet is a hard object, and more specifically a permanent magnet.
When this magnet is held in your hand, it has adapted to its present situation and rests in its lowest possible energy state.
If you now move this magnet toward the refrigerator door (which is a soft object) you have given the magnet a new environmental condition or situation.
The magnet will adapt itself in order to reach the new lowest possible energy state.
Specifically, it will do this by sending a portion of its’ energy into the refrigerator door which will absorb it.
This energy minimization process illustrates what was described above as attraction;
the refrigeration magnet will be attracted to the refrigerator door.
One can take advantage of this attractive force and use the magnet to hold artwork or messages to the door;
there will however be a limit to the weight which the magnet can support.
2. Refrigerator magnets – to seal and close the doors :
The refrigerator manufacturers use the knowledge described above to not only close the door when it gets reasonably close to the refrigerator frame but also to pull the door, which has a permanent magnet gasket along the inside edge, very snugly to the refrigerator frame.
This accomplishes two things;
it allows the owner the freedom to no slam the door closed, and it provides an extremely effective thermal seal.
3. Metal machine shop holding devices :
In a machine shop, it is paramount that pieces of metal be held firmly in place.
If this is accomplished, accidents and mistakes are less frequent and less damaging.
By utilizing the same knowledge from above, it is possible to produce attractive forces that are large enough to do two things.
One, the attractive forces are sufficient enough to hold a piece of metal heavier than the actual magnet itself, and two, the attractive forces are able to withstand additional forces created from the various machine operations.
A requirement of these attractive forces is that they can be turned on and off upon request.
This requires a clever diversion of the magnet energy away from the held metal.
4. Scrapyard and steel mill lifting :
In a scrap yard or steel mill, it is necessary to lift and relocate large quantities of metal.
As the metal is largely steel, it is a soft object.
With the knowledge mentioned earlier, magnetism is used to accomplish this task.
A very large crane using either an electromagnet or an assembly of hard magnetic objects on the end of its cable is able to pick up, relocate, and release the steel pieces.
5. Separation of materials :
Mines of various types use magnetism to separate the materials being collected. Attractive forces, similar to those described earlier, are placed near a conveyor transporting the mined materials.
As the soft magnetic objects move by the magnetic assembly they are drawn away from the conveyor containing the desired material and diverted to the collection area.
Various degrees of sophistication are available enabling the mine to be quite selective in their collection and separation of materials.
6. Radiation isotope creation :
Many forms of medical research utilize radiation in the form of isotopes.
These isotopes are used to isolate and observe various forms of medical problems;
diabetes, cancer, and AIDS are but a few examples.
Most of these isotopes are manufactured;
they are not abundant in their natural forms.
The knowledge presented above is actually used to produce these isotopes.
A device called an accelerator provides an element ( like phosphorus) with a tremendous amount of energy causing the element to change state and to emit radiation in order to minimize its energy.
7. Pure Physics research :
Subatomic Physics experiments utilize magnetism to create and observe the smallest structures of matter. Attractive and repulsive forces are generated by magnetism in controlled environmental chambers.
Responses are predicted for certain structures of matter under controlled circumstances.
Observation of the actual responses clarifies or disproves the predictions.
This enables society to gain a clearer understanding of what matter consists of, and better equips us to solve future problems.
8. Motors – automotive, lawnmower, kitchen mixer :
Motor manufacturers utilize the same knowledge from above to produce rotation in their motors.
A motor is divided into several wedge-shaped areas.
Synchronized electrical signals generate small attractive forces that rotate the motor from one wedge region to the next.
The speed of the motor is directly related to the rate at which the electrical signals are repeated.
9. Incontinence-bladder valve replacement :
Unfortunately, some people suffer an inability to urinate on demand;
this is a form of incontinence.
In an effort to assist these people, artificial bladder valves have been developed.
These valves are surgically implanted inside the individual.
The valve contains a fluid that contains quantities of a soft object dispersed uniformly throughout the fluid.
A permanent magnet producing an attractive force is then used to move the valve and open the urinary tract.
10. Dentures :
A new form of denture adhesion utilizes the knowledge from above.
Small pieces of the permanent magnet are surgically implanted in an individual’s gums, and pieces of soft objects are placed in selected portions of the denture.
When the denture is then put in place, adhesion results from the attraction.
11. Levitation of trains :
Magnetic repulsion is used to levitate trains.
One set of very strong dipoles (The train) experiences a repulsive force from another set of dipoles (The track).
As a result, the train moves as far away from the track as possible and is at least partially levitated.
This levitation reduces the resistance that the train experiences in order to move (friction).
The train will then require less fuel to move from one station to the next and can move at faster speeds as well.
12. Navigation via the compass :
Navigation using a compass is accomplished because the earth generates magnetism.
Geographically the top of the globe is labeled the ‘North Pole’, and the bottom the ‘South Pole’.
Currently the earth’s ‘North Pole’ is magnetically a south pole, and the earth’s ‘South Pole’ is magnetically a north pole.
A compass at location ‘A’ on Earth will point to the earth’s ‘North Pole’.
If we consider the attractive knowledge that we have learned from above it becomes apparent that the end of the compass labeled with an ‘N’ must be magnetically a north pole, and the end of the compass labeled with a ‘S’ must be magnetically a south pole.
This configuration for the compass allows it to minimize its energy pointing to the Earth’s ‘North Pole’, which of course provides our directional reference.
13. Store and library item security tags :
For security measures, it is necessary to determine whether an object (either a book in a library or a pair of jeans in a store) leaves a designated area without permission.
This monitoring can be done with magnetism.
As we have seen, a group of dipoles can have unique responses to their environment.
Some soft objects and some combinations of hard and soft objects in a mosaic pattern exhibit such unique responses, that they can be used as ‘tags’.
If a person leaves the designated area appropriately, the tag is neutralized or removed.
If they do not, then the ‘tag’ triggers the detection systems, and an alarm sounds notifying authorities of the problem.
14. Shark navigation :
Sharks navigate in the ocean in reference to the earth’s ‘North Pole’ and ‘South Pole’.
As they swim, they are regularly moving their heads from side to side.
It has been discovered that they have small sensing elements in their heads which convert the earth’s magnetic energy into electrical impulses.
These impulses are used by the shark to maintain a directional reference for navigation.
Nuclear magnetic resonance also occurs as a result of energy minimization.
Physicists long ago hypothesized a unique set of environmental conditions that would in effect cause a magnetic dipole to precess and then continually spin like a top (or resonate) in order to minimize its energy.
Free dipoles in the presence of the following unique environmental conditions will produce magnetic resonance;
a strong alignment applied field in a direction similar to twelve o’clock, and a pulsed (short duration) oscillating applied field is in the direction similar to three o’clock.
(see figure 8 ) The pulsed oscillating applied field is in the form of a sine function at a frequency somewhere in the radio frequency range (several million cycles per second).
Frequency determines how many times a function is repeated in a set amount of time.
The faster the frequency, the faster the function changes, and the more cycles which will have been produced.
Figure 8 : Applied Field Conditions for Magnetic Resonance
The outcome of the above-hypothesized experiment has provided us with an extremely important observation tool which is noninvasive;
this means that the material or object being observed is not altered or destroyed.
This technique is called Magnetic Resonance Imaging (MRI).
15. MRI for moisture & fat content analysis :
Magnetic resonance is used by food manufacturers (like Pepperidge Farm) to monitor and optimize the water and fat content in their ingredients in order to determine and maintain taste and shelf life.
Small amounts of materials are placed in a device that duplicates the above conditions.
The resonance response is monitored and directly correlated to either water or fat content.
This is accomplished because water and fat both contain magnetic dipoles and their response is different enough to be distinguished.
16. MRI for body & organ images :
Magnetic resonance is used to produce 3D images of the organs in the body with a clarity and a resolution exceeding that of the conventional x-ray and without the use of harmfully penetrating x-rays.
The production of, a useful image requires an even more special set of conditions than that described above.
The alignment of the applied field is still required, but this field now has two components, a uniform ‘field, and a gradient field. A uniform field is a field that has a magnitude over a volume like a 16-inch diameter sphere which differs from the average by only 30 or 40 parts per million (ppm), or alternatively by only .003 or.004 percent (%) anywhere in the sphere.
The gradient field is a field that changes linearly with distance from the center of the sphere as one move to the edge of the sphere.
This gradient field provides a means of determining spatial relations during the image production and thus is a major contributor to the increase in clarity and resolution that an MRI provides.
The uniform field and the gradient field are used simultaneously to align the dipoles in the observation region.
These dipoles minimize their energies by aligning with the field. Now the pulsed-field is introduced;
as described above the dipoles will resonate in order to best minimize their energies.
This resonance is monitored and recorded as an electrical impulse.
A sequence of different gradient fields will be applied covering the entire organ area of interest.
Once all of the data has been collected (this takes close to one hour) it is processed by a powerful computer to produce the 3D image.
17. Transmission Line transformers :
Soft magnetic objects are used by the power companies.
The large transformers (both residential and industrial) convert energy from one form into the energy of another form.
Specifically, they transform voltage at one magnitude into a voltage of 110 or 220 volts, which are the typical household appliance voltages.
Transmission lines contain several thousand volts, and a transformer containing soft magnetic objects is used to turn this large amplitude of voltage into the 110 and 220 volts used in your house.
18. Recording heads – VCR, audio & video cassettes, hard & floppy disk drives :
A special coding sequence is used to accomplish information storage.
This coding sequence requires that energy (in the form of applied fields) be presented to storage media in small organized areas. Soft magnetic objects are used to channel this magnetic energy into appropriate locations in order to accomplish the information storage.
19. Recording media- VCR, audio & video cassettes, hard & floppy disk drives :
As mentioned previously, recording media is a hard magnetic object.
These forms of media are used extensively in our everyday lives either directly or indirectly.
The desired information is saved to the magnetic material for our retrieval later.
We are also able to record and re-record as we desire with no degradation in performance or capabilities.
20. Credit cards & ATM bank cards :
Most credit cards contain a strip of the hard magnetic object on the back of the card.
This strip contains coded information;
specifically, your name(s), account number(s), and probably a few other special items.
When you make a purchase with a credit card it is now rare for the clerk to have to talk to anyone to clarify your ability to purchase an item.
Instead, the clerk will pass your card through a small box.
This box is an intelligent interface between the store and the credit card office.
Your credit card information is read off of your card by the small box and is then directly passed to the credit card computer via a telephone line.
The clerk then will enter your purchase amount, and wait for an approval number.
If you use an automatic teller machine (ATM), the ATM will access your account information from your card and then will prompt you to initiate bank transactions.
Any of your selections are computer-controlled and fully automated and all initiated by magnetics.
Which Metals Are Magnetic?
Magnets were first discovered by ancient civilizations going back 2,500 years, and by the 12th and 13th centuries AD, magnetic compasses were commonly used for navigation in China and Europe.
Today, magnets are an essential part of modern technology.
They are found in almost any appliance you can name, from mobile phone speakers to electric motors, washing machines, and air conditioners.
The magnet industry continues to grow due to the increased demand for magnetic circuit components widely used in industrial equipment, while technological advances enable magnets to be 60 times as strong as they were 90 years ago.
Which Metals Are Magnetic?
Some alloys of rare earth metals
These magnetic metals fall under the categories: Permanent Magnets Neodymium Magnets
When people think of magnets, they’re often thinking of permanent magnets.
These are objects which can be magnetized to create a magnetic field.
The most common example is the refrigerator magnet, used to hold notes on our refrigerator door.
The most common metals used for permanent magnets are iron, nickel, cobalt and some alloys of rare-earth metals.
There are two types of permanent magnets: those from “hard” magnetic materials and those from “soft” magnetic materials. “Hard” magnetic metals tend to stay magnetized over a long period.
Common examples are:
Alnico alloy, an iron alloy with aluminum, nickel, and cobalt.
Alnico alloys make strong permanent magnets.
They are widely used in industrial and consumer electronics.
For example, in large electric motors, microphones, loudspeakers, electric guitar pickups and microwaves.
Ferrite, a ceramic compound composed of iron oxide and other metallic elements.
Ferrites are used in refrigerator magnets and small electric motors.
“Soft” magnetic metals can be magnetized but lose their magnetism quickly.
Common examples are iron-silicon alloys and nickel-iron alloys.
These materials are typically used in electronics, for example, transformers and magnetic shielding.
Electromagnets are made from a coil of copper wire wound around a core made from iron, nickel or cobalt.
The coiled wire will generate a magnetic field when an electric current passes through it, however, the magnetic field disappears the moment the current stops.
Electromagnets need electricity to work.
Their usefulness lies in the ability to vary the strength of the magnetic field through controlling the electrical current in the wire.
Electromagnets are commonly used in electric motors and generators.
They both work on the scientific principle of electromagnetic induction, discovered by scientist Michael Faraday in 1831, which says that a moving electric current will create a magnetic field, and vice versa.
In electric motors, the electric current generates a magnetic field that moves the motor.
In generators, an external force such as wind, flowing water or steam rotates a shaft which moves a set of magnets around a coiled wire, thus producing an electric current.
Electromagnets are also used to flick the switches in relays, used in telephone exchanges, railway signaling and traffic lights.
Junkyard cranes are also fitted with electromagnets which are used to pick up and drop large vehicles with ease.
These electromagnets take the form of a round plate fitted to the end of the crane.
A modern train system known as Maglev (short for magnetic levitation) uses electromagnets to levitate the train above the rail.
This reduces friction and allows the train to move at tremendous speed.
Advanced applications of electromagnets include magnetic resonance imaging (MRI) machines, and particle accelerators (like the Large Hadron Collider).
Neodymium magnets are a type of rare-earth magnet comprised of an alloy of neodymium, iron, and boron.
They were devised in 1982 by General Motors and Sumitomo Special Metals.
Neodymium magnets are the strongest type of permanent magnet commercially available.
They are used when strong permanent magnets are required, particularly in cordless tool motors, hard disk drives and magnetic fasteners.
Turning Non-Magnetic Metals Into Magnets
Copper and manganese are not normally magnetic.
However, a ground-breaking new technique, developed by Oscar Cespedes of the University of Leeds, UK, has transformed copper and manganese into magnets.
Cespedes and his team fabricated films of copper and manganese on carbon structures called Buckyballs.
When an external magnetic field was applied and removed, the films retained 10% of the magnetic field.
This new technique is set to provide a more biocompatible and environmentally-friendly way to manufacture MRI machines.
Other possible applications include use in wind turbines.
Wind turbines currently use iron cobalt and nickel with rare-Earth elements.
But these elements are expensive and tough to mine.
The breakthrough opens the possibilities to cheaper alternatives.
Only a few materials, called "ferromagnetic" materials, exhibit magnetic properties of significant strength.
These materials include nickel, iron, cobalt, a few rare earth elements, and some of their alloys.
These materials can become magnetized when exposed to an external magnetic field, and consequently attracted to a magnet.
In this case, magnetic domains within the material become temporarily aligned to create a magnetic field of their own.
Some of these materials may remain in their aligned state even when the external field is removed, thereby making a permanent magnet.
See our lesson on Iron and Magnets for more discussion about the microscopic process of magnetization.
Table 1 shows a list of some common metals, their magnetic properties, and where they might be found.
A good exercise for students is to try to identify all the magnetic and non-magnetic metals in the area using a magnet.
Have them try to identify each metal they come across.
One student can act as a scribe to keep track of the discoveries on the blackboard, or each student can fill out their own checklist of common metals (attached).
More advanced students may try to measure the strength of the magnetic force by recording the distance at which it just cancels the weight of the magnet (i.e. the distance at which the magnet just lifts off the table).
Everyone has played with magnets, but not everyone understands how they work.
This lesson will explain how magnets work and will take a closer look at how three different types of substances--ferromagnetic, paramagnetic, and diamagnetic--react to magnetic fields.
Background on Magnets
Magnets probably play a bigger role in your life than you think.
Sure, you see magnets on your refrigerator, but did you know that the speakers in your TV, your car's automatic door locks, and your washing machine contain magnets? In fact, even the earth is a magnet! Of course, you probably have a general idea of what a magnet is, but have you actually thought about how a magnet works, or why some materials are magnetic and others are not? If not, don't worry, you've come to the right place!
A good start would be to define some words associated with magnets.
Magnetism is the result of attraction, when two objects come together, or repulsion when two objects move apart.
A magnet is an object that has properties of magnetism.
For example, a magnet might attract another object.
A magnetic field is an invisible area around a magnet where magnetism occurs.
And magnetized means that an object acquired magnetic properties.
Now, some substances can be super magnetic and others can be partially magnetic.
Let's take a look at three different types of substances: ferromagnetic, paramagnetic, and diamagnetic.
Let's start with ferromagnetic substances.
Ferromagnetic substances get their name because the word for iron in Latin is 'ferrum' and iron is one of the ferromagnetic substances.
Other substances that fall into this group include cobalt, nickel, and gadolinium.
So, what makes something 'ferromagnetic?'
Everything around you, from your dog to your TV, is made up of atoms.
In the center, or nucleus, of the atom are protons and neutrons, while electrons are spinning around outside of the nucleus.
The electrons are outside of the nucleus
You can think of electrons as tiny spinning magnets.
Normally, one electron spins one way and another spins the other way, canceling each other out so the atom doesn't have any magnetic properties.
But in a ferromagnetic substance, the electrons will orient themselves to spin the same way when they are exposed to a magnetic field, thus magnetizing the ferromagnetic substance.
Check out the images below:
The electron orientation is represented by arrows.
The electrons all orient in the same way after the material is exposed to a magnetic field
You'll see that the electron orientation is represented by arrows.
The electrons all orient in the same way after the material is exposed to a magnetic field.
Picture some iron that gets placed next to a bar magnet.
The magnetic field in the bar magnet causes the electrons in the iron to orient themselves the same way and thus, makes the iron magnetic!
And what's even cooler is that ferromagnetic substances, like that chunk of iron, will remain magnetized even after that bar magnet is long gone.
Paramagnetic substances are still pretty neat, even if they don't stay magnetized like the ferromagnetic substances.
They are only magnetized briefly when exposed to a magnetic substance.
Some examples of paramagnetic substances include aluminum, platinum, titanium, and tin.
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