What is a Magnetic Field?

Everyone knows just how fun magnets can be. As a child, who among us didn’t love to see if we could make our silverware stick together? And how about those little magnetic rocks that we could arrange to form just about any shape because they stuck together? Well, magnetism is not just an endless source of fun or good for scientific experiments; it’s also one of basic physical laws upon which the universe is based.

The attraction known as magnetism occurs when a magnetic field is present, which is a field of force produced by a magnetic object or particle. It can also be produced by a changing electric field and is detected by the force it exerts on other magnetic materials. Hence why the area of study dealing with magnets is known as electromagnetism.

Definition:

Magnetic fields can be defined in a number of ways, depending on the context. However, in general terms, it is an invisible field that exerts magnetic force on substances which are sensitive to magnetism. Magnets also exert forces and torques on each other through the magnetic fields they create.

Visualization of the solar wind encountering Earth's magnetic "defenses" known as the magnetosphere. Clouds of southward-pointing plasma are able to peel back layers of the Sun-facing bubble and stack them into layers on the planet's nightside (center, right). The layers can be squeezed tightly enough to reconnect and deliver solar electrons (yellow sparkles) directly into the upper atmosphere to create the aurora. Credit: JPL
Visualization of the solar wind encountering Earth’s magnetosphere. Like a dipole magnet, it has field lines and a northern and southern pole. Credit: JPL

They can be generated within the vicinity of a magnet, by an electric current, or a changing electrical field. They are dipolar in nature, which means that they have both a north and south magnetic pole. The Standard International (SI) unit used to measure magnetic fields is the Tesla, while smaller magnetic fields are measured in terms of Gauss (1 Tesla = 10,000 Guass).

Mathematically, a magnetic field is defined in terms of the amount of force it exerted on a moving charge. The measurement of this force is consistent with the Lorentz Force Law, which can be expressed as F= qvB, where F is the magnetic force, q is the charge, v is the velocity, and the magnetic field is B. This relationship is a vector product, where F is perpendicular (->) to all other values.

Field Lines:

Magnetic fields may be represented by continuous lines of force (or magnetic flux) that emerge from north-seeking magnetic poles and enter south-seeking poles. The density of the lines indicate the magnitude of the field, being more concentrated at the poles (where the field is strong) and fanning out and weakening the farther they get from the poles.

A uniform magnetic field is represented by equally-spaced, parallel straight lines. These lines are continuous, forming closed loops that run from north to south, and looping around again. The direction of the magnetic field at any point is parallel to the direction of nearby field lines, and the local density of field lines can be made proportional to its strength.

Magnetic field lines resemble a fluid flow, in that they are streamlined and continuous, and more (or fewer lines) appear depending on how closely a field is observed. Field lines are useful as a representation of magnetic fields, allowing for many laws of magnetism (and electromagnetism) to be simplified and expressed in mathematical terms.

A simple way to observe a magnetic field is to place iron filings around an iron magnet. The arrangements of these filings will then correspond to the field lines, forming streaks that connect at the poles. They also appear during polar auroras, in which visible streaks of light line up with the local direction of the Earth’s magnetic field.

History of Study:

The study of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field of a spherical magnet using iron needles. The places where these lines crossed he named “poles” (in reference to Earth’s poles), which he would go on to claim that all magnets possessed.

During the 16th century, English physicist and natural philosopher William Gilbert of Colchester replicated Peregrinus’ experiment. In 1600, he published his findings in a treaties (De Magnete) in which he stated that the Earth is a magnet. His work was intrinsic to establishing magnetism as a science.

View of the eastern sky during the peak of this morning's aurora. Credit: Bob King
View of the eastern sky during the peak of this morning’s aurora. Credit: Bob King

In 1750, English clergyman and philosopher John Michell stated that magnetic poles attract and repel each other. The force with which they do this, he observed, is inversely proportional to the square of the distance, otherwise known as the inverse square law.

In 1785, French physicist Charles-Augustin de Coulomb experimentally verified Earths’ magnetic field. This was followed by 19th century French mathematician and geometer Simeon Denis Poisson created the first model of the magnetic field, which he presented in 1824.

By the 19th century, further revelations refined and challenged previously-held notions. For example, in 1819, Danish physicist and chemist Hans Christian Orsted discovered that an electric current creates a magnetic field around it. In 1825, André-Marie Ampère proposed a model of magnetism where this force was due to perpetually flowing loops of current, instead of the dipoles of magnetic charge.

In 1831, English scientist Michael Faraday showed that a changing magnetic field generates an encircling electric field. In effect, he discovered electromagnetic induction, which was characterized by Faraday’s law of induction (aka. Faraday’s Law).

A Faraday cage in power plant in Heimbach, Germany. Credit: Wikipedia Commons/Frank Vincentz
A Faraday cage in power plant in Heimbach, Germany. Credit: Wikipedia Commons/Frank Vincentz

Between 1861 and 1865, Scottish scientist James Clerk Maxwell published his theories on electricity and magnetism – known as the Maxwell’s Equations. These equations not only pointed to the interrelationship between electricity and magnetism, but showed how light itself is an electromagnetic wave.

The field of electrodynamics was extended further during the late 19th and 20th centuries. For instance, Albert Einstein (who proposed the Law of Special Relativity in 1905), showed that electric and magnetic fields are part of the same phenomena viewed from different reference frames. The emergence of quantum mechanics also led to the development of quantum electrodynamics (QED).

Examples:

A classic example of a magnetic field is the field created by an iron magnet. As previously mentioned, the magnetic field can be illustrated by surrounding it with iron filings, which will be attracted to its field lines and form in a looping formation around the poles.

Larger examples of magnetic fields include the Earth’s magnetic field, which resembles the field produced by a simple bar magnet. This field is believed to be the result of movement in the Earth’s core, which is divided between a solid inner core and molten outer core which rotates in the opposite direction of Earth. This creates a dynamo effect, which is believed to power Earth’s magnetic field (aka. magnetosphere).

Computer simulation of the Earth's field in a period of normal polarity between reversals.[1] The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth's core
Computer simulation of the Earth’s field in a period of normal polarity between reversals.[1] The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. Credit: NASA
Such a field is called a dipole field because it has two poles – north and south, located at either end of the magnet – where the strength of the field is at its maximum. At the midpoint between the poles the strength is half of its polar value, and extends tens of thousands of kilometers into space, forming the Earth’s magnetosphere.

Other celestial bodies have been shown to have magnetic fields of their own. This includes the gas and ice giants of the Solar System – Jupiter, Saturn, Uranus and Neptune. Jupiter’s magnetic field is 14 times as powerful as that of Earth, making it the strongest magnetic field of any planetary body. Jupiter’s moon Ganymede also has a magnetic field, and is the only moon in the Solar System known to have one.

Mars is believed to have once had a magnetic field similar to Earth’s, which was also the result of a dynamo effect in its interior. However, due to either a massive collision, or rapid cooling in its interior, Mars lost its magnetic field billions of years ago. It is because of this that Mars is believed to have lost most of its atmosphere, and the ability to maintain liquid water on its surface.

When it comes down to it, electromagnetism is a fundamental part of our Universe, right up there with nuclear forces and gravity. Understanding how it works, and where magnetic fields occur, is not only key to understanding how the Universe came to be, but may also help us to find life beyond Earth someday.

We have written many articles about the magnetic field for Universe Today. Here’s What is Earth’s Magnetic Field, Is Earth’s Magnetic Field Ready to Flip?, How Do Magnets Work?, Mapping The Milky Way’s Magnetic Fields – The Faraday Sky, Magnetic Fields in Spiral Galaxies – Explained at Last?, Astronomy Without A Telescope – Cosmic Magnetic Fields.

If you’d like more info on Earth’s magnetic field, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:

Minute Physics: Real World Telekinesis

How do magnets affect things at a distance? How does the Sun heat our planet from 93 million miles away? How can we send messages across the world with our cell phones? We take these seemingly simple things for granted, but in fact there was a time not too long ago when the processes behind them were poorly understood, if at all… and, to the uninformed, there could seem to be a certain sense of “magic” about them.

This video from MinutePhysics, featuring director of the Perimeter Institute for Theoretical Physics Neil Turok, illustrates how our understanding of electromagnetic fields was developed and why there’s nothing magic about it… except, perhaps, how they pack all that excellent info into 5 minutes. Enjoy!

Video: MinutePhysics (Created by Henry Reich.) In conjunction with The CBC Massey Lectures.

An Anti-Gravity User Interface

Researcher Jinha Lee at MIT has developed a remarkable way to interact with computers — via a programmable, intelligent and gravity-defying metal ball.

The concept, called “ZeroN”, is demonstrated in the video above. Fascinating!

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Using magnets and computer-controlled motors, ZeroN hovers in mid-air between two control units. Its movements can be pre-programmed or it can react to objects in its environment, and it can apparently “learn” new movements as it is interacted with.

Lee demonstrates how it could be used to control camera positions in 3D applications, and (my favorite) model the motions of planets and stars.

“ZeroN is about liberating materials from the constraints of space and time by blending the physical and digital world,” Lee states on his website.

ZeroN is still in its development stages and obviously needs refining (the 3D camera isn’t much use if the ball is wobbling) but the premise is interesting. I can see something like this being, at the very least, a mesmerizing interactive display for museums, classrooms and multimedia presentations.

Of course, with a little ingenuity a whole world of applications could open up for such a zero-g interface. (I’m sure Tony Stark already has a dozen on pre-order!)

Read more about this on Co.DESIGN (tip of the electromagnetic hat to PopSci.)

Are Pulsars Giant Permanent Magnets?

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Some of the most bizarre phenomena in the universe are neutron stars. Very few things in our universe can rival the density in these remnants of supernova explosions. Neutron stars emit intense radiation from their magnetic poles, and when a neutron star is aligned such that these “beams” of radiation point in Earth’s direction, we can detect the pulses, and refer to said neutron star as a pulsar.

What has been a mystery so far, is how exactly the magnetic fields of pulsars form and behave. Researchers had believed that the magnetic fields form from the rotation of charged particles, and as such should align with the rotational axis of the neutron star. Based on observational data, researchers know this is not the case.

Seeking to unravel this mystery, Johan Hansson and Anna Ponga (Lulea University of Technology, Sweden) have written a paper which outlines a new theory on how the magnetic fields of neutron stars form. Hansson and Ponga theorize that not only can the movement of charged particles form a magnetic field, but also the alignment of the magnetic fields of components that make up the neutron star – similar to the process of forming ferromagnets.

Getting into the physics of Hansson and Ponga’s paper, they suggest that when a neutron star forms, neutron magnetic moments become aligned. The alignment is thought to occur due to it being the lowest energy configuration of the nuclear forces. Basically, once the alignment occurs, the magnetic field of a neutron star is locked in place. This phenomenon essentially makes a neutron star into a giant permanent magnet, something Hansson and Ponga call a “neutromagnet”.

Similar to its smaller permanent magnet cousins, a neutromagnet would be extremely stable. The magnetic field of a neutromagnet is thought to align with the original magnetic field of the “parent” star, which appears to act as a catalyst. What is even more interesting is that the original magnetic field isn’t required to be in the same direction as the spin axis.

One more interesting fact is that with all neutron stars having nearly the same mass, Hansson and Ponga can calculate the strength of the magnetic fields the neutromagnets should generate. Based on their calculations, the strength is about 1012 Tesla’s – almost exactly the observed value detected around the most intense magnetic fields around neutron stars. The team’s calculations appear to solve several unsolved problems regarding pulsars.

Hansson and Ponga’s theory is simple to test – since they state the magnetic field strength of neutron stars cannot exceed 1012 Tesla’s. If a neutron star were to be discovered with a stronger magnetic field than 1012 Tesla’s, the team’s theory would be proven wrong.

Due to the Pauli exclusion principle possibly excluding neutrons aligning in the manner outlined in Hansson and Ponga’s paper, there are some questions regarding the team’s theory. Hansson and Ponga point to experiments that have been performed which suggest that nuclear spins can become ordered, like ferromagnets, stating: “One should remember that the nuclear physics at these extreme circumstances and densities is not known a priori, so several unexpected properties might apply,”

While Hansson and Ponga readily agree their theories are purely speculative, they feel their theory is worth pursuing in more detail.

If you’d like to learn more, you can read the full scientific paper by Hansson & Pong at: http://arxiv.org/pdf/1111.3434v1

Source: Pulsars: Cosmic Permanent ‘Neutromagnets’ (Hansson & Pong)

Paramagnetism

Paramagnetism

[/caption]Magnetism is a fundamental force of the universe, essential to its function and existence in the same way that gravity and weak and strong nuclear forces are. But interestingly enough, there are several different kinds of magnetism. For example, there is ferromagnetism, a property which applies to super magnets, where magnetic properties exist regardless of whether or not there is a magnetic field acting on the material itself. There is also Diamagnetism, which refers to materials that are not affected by a magnetic field, and Paramagnetism, a form of magnetism that occurs only in the presence of an externally applied magnetic field.

Materials that are called ‘paramagnets’ are most often those that exhibit, at least over an appreciable temperature range, magnetic susceptibilities that adhere to the Curie or Curie–Weiss laws. According to these laws, which apply at low-levels of magnetization, the susceptibility of paramagnetic materials is inversely proportional to their temperature. Mathematically, this can be expressed as: M = C(B/T), where M is the resulting magnetization, B is the magnetic field, T is absolute temperature, measured in kelvins, C is a material-specific Curie constant.

Paramagnets were named and extensively researched by British scientist Michael Faraday – the man who gave us Faraday’s Constant, Faraday’s Law, the Faraday Effect, etc. – beginning in 1845. He, and many scientists since, found that certain material exhibited what was commonly referred to as “negative magnetism”. Most elements and some compounds are paramagnetic, with strong paramagnetism being exhibited by compounds containing iron, palladium, platinum, and certain rare-earth elements. In such compounds atoms of these elements have some inner electron shells that are incomplete, causing their unpaired electrons to spin like tops and orbit like satellites. This makes the atoms act like a permanent magnet, tending to align with and hence strengthen an applied magnetic field. However, once the magnetic field is removed, the atoms fall out of alignment and the material return to its original state. Strong paramagnetism also decreases with rising temperature because of the de-alignment produced by the greater random motion of the atomic magnets.

Weak paramagnetism, independent of temperature, is found in many metallic elements in the solid state, such as sodium and the other alkali metals. Other examples include Iron oxide, Uranium, Platinum, Tungsten, Cesium, Aluminum, Lithium, Magnesium, Sodium, and Oxygen gas. Even iron, a highly magnetic material, can become a paramagnet once it is heated above its relatively high Curie-point.

We have written many articles about magnetism for Universe Today. Here’s an article about magnetic field, and here’s an article about what magnets are made of.

If you’d like more info on paramagnetism, check out these articles from Hyperphysics and Physlink.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
http://en.wikipedia.org/wiki/Paramagnetism
http://en.wikipedia.org/wiki/Faraday
http://www.britannica.com/EBchecked/topic/442927/paramagnetism
http://www.physlink.com/education/askexperts/ae595.cfm
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

Magnetic Energy

Magnetic Energy

[/caption]During the 19th century, one of the greatest discoveries in the history of physics was made by an Scottish physicist named James Clerk Maxwell. It was at this time, while studying the perplexing nature of magnetism and electricity, that he proposed a radical new theory. Electricity and magnetism, long thought to be separate forces, were in actuality closely associated with each other. That is, every electrical current has associated with it a magnetic field and every changing magnetic field creates its own electrical current. Maxwell went on to express this in a set of partial differential equations, known as Maxwell’s Equations, and form the basis for both electrical and Magnetic Energy.

In fact, thanks to Maxwell’s work, magnetic and electric energy are more appropriately considered as a single force. Together, they are what is known as electromagnetic energy – i.e. a form of energy that has both electrical and magnetic components. It is created when one runs a magnetic current through a wire or any other conducive material, creating a magnetic field. The magnetic energy generated can be used to attract other metal parts (as in the case in many modern machines that have moving parts) or can be used to generate electricity and store power (hydroelectric dams and batteries).

Since the 19th century, scientists have gone on to understand that many types of energy are in fact forms of electromagnetic energy. These include x rays, gamma rays, visible light (i.e. photons), ultraviolet light, infrared radiation, radio waves, and microwaves. These forms of electromagnetic energy differ from each other only in terms of the wavelength and frequency. Those forms which have shorter waves and higher frequencies tend to be the more harmful varieties, such as x-rays and gamma rays, while those that have longer waves and shorter frequencies, such as radio waves, tend to be more benign.

In mathematical terms, the equation for measuring the output of a magnetic field can be expressed as follows: V = L dI/dt + RI where V is volume, L is inductance, R is resistance, I is charge, dI represents change in charge, and dt represents change over time.

Here are some articles about Magnetic Energy written for Universe Today.
Behind the Power and Beauty of Northern Lights
Magnetic Fields in Inter-cluster Space: Measured at Last

If you’d like more info on Magnetic Energy, check out these articles:
Wikipedia Entry on Magnetic Energy
More info about magnetic energy

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
http://en.wikipedia.org/wiki/Magnetic_energy
http://en.wikipedia.org/wiki/James_Clerk_Maxwell
http://en.wikipedia.org/wiki/Maxwell%27s_equations
http://fi.edu/guide/hughes/10types/typesmagnetic.html
http://farside.ph.utexas.edu/teaching/em/lectures/node84.html
http://science.jrank.org/pages/2489/Energy-Magnetic-energy.html

How Do Magnets Work

How Do Magnets Work

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We have all played with magnets from time to time. Every time you do, you have asked yourself ‘how do magnets work?’ Many of us understand that magnets have two different charges and that like charges repel each other, but that still does not explain how a magnet works. Below is an attempt to explain the basics behind the secret inner workings of the mysterious magnet.

A magnet is any material or object that produces a magnetic field. This magnetic field is responsible for the property of a magnet: a force that pulls on other ferromagnetic materials and attracts or repels other magnets. A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. Materials that can be magnetized, which are strongly attracted to a magnet, are called ferromagnetic. Although ferromagnetic materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field.

Some facts about magnets include:

  • the north pole of the magnet points to the geomagnetic north pole (a south magnetic pole) located in Canada above the Arctic Circle.
  • north poles repel north poles
  • south poles repel south poles
  • north poles attract south poles
  • south poles attract north poles
  • the force of attraction or repulsion varies inversely with the distance squared
  • the strength of a magnet varies at different locations on the magnet
  • magnets are strongest at their poles
  • magnets strongly attract steel, iron, nickel, cobalt, gadolinium
  • magnets slightly attract liquid oxygen and other materials
  • magnets slightly repel water, carbon and boron

The mechanics of how do magnets work really breaks right down to the atomic level. When current flows in a wire a magnetic field is created around the wire. Current is simply a bunch of moving electrons, and moving electrons make a magnetic field. This is how electromagnets are made to work.

Around the nucleus of the atom there are electrons. Scientists used to think that they had circular orbits, but have discovered that things are much more complicated. Actually, the patterns of the electron within one of these orbitals takes into account Schroedinger’s wave equations. Electrons occupy certain shells that surround the nucleus of the atom. These shells have been given letter names K,L,M,N,O,P,Q. They have also been given number names, such as 1,2,3,4,5,6,7(think quantum mechanics). Within the shell, there may exist subshells or orbitals, with letter names such as s,p,d,f. Some of these orbitals look like spheres, some like an hourglass, still others like beads. The K shell contains an s orbital called a 1s orbital. The L shell contains an s and p orbital called a 2s and 2p orbital. The M shell contains an s, p and d orbital called a 3s, 3p and 3d orbital. The N, O, P and Q shells each contain an s, p, d and f orbital called a 4s, 4p, 4d, 4f, 5s, 5p, 5d, 5f, 6s, 6p, 6d, 6f, 7s, 7p, 7d and 7f orbital. These orbitals also have various sub-orbitals. Each can only contain a certain number of electrons. A maximum of 2 electrons can occupy a sub-orbital where one has a spin of up, the other has a spin of down. There can not be two electrons with spin up in the same sub-orbital(the Pauli exclusion principal). Also, when you have a pair of electrons in a sub-orbital, their combined magnetic fields will cancel each other out. If you are confuse, you are not alone. Many people get lost here and just wonder about magnets instead of researching further.

When you look at the ferromagnetic metals it is hard to see why they are so different form the elements next to them on the periodic table. It is generally accepted that ferromagnetic elements have large magnetic moments because of un-paired electrons in their outer orbitals. The spin of the electron is also thought to create a minute magnetic field. These fields have a compounding effect, so when you get a bunch of these fields together, they add up to bigger fields.

To wrap things up on ‘how do magnets work?’, the atoms of ferromagnetic materials tend to have their own magnetic field created by the electrons that orbit them. Small groups of atoms tend to orient themselves in the same direction. Each of these groups is called a magnetic domain. Each domain has its own north pole and south pole. When a piece of iron is not magnetized the domains will not be pointing in the same direction, but will be pointing in random directions canceling each other out and preventing the iron from having a north or south pole or being a magnet. If you introduce current(magnetic field), the domains will start to line up with the external magnetic field. The more current applied, the higher the number of aligned domains. As the external magnetic field becomes stronger, more and more of the domains will line up with it. There will be a point where all of the domains within the iron are aligned with the external magnetic field(saturation), no matter how much stronger the magnetic field is made. After the external magnetic field is removed, soft magnetic materials will revert to randomly oriented domains; however, hard magnetic materials will keep most of their domains aligned, creating a strong permanent magnet. So, there you have it.

We have written many articles about magnets for Universe Today. Here’s an article about bar magnets, and here’s an article about super magnets.

If you’d like more info on magnets, check out some cool experiments with magnets, and here’s a link to an article about super magnets by Wise Geek.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
Wise Geek
Wikipedia: Magnet
Wikipedia: Ferromagnetism

Super Magnets

Permanent Magnet

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Magnets are not only a source of endless fun – for children and children of all ages! They also happen to have endless industrial applications. But when it comes to the high-tech industry, the people who rely on magnetic materials to build appliances, electronics, or even spaceships, only one type of magnet will do. These are known as Rare Earth or Super Magnets, the kind that are used in MRI machines, computer hard drives, electric and hybrid motors, audio speakers, electric guitars, and race car engines. In spite of their name, the elements used to make super magnets are actually quite common, but were rarely found in large enough quantities to be considered economically viable. However, since the 90’s these magnets have become cheap and widely available, and are even being considered for additional processes.

The term super magnet is a broad term and encompasses several families of rare-earth magnets that include seventeen elements in the periodic table; namely scandium, yttrium, and the fifteen lanthanides. First developed in the 1970’s and 80’s, super magnets are the strongest type of permanent magnets ever made, are ferromagnetic, meaning that like iron they can be magnetized, and have Curie temperatures that are below room temperature. This means that in their pure form, their magnetism only appears at low temperatures. However, since they can form compounds with transition metals such as iron, nickel, and cobalt, metals that have Curie temperatures well above room temperature, they can be used effectively at higher temperatures as well. The main advantage they have over conventional magnets is that their greater strength allows for smaller, lighter magnets to be used, ones that can do the same job but take up less space and require less material.

Super magnets can be broken down into two categories. First, there is the neodymium magnet, which is made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. This material is currently the strongest known type of permanent magnet and was developed in the 1980’s. It is typically used in the construction of head actuators in computer hard drives and has many electronic applications, such as electric motors, appliances, and magnetic resonance imaging (MRI). The second type of super magnet is the samarium-cobalt variety, an alloy of samarium and cobalt with the chemical formula of SmCo5. This second-strongest type of rare Earth magnet is also used in electronic motors, turbomachinery, and because of its high temperature range tolerance may also have many applications for space travel, such as cryogenics and heat resistant machinery.

We have written many articles about magnets for Universe Today. Here’s an article about where to buy magnets, and here’s an article about what magnets are made of.

If you’d like more info on Super Magnets, check out Rare Earth Magnetics Homepage, and here’s a link to Wikipedia: Rare Earth Magnets.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
http://en.wikipedia.org/wiki/Rare-earth_magnet
http://en.wikipedia.org/wiki/Magnet
http://en.wikipedia.org/wiki/Samarium-cobalt_magnet
http://en.wikipedia.org/wiki/Neodymium_magnet
http://www.newton.dep.anl.gov/askasci/phy99/phy99010.htm

Rare Earth Magnets

Permanent Magnet

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Magnets are an endless source of fun, not to mention a convenience when it comes to fridge notes and white boards! But when it comes to industrial uses, such as those used by the air force and NASA, only one type of magnet makes the grade. These are called Rare Earth Magnets, a set of strong permanent magnets made from the alloys of particular earth elements. These elements fall into the category of rare earth elements (or metals), which are a collection of seventeen elements in the periodic table; namely scandium, yttrium, and the fifteen lanthanides. Despite their name, rare earth elements are actually quite abundant, but are so named because of their geochemical properties, they are rarely found in economically exploitable concentrations.

Rare earth elements are ferromagnetic, meaning that like iron, they can be magnetized. However, because most rare earth elements have low Curie temperatures (the temperature at which they exhibit magnetic properties), meaning they are only magnetic at low temperatures. However, most form compounds with transition metals like iron, nickel and cobalt, which have higher Curie temperatures, and can therefore be mixed with them to enhance their natural magnetic properties. There are two types: neodymium magnets and samarium-cobalt magnets. The former, invented in the 1980s, are the strongest and most affordable type of rare-earth magnet, is made of neodymium, iron and boron (chemical formula: Nd2Fe14B). On the other hand, Samarium-cobalt magnets (chemical formula: SmCo5), the first family of rare earth magnets invented, are less used than neodymium magnets because of their higher cost and weaker magnetic field strength. However, samarium-cobalt has a higher Curie temperature, creating a niche for these magnets in applications where high field strength is needed at higher operating temperatures.

Neodymium magnets are typically used in most computer hard drives and a variety of audio speakers. They are also have a number of important medical applications, not the least of which involves magnetic resonance imaging (or MRI) technology. They are also part of the driving mechanisms for electrical and hybrid motors, servomotors, cordless tools, and power steering controls. Samarium-cobalt motors are commonly used in the construction of electrical guitars, high-end Slotcar racing engines, and turbomachinery. In addition, rare earth elements are being used as a catalysts in the petroleum cracking industry and to make auto emissions equipment, and may have many future applications for green technology. Samarium-cobalt magnets may also be used in the making of cryogenic and high-temperature systems for future space travel.

Originally, the high cost of these magnets limited their use to applications requiring compactness together with high field strength, but beginning in the 1990s, rare earth magnets have become steadily less expensive, and the low cost has inspired new uses (such as magnetic toys for children).

We have written many articles about magnets for Universe Today. Here’s an article about where to buy magnets, and here’s an article about what magnets are made of.

If you’d like more info on Rare Earth Magnets, check out Rare Earth Magnetics Homepage, and here’s a link to Wikipedia: Rare Earth Magnets.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
http://en.wikipedia.org/wiki/Rare_earth_element
http://en.wikipedia.org/wiki/Curie_temperature
http://blogs.wsj.com/chinarealtime/2010/11/02/video-how-a-rare-earth-magnet-works/
http://en.wikipedia.org/wiki/Rare-earth_magnet
http://en.wikipedia.org/wiki/Neodymium_magnet
http://en.wikipedia.org/wiki/Samarium-cobalt

What are Magnets Made Of

Magnet

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Magnets are the unsung heroes of the Modern Age. However most people don’t really understand what are magnets made of and how they even work. The issue is that we just know that magnets attract iron and nickel. However, magnets have a very interesting origin and can be seen as a physical manifestation of the electromagnetic force.

All magnets are made of a group of metals called the ferromagnetic metals. These are metals such as nickel and iron. Each of these metals have the special property of being able to be magnetized uniformly. When we ask how a magnet works we are simply asking how the object we call a magnet exerts it’s magnetic field. The answer is actually quite interesting.

In every material there are several small magnetic fields called domains. Most of the times these domains are independent of each other and face different directions. However, a strong magnetic field can arrange the domains of any ferromagnetic metal so that they align to make a larger and stronger magnetic field. This is how most magnets are made.

The major difference among magnets is whether they are permanent or temporary. Temporary magnets lose their larger magnetic field over time as the domains return to their original positions. The most common way that magnets are produced is by heating them to their Curie temperature or beyond. The Curie temperature is the temperature at which a ferromagnetic metals gains magnetic properties. Heating a ferromagnetic material to its given temperature will make it magnetic for a while. While heating it beyond this point can make the magnetism permanent. Ferromagnetic materials can also be categorized into soft and hard metals. Soft metals loses their magnetic field over time after being magnetized while hard metals are likely candidates for becoming permanent magnets.

Not all magnets are manmade. Some magnets occur naturally in nature such as lodestone. This mineral was used in ancient times to make the first compasses. However, magnets have other uses. With the discovery of the relation between magnetism and electricity, magnets are now a major part of every electric motor and turbine in existence. Magnets have also been used in storing computer data. There is now a type of drive called a solid state drive that allows data to still be saved more efficiently on computers.

We have written many articles about magnets for Universe Today. Here’s an article about the Earth’s magnetic field, and here’s an article about the bar magnet.

If you’d like more info on Magnets, check out NASA’s Discussion on Magnets, and here’s a link to an article about Magnetic Fields.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
NASA
Wikipedia