Some of the best magnets are alloys mixtures of these elements with one another and with other elements. Ferrites compounds made of iron, oxygen, and other elements also make superb magnets. Materials like iron turn into good temporary magnets when you put a magnet near them, but tend to lose some or all of their magnetism when you take the magnet away again. We say these materials are magnetically soft. By contrast, alloys of iron and the rare-Earth metals retain most of their magnetism even when you remove them from a magnetic field, so they make good permanent magnets.
We call those materials magnetically hard. Is it true to say that all materials are either magnetic or nonmagnetic? People used to think that but scientists now know that the materials we consider to be nonmagnetic are also affected by magnetism, though extremely weakly. The extent to which a material can be magnetized is called its susceptibility. Scientists have a number of different words to describe how materials behave when you put them near a magnet which is another way of saying when you put them inside a magnetic field.
Broadly speaking, we can divide all materials into two kinds called paramagnetic and diamagnetic, while some of the paramagnetic materials are also ferromagnetic. It's important to be clear what these confusing words actually mean Make a sample of a magnetic material and hang it from a thread so it dangles in a magnetic field, and it will magnetize and line itself up so its magnetism is parallel to the field.
As people have known for thousands of years, this is how exactly a compass needle behaves in Earth's magnetic field. Materials that behave this way are called paramagnetic. Metals such as aluminum and most nonmetals which you might think aren't magnetic at all are actually paramagnetic, but so weakly that we don't notice. Paramagnetism depends on temperature: the hotter a material is, the less it's likely to be affected by nearby magnets. Photo: We think of aluminum used in drinks cans like these as nonmagnetic.
That helps us separate for recycling our aluminum cans which don't stick to magnets from our steel ones which do. In fact, both materials are magnetic. The difference is that aluminum is very weakly paramagnetic, while steel is strongly ferromagnetic. Photo courtesy of US Air Force. Some paramagnetic materials, notably iron and the rare-Earth metals, become strongly magnetized in a field and usually stay magnetized even when the field is removed.
We say materials like this are ferromagnetic, which really just means they're "magnetic like iron. You can also destroy or weaken ferromagnetism if you hit a magnet repeatedly. We can think of paramagnetic and ferromagnetic materials as being "fans" of magnetism: in a sense, they "like" magnetism and respond positively to it by allowing themselves to be magnetized. Not all materials respond so enthusiastically. If you hang some materials in magnetic fields, they get quite worked up inside and resist: they turn themselves into temporary magnets to resist magnetization and weakly repel magnetic fields outside themselves.
We call these materials diamagnetic. Water and lots of organic carbon-based substances, such as benzene, behave this way. In the early 20th century, before scientists properly understood the structure of atoms and how they work, they came up with an easy-to-understand idea called the domain theory to explain magnetism. A few years later, when they understood atoms better, they found the domain theory still worked but could itself be explained, at a deeper level, by the theory of atoms. All the different aspects of magnetism we observe can be explained, ultimately, by talking about either domains, electrons in atoms, or both.
Let's look at the two theories in turn. Imagine a factory somewhere that makes little bar magnets and ships them out to schools for their science lessons. Picture a guy called Dave who has to drive their truck, transporting lots of cardboard boxes, each one with a magnet inside it, to a different school. Dave doesn't have time to worry which way the boxes are stacked, so he piles them inside his truck any old how. The magnet inside one box could be pointing north while the one next to it is pointing south, east, or west.
Overall, the magnets are all jumbled up so, even though magnetic fields leak out of each box, they all cancel one another out. The same factory employs another truck driver called Bill who couldn't be more different. He likes everything tidy, so he loads his truck a different way, stacking all the boxes neatly so they line up exactly the same way. Can you see what will happen?
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The magnetic field from one box will align with the field from all the other boxes The cab will be like a giant north pole and the back of the truck a huge south pole! What happens inside these two trucks is what happens on a tiny scale inside magnetic materials. According to the domain theory, something like an iron bar contains lots of tiny pockets called domains.
Each domain is a bit like a box with a magnet inside. See where we're heading? The iron bar is just like the truck. Normally, all its onboard "boxes" are arranged randomly and there's no overall magnetism: the iron is not magnetized. But arrange all the boxes in order, make them all face the same way, and you get an overall magnetic field: hey presto, the bar is magnetized. When you bring a magnet up to an unmagnetized iron bar and stroke it systematically and repeatedly up and down, what you're doing is rearranging all the magnetic "boxes" domains inside so they point the same way.
Domain theory explains what happens inside materials when they are magnetized. In an unmagnetized material left , the domains are randomly arranged so there is no overall magnetic field. When you magnetize a material right , by stroking a bar magnet over it repeatedly in the same direction, the domains rearrange so their magnetic fields align, producing a combined magnetic field in the same direction. This theory explains how magnetism can arise, but can it explain some of the other things we know about magnets? If you chop a magnet in half, we know you get two magnets, each with a north and south pole.
That makes sense according to the domain theory. If you cut a magnet in half, you get a smaller magnet that's still packed with domains, and these can be arranged north-south just like in the original magnet. What about the way magnetism disappears when you hit a magnet or heat it? That can be explained too. Imagine the van full of orderly boxes again. Drive it erratically, at really high speed, and it's a bit like shaking or hammering it. All the boxes will jumble up so they face different ways and the overall magnetism will disappear. Heating a magnet agitates it internally and jumbles up the boxes in much the same way.
The domain theory is easy enough to understand, but it's not a complete explanation. We know that iron bars aren't full of boxes packed with little magnets—and, if you think about, trying to explain a magnet by saying it's full of smaller magnets isn't really an explanation at all, because it immediately prompts the question: what are the smaller magnets made of?
Fortunately, there's another theory we can turn to. Back in the 19th century, scientists discovered they could use electricity to make magnetism and magnetism to make electricity.
James Clerk Maxwell said that the two phenomena were really different aspects of the same thing—electromagnetism—like two sides of the same piece of paper. Electromagnetism was a brilliant idea, but it was more of a description than an explanation: it showed how things were rather than explaining why they were that way. It wasn't until the 20th century, when later scientists came to understand the world inside atoms , that the explanation for electromagnetism finally appeared. We know everything is made of atoms and that atoms are made up of a central lump of matter called the nucleus.
Minute particles called electrons move around the nucleus in orbit, a bit like satellites in the sky above us, but they also spin on their axis at the same time just like spinning tops. We know electrons carry electric currents flows of electricity when they move through materials such as metals. Electrons are, in a sense, tiny particles of electricity. Now back in the 19th century, scientists knew that moving electricity made magnetism. In the 20th century, it became clear that magnetism was caused by electrons moving inside atoms and creating magnetic fields all around them.
Domains are actually groups of atoms in which spinning electrons produce an overall magnetic field pointing one way or another. Artwork: Magnetism is caused by electrons orbiting and spinning inside atoms. Note that this picture is not drawn to scale: most of an atom is empty space and the electrons are actually much further from the nucleus than I've drawn here. Like the domain theory, atomic theory can explain many of the things we know about magnets, including paramagnetism the way magnetic materials line up with magnetic fields. Most of the electrons in an atom exist in pairs that spin in opposite directions, so the magnetic effect of one electron in a pair cancels out the effect of its partner.
But if an atom has some unpaired electrons iron atoms have four , these produce net magnetic fields that line up with one another and turn the whole atom into a mini magnet. When you put a paramagnetic material such as iron in a magnetic field, the electrons change their motion to produce a magnetic field that lines up with the field outside. What about diamagnetism? In diamagnetic materials, there are no unpaired electrons, so this doesn't happen. The atoms have little or no overall magnetism and are less affected by outside magnetic fields. However, the electrons orbiting inside them are electrically charged particles and, when they move in a magnetic field, they behave like any other electrically charged particles in a magnetic field and experience a force.
SIX things to know about magnets Almost everyone knows these six basic facts about how magnets behave: A magnet has two ends called poles , one of which is called a north pole or north-seeking pole, while the other is called a south pole or south-seeking pole. The north pole of one magnet attracts the south pole of a second magnet, while the north pole of one magnet repels the other magnet's north pole. So we have the common saying: like poles repel, unlike poles attract.
A magnet creates an invisible area of magnetism all around it called a magnetic field. The north pole of a magnet points roughly toward Earth's north pole and vice-versa. That's because Earth itself contains magnetic materials and behaves like a gigantic magnet. If you cut a bar magnet in half, it's a bit like cutting an earthworm in half! You get two brand new, smaller magnets, each with its own north and south pole. This is, of course, a joke. You don't get two worms if you cut a worm in half. But you do get two magnets. If you run a magnet a few times over an unmagnetized piece of a magnetic material such as an iron nail , you can convert it into a magnet as well.
This is called magnetization. What is a magnetic field? Earth the Magnet Why do magnets point north or south? How can we measure magnetism? What is an electromagnet? Magnetism and electricity: the theory of electromagnetism Electromagnets show that you can make magnetism using electricity. What use are magnets? Which materials are magnetic?
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How different materials react to magnetism Scientists have a number of different words to describe how materials behave when you put them near a magnet which is another way of saying when you put them inside a magnetic field. Paramagnetic Make a sample of a magnetic material and hang it from a thread so it dangles in a magnetic field, and it will magnetize and line itself up so its magnetism is parallel to the field. Ferromagnetic Some paramagnetic materials, notably iron and the rare-Earth metals, become strongly magnetized in a field and usually stay magnetized even when the field is removed.
Diamagnetic We can think of paramagnetic and ferromagnetic materials as being "fans" of magnetism: in a sense, they "like" magnetism and respond positively to it by allowing themselves to be magnetized. What causes magnetism? Explaining magnetism with the domain theory Imagine a factory somewhere that makes little bar magnets and ships them out to schools for their science lessons. Explaining magnetism with the atomic theory The domain theory is easy enough to understand, but it's not a complete explanation.
A brief history of magnetism Ancient world: Magnetism is known to the ancient Greeks, Romans, and Chinese. The Chinese use geomantic compasses ones with wooden inscriptions arranged in rings around a central magnetic needle in Feng Shui. Magnets gain their name from Manisa in Turkey, a place once named Magnesia, where magnetic lodestone was found in the ground. Frenchman Petrus Perigrinus also called Peter of Maricourt makes the first proper studies of magnetism. Coulomb also makes important studies of electricity, but fails to connect electricity and magnetism as parts of the same underlying phenomenon.
James Clerk Maxwell — publishes a relatively complete explanation of electricity and magnetism the theory of electromagnetism and suggests electromagnetic energy travels in waves paving the way for the invention of radio. Pierre Curie — demonstrates that materials lose their magnetism above a certain temperature now known as the Curie temperature.
Wilhelm Weber — develops practical methods for detecting and measuring the strength of a magnetic field. French physicist Pierre Weiss — proposes there are particles called magnetrons, equivalent to electrons, that cause the magnetic properties of materials and outlines the theory of magnetic domains. Two American scientists, Samuel Abraham Goudsmit —78 and George Eugene Uhlenbeck —88 , show how magnetic properties of materials result from the spinning motion of electrons inside them. Sponsored links.
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To do so, weather forecasters would need to combine conventional forecasts with accurate predictions of the Sun's spiral-shaped magnetic field known as the heliospheric magnetic field HMF , which is spewed out as the Sun rotates and is dragged through the solar system by the solar wind. Lead author of the research Dr Matt Owens said: "We've discovered that the Sun's powerful magnetic field is having a big influence on UK lightning rates. The results build on a previous study by University of Reading researchers, also published in Environmental Research Letters , which found an unexpected link between energetic particles from the Sun and lightning rates on Earth.
Professor Giles Harrison, head of Reading's Department of Meteorology and co-author of both studies, said: "This latest finding is an important step forward in our knowledge of how the weather on Earth is influenced by what goes on in space. The University of Reading's continuing success in this area shows that new insights follow from atmospheric and space scientists working together. Dr Owens continued: "Scientists have been reliably predicting the solar magnetic field polarity since the s by watching the surface of the Sun.
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We just never knew it had any implications on the weather on Earth. We now plan to combine regular weather forecasts, which predict when and where thunderclouds will form, with solar magnetic field predictions. This means a reliable lightning forecast could now be a genuine possibility. The scientific paper is freely available and can be downloaded from Environmental Research Letters.