How can a permanent magnet produce magnetic field? What is the principle behind?
The spin of the Electron
gives it a permanent magnetic moment. In most materials the magnetic moments are all opposed and cancel out, but in some an electron in each atom can be made to align predominately in one direction. Iron has two electrons that can be aligned, so it is the "strongest" magnetic material.
Why do some materials have electrons aligned predominately in one direction while some have not?
So are all permanent magnets made of irons? If yes, why can iron be permanent magnets in some case and electromagnet in the other case? (or am I misunderstanding something?)
In the materials that are magnetizable you have to put energy into them to make the electrons opppose each other. The state of least energy is the one with the extra electrons aligned.
Magnetic materials have "domains" where the electrons are lined up together, but in most materials, such as pure Iron, the fields of the domains are directed randomly and cancel. When we apply an external field, such as from a solenoid, the domains will all tend to line up. If we modify the Iron by alloying it, and cool it while it is still magnetized we may "freeze" the domain field orientations and make a permanent magnet.
There are many materials besides Iron which are magnetizable, including some alloys of metals, neither of which is magnetizable by itself. And there are "soft" as well as "hard" magnetic materials.
This is a complex and interesting subject and if you want to understand it better I would suggest some serious reading.
I thought it was because each electron's magnetic field direction was random and over and entire piece of material they cancelled each other out, and in the presence of a magnetic field (ie something that effects charges) they became aligned with the feild.?
That would only give a very weak effect, something like you would see in liquid Oxygen for instance. In true ferromagnets nearly all the domain fields in the material line up in a field of a few kiloGauss.
By the way, Electrons are spinors, so they either line up with or against the ambient field, they can't have just any orientation.
Oh boy, this is a fun subject. This question goes straight to the dark depths of physics. Ok I understand that the electrons have to be lined up in the material of a permanent magnet. I think we learned that in 4th or 5th grade science class. When we took a permanent magnet and ran it across a screwdriver and produced a magnet via aligning the electrons. I remember this question being discussed in the old forum and it created a large difference in opinion. The problem with this question is that in order to truly explain it you need to know what magnetism is? Considering the fact that nobody knows at this point in history, hmmmm leaves it up for speculation. So since we are creating our own theories. With all do respect, let me indulge in my own theory of why the permanent magnet has a magnetic field. I will start by asking questions and giving my answers. My first question is why is an electron magnetic? The reason for that question lies in the fact that if the electron weren’t magnetic in the first place, lining them up would be irrelevant. I am not as great of a physicist as others on this sight so please feel free to tear my theory apart, It won’t hurt my feelings that’s how we learn sometimes. Well, the reason for the electron to have what’s called a magnetic moment is speculated to be created from particle spin. Supposedly this spin creates not the magnetic moment directly but instead causes the particles electric charge. In which the spin is caused by little tiny fairy type people inside the electron, running as fast as they can. This hard work goes unnoticed by the human’s cause they are way to small to see. We are always finding new ways to kill them, like inside super collider. That’s how we discovered their larger brothers the quarks. Which is like a large mass of them actually that held each other’s hands during the meteor impact on their planet. Any way the fairy people of electron village have joined there forces to create a great bond in the universe called magnetism. They are only attracted to the female fairies that are from proton village. They really think there sexy. Although they keep running and trying to hook up, it is very difficult sometimes without the human help. So we help them get together and all is well. So now that I have lost my mind here is my real theory. I believe energy is matter and matter is energy, and that all particles have charge that is created from resonance of that energy/matter. All energy/matter is vibrating or oscillating at specific frequencies. Only certain frequencies are resonant with others and visa versa, repel from other non-resonant energy oscillations. This creates real tiny bonds and reactions. As these bonds and reactions happen more resonant energy coagulates and forms tiny particles that are singing its own tune per say. These tiny particles might bond with other particles to create larger particles or combinations of particles. This causes an evolutionary effect in its formation into more complex forms of bonds until you have what we call an atom. I give up I am tired I will continue the unified field theory at another time good night people of inner space..
I think why magnets have magnetic field is that when electrons in each atom align predominately in one direction, say in clockwise direction, then current flows in anti-clockwise direction. And by right hand grip rule, we can know the direction of the magnetic field produced. (My physics teacher has introduced this concept when he taught about hysteresis loss in a practical transformer)
Do you have any good books to recommend? I want a relatively simple book that doesn't have lots of difficult equations.
In fact I can't imagine the picture of how eletrons in each atom can align in one direction because they don't have a fix orbit, instead we can only find electron clouds with different shapes.
Also I've come across a term that I don't understand. Could someone please explain what is magnetic moment?
So this topic has something related to the unified field theory,right?
I think that everything eventualy falls into the unified field theory. Cause simply all of the forces, including magnetism have a common source that would explain all the properties of each individual force.
K L Kam,
There is an excellent entry on
magnetism in "How It Works,
The Illustrated Encyclopedia Of
Science and Technology" if you can find this in a library somewhere.
You mentioned the cores of trans-
formers. These never become per-
manently magnetized because of
the steel that is used. It is
refered to as "Soft Steel" or
"Mild Steel" because it doesn't
contain the proper amounts of
carbon and other elements, to
allow it to be hardened. Strangely
though, it is highly suseptible
to being magnetized by "induc-
tion". The relatively weak mag-
netic field produced by a current
carrying coil produces a remark-
effect in soft steel, causing all
it's magnetic "domains" to become
"lined up". As soon as the field
from the coil is removed, they
almost completely revert (there
is some residual, weak magnetism)
Hardened steel, as has been
pointed out, does not revert
after the field is removed, and
you have a "permanent" magnet.
The hardening process (heating to
the material's "Curie" temperature
which is in the range of red heat,
and then cooling it as suddenly
as possible (quenching in water,
oil, sometimes a blast of frigid
air) causes a jamming of the
material's microscopic crystaline
structures. It is this crystaline
traffic jam, so to speak, that
wont allow the material to revert
after the magnetizing field is
I've been corrected by Integral, it isn't the spin that is the main contributor but the orbital angular momentum of the electrons which are aligned and give the greatest contribution to the domain field.
This is an interesting topic. One that I have studied for over 20 years.
Unfortunately, you will not find any good books or articles that explain precisely how a magnet works. The last good book I read was written in the 1930's by a scientist from General Electric. Even then, it wasn't a big book.
From what I've seen, either the information discovered about magnets is classified by the government or it doesn't exist. If it is not classified info, then magnets have been virtually ignored by the scientific community for over 70 years!
Most books and articles written about magnets are written by people who really don't understand them. The people are simply repeating what they heard from their instructor and confusing it.
Exactly how the atomic particles are aligned once iron is magnetized, I don't know. I suspect that the orbit of an electron in relation to the size of the nucleus has a lot to do with magnetism.
However, magnets are fascinating in what is going on inside and what they do.
Magnets are essentially a black hole. Unlike a black hole, however, only electrons pass through (not protons and neutrons).
Magnets feed themselves.
Permanent magnets have small areas of influence where they are anti-magnetic as well. Iron based objects are repelled from those areas.
Magnets are unstable in that the output of the magnet is reduced by about 40% at night. Consequently, permanent magnets are not used for commercial electrical production. They have been deemed to be "unstable" as compared to electromagnets. Permanent magnets do not behave the same on a sunny day as they do at night. To the naked eye it looks the same, however.
Magnets are the only "perpetual motion" device we know of that does not physically harm us.
FYI, the core of an electric generator is not "steel". It is what is called soft iron. Steel is iron with carbon introduced to make iron stronger. People who build the core of the generator use plates of soft iron much like the plates in a transformer. There is only one company that I know of in the US that sells soft iron. (CMI Inc.)
All iron based metals are magnetic. If you pass a compass along the side of a steel desk or cabinet, you will see the compass alternate between the north and south pole as you move along the surface of the metal. This is due to the fact that the steel was rolled and was not annealed (reheated) after the rolling process.
It is probably not a good idea to rely too heavily on the scientific community to understand what interests you. It is better to sift through the "scientific" info and determine what is really true.
Case in point. Only in the last 10 years has the scientific community classified a magnet as an electronic device. We have used magnets to produce electricity for almost 200 years and it took that long for the source of most of our electric power to be classified as such.
I guess that is how it is supposed to work?
Also, magnets have far more uses than what we currently imagine. Inter-stellar space travel is possible (at any speed) with the use of permanent magnets. Many, many more uses! But I can't get in to that just yet.
Will someone stop Bill?!
BILL! You belong in the Theory Developement page! I have seen several of his posts, and they're all identical, he just goes around preaching his nonsense gospel of electrons flying in and out of magnets, though I have proved in a different thread that it is impossible. How can he study this for twenty years and not catch on?
Permanent magnets (or ferromagnets) exhibit a magnetic field even in the absense of an applied external field (unlike diamagnetism and paramagnetism). This is called spontaneous magnetization (SM).
As mentioned before, SM is due to alignment of permanent dipoles within the material. The dipoles themselves exist due to contributions from the orbital angular momentum of charged particles (for eg., an electron orbiting a nucleus is equivalent to a current flowing, which generates a dipole moment according to Ampere's Law) and the intrinsic angular momemtum, or spin.
When deriving the properties of dia- and paramagnetic systems, we generally assume that the individual moments are "unaware" of each other. For ferromagnetic materials, SM indicates that this is not the case - each dipole knows the orientation of the other dipoles, through something called the exchange interaction. This is basically a Coulombic interaction between electrons that depends on the orientation of their magnetic moments. Of course, the Coulomb interaction itself does not depend explicitly on spin, but the energy of two electrons does. Ultimately, we calculate the exchange interaction by treating it as a perterbation to the Hamiltonian.
As far as domains go, they are localized regions within the material that possess some net magnetization, where adjacent domains can have different magnetizations (pointing in other directions). The formation of FM domains is primarily due to the desire to have the lowest possible energy. There is a competition going on between various different factors: exchange energy, magnetic energy, and various anisotropic conditions.
For example, if we have a magnetic field B outside the material, there is a net energy per volume inside the material due to B. This energy can be reduced by forming domains which have opposing magnetization, to reduce the effect of B. However, this requires energy to occur, since the transition regions between different magnetizations (called a Bloch wall) need to be formed.
To create a ferromagnet then, we need to align the domains so their magnetizations are aligned, which creates the net field we desire. To do this we can apply a strong external field. As the strength is increased, domains with parallel magnetizations will get bigger, at the expense of those that are antiparallel or perpendicular to the applied field. At this stage, the process is reversible - ie., if we apply a field in the opposite direction we can return the domains to their previous configuration.
If we continue to increase the field strength however, some domains will disappear altogether. At this point we can't reverse back to the start. Magnetic inhomogeneities in the material also come into play at this point (such as pinning of domain walls, etc, etc). Eventually we reach the saturation magnetization of the material, which basically means everything is aligned. If we then remove the external field, the net magnetization will decrease from the saturation value, but will not drop to zero - it will stop at the remnant magnetization, which is ultimately what makes the material a "permanant magnet".
If we bang the material around, or heat it up enough, we can alter the aligned domain structure and reduce it's magnetic field. As well, we can apply a field in the opposite direction. The coercivity of the material is the field required to reduce the magnetization back to zero (this entire process follows a hysteresis loop).
Phew. Magnetism is such a huge topic, it's hard to stop
I think that was really an ex-
ellent post. I haven't run into
an explanation anywhere else that
was so detailed. You sound to me
like you have done serious work
in this area.
P.S. Since Bill informed us that
this kind of info is classified
by the Government I'm sure we all
would like to hear the story of
how you escaped from Area 51.
I'm sorry, that's classified.
Link to a magnetism thread in Physics. There I have linked to a PDF scaned from a E&M text which pretty much echos Futz's post.
What, if anything, would cause a permanent magnet to lose its 'power'. Time or heat? Would it eventually be reduced to zero?
in a previous post it mentioned if the magnet is beaten out of shape it changes the alignment of the electrons or something? Sorry just skimmed over it thus losing its magenetism or 'power' because there are less electrons facing the same way
When a conductor moves around permanent magnet it produces the magnetic field. The magnetic field produced is proportional to the speed of the conductor. The magnetic field decreases as the far from the magnet.
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