Sunday, April 22, 2012

How Do Magnets Work?

Update: This video explanation is wonderful: http://youtu.be/1TKSfAkWWN0

You're probably within 10 feet of a half dozen magnets--speakers, fans, hard drives, etc.  They're everywhere, but how do they work?  You've probably gotten supperficial answers before, but if we keep pushing the question a step further and a layer deeper what can we find out?  Well, I wasn't satisfied with the answers I had gotten and set out to find some answers on how magnets really work.



A piece of metal is a magnet because the atoms within the magnet are also tiny dipole magnets and their charges, since they point in the same direction, add their forces together.  (This is the lame non-answer answer that we're usually force fed.  Bump that.  I want to really get it!)



Well, why are atoms dipole magnets?  Why wouldn't their charge be emitted equally in every direction?  Because the electrons have a constant spin orientation.  You see, electrons come in two types--up spin and down spin.  As far as my understanding extends, this really is the kind of spin that we think about, like a globe spinning on its axis, but in completely alien ways--electrons are point particles that have no three dimensional structure.  Weirder yet, they always spin at the same exact speed, even though they can change spin direction.  (Edit: I no longer am confident that magnetism is caused by the spin of electrons.  It may be due to  the spin of protons or an interaction between the two or something else entirely.  I am not a physicist, only a curious biologist.  I welcome you insight, input, and points in the right direction.)



So, how magnetism works is there are electrons spinning in a certain stationary direction all the while buzzing around the nucleus of the atom.  So...why aren't all elements magnetic?  Couple reasons.

First, not all atoms have a balanced ratio of up and down spin electrons.  It turns (o, pun!) out that up spin electrons like down spin electrons (or, they don't repel like those with a similar charge do).  Another seemingly arbitrary rule that physics follows is that up spin electrons move in to open orbitals within electrons subshells up spin first (it has to do with being a lower energy state).  Down spin electrons get pushed to the back of the line for entrance to the electron cloud ride.  It's these imbalances that create a situation  that can cause a directionality to the magnetic field of the atom.



We still have a problem.  A very large, glaring one.  There are plenty of elements that have more up spin than down spin electrons--so called paramagnetic because they are attracted to a magnetic field (their up spins want other down spins).  Ferromagnetism, or the magnetism that we think of, only happens in a pitifully few amount of elements (and depends on what temp you're at)--typically we only really think of iron (hence the 'ferro' prefix), nickel and cobalt.  There are others like gadolinium and dysprosium, et al, but we typically just think of three as magnetic.  Think of it...just three elements out of roughly one hundred and twenty.  Wth?




I must plead your help in finding more answers than this.  I've reached the limit of my knowledge and time constraint to further research why magnetic substances can have their individual magnetic fields align when you place a magnet next to them or run a charge through them while heated.  Could it have to do with a crystalline lattice structure of the atoms?  Could it have to do with the way that the metallic atoms share outer valence electrons?  Do they maintain their spin orientation while moving across atoms?  Could it have to do with an additive effect that the various layers of shells have that work together within a Goldielocks window (Iron, cobalt and nickel all have roughly half filled d orbitals within the first row of d orbitals and the other magnetic metals have roughly half filled f orbitals within the first row of f orbitals...Coincidence?  Not likely.)?  My reading seems to suggest that it is stability of the way the molecules orient in a crystalline structure...And that has to do with the odd and quirky shape of orbitals, which is a whole other blog!  (More like 10 blogs!)

I'm pretty sure that the red is the iron, the neodymium is blue and boron is green.  Together they  make the world's strongest permanent magnet.



We're also still left with the problem of why having 'spin' causes this magnetic field to start on one end and then cycle around to the opposite side of the electron...I have no answers there.  We've reached the frontier of knowledge.

Electrons aren't the only thing with spin.  Nucleuses have spin and MRI machines use the interactions of these spins to make an image.  Photons do, too.  That's what polarization is all about--a particular orientation of photon spin...So much to learn in this field!!


Curie Point demonstration below.  This is the temperature when the atoms become so hot that their bouncing around negates all magnetic domain orientation.





Pix cred:

http://en.wikipedia.org/wiki/Magnet
http://www.tcm.phy.cam.ac.uk/~gjc29/research.html
http://www.magiccalc.net/scienceandmysteries/index.htm
http://chemistry.about.com/od/electronicstructure/ss/aufbau_3.htm
http://www.sciencedirect.com/science/article/pii/S1570002X08002085

http://en.wikipedia.org/wiki/File:Neodymium_Crystal_Structure_Nd2Fe14B.jpg


More:


http://en.wikipedia.org/wiki/Stern_gerlach
http://en.wikipedia.org/wiki/Electron_magnetic_dipole_momenthttp://www.doitpoms.ac.uk/tlplib/ferromagnetic/printall.php
http://www.nature.com/milestones/milespin/index.html
http://en.wikipedia.org/wiki/Antiferromagnetism
http://youtu.be/E97CYWlALEs 

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