What Can Be Magnetic?

Discussion in 'Chemistry' started by Orleander, Sep 24, 2009.

  1. Orleander OH JOY!!!! Valued Senior Member

    I know solids can be magnetic, but can liquids and gases? Can you make mercury magnetic?
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  3. James R Just this guy, you know? Staff Member

    Actually, virtually every substance is magnetic to some extent. There are actually three different types of magnetism, called paramagnetism, diamagmetism and ferromagnetism. The strongest kind is ferromagnetism. The "ferro-" refers to iron, and this is the type of magnetism that iron magnets have. The other two types of magnetism tend to be much weaker. Ferromagnetism only tends to be found in a few elements, with iron being the most common one.

    Magnetism of one kind or another is intrinsic to most atoms. Get a lot of atoms together in a solid lump, like a lump of iron, and the effect is multiplied. But iron vapour is still magnetic. So is oxygen gas, but to a much smaller degree.
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  5. CheskiChips Banned Banned

    Is anything truly neutral?
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  7. draqon Banned Banned

    what makes iron so strong of a magnet?
  8. James R Just this guy, you know? Staff Member

    Ferromagnetism, such as in iron, is due to a particular quantum mechanical effect called exchange coupling. It causes all the little magnets of individual atoms to line up with each other, which vastly increases the net field strength of the magnet.
  9. kevinalm Registered Senior Member

    A long time ago I saw a demonstration of magnetism in oxygen. After the usual shatter of the rubber ball dipped in LOX and the mandatory cigar 'blowtorch' the professor poured the remaining liquid oxygen into the gap of a large horseshoe magnet. I can still see in my mind's eye the glob of LOX hanging in the gap boiling furiously. Way cool.

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    Last edited: Sep 24, 2009
  10. Orleander OH JOY!!!! Valued Senior Member

    what is iron vapour? And how is oxygen magnetic?
    If I put an magnet in a room full of oxygen, its kind of a given that oxygen will be all around the magnet. :shrug:
  11. Nasor Valued Senior Member

    And anti-ferromagnetism, and ferrimagnetism.
  12. Nasor Valued Senior Member

    If you keep heating iron it will first melt and then boil, turning into a gas of iron vapor (much like water boils to produce water vapor).
    Yes, but a magnet will actually pull the oxygen around much like it would iron filings. The oxygen will tend to stick around the magnet, since it is attracted to it. But you need a very strong magnet to have any significant effect. At room temperature most normal magnets will have very little effect on oxygen gas. It's far easier to see/detect if you do it with liquid oxygen, since then you can actually see it.
  13. noodler Banned Banned

    We know that magnetic fields exist around metal conductors - make a current flow around a series of loops and the magnetic field lines all line up along the axis. The electrons all move in the same direction and the magnetic field is proportional to the current.

    Current is flow of charge or translation; magnetic "charge' is flow of spin density, when charge 'orbits' a center. You have charge density or capacitance, and spin density or magnetic "capacitance" (flux density), both these can form density waves in gases. This is because the gas molecules are free to spin in the same direction under an applied field.

    In metals the electrons are free like a gas (of charged particles), so that ferromagnetism is analogous to fixed waves of spin density, or a quantum effect, as if a strong external field keeps the electrons in place, aligned along the same direction of spin - the magnetic field lines. The strong field is entirely internally generated and is connected to Pauli's exclusion principle.

    Current in metals is charge density fluctuation, when you force this to oscillate you have an AC circuit. Because charge density fluctuates, so does spin density; it's only in very cold gases under high strength fields, that the spin waves can set up because charge density is smoothed out.

    Magnetic fields are electric fields in motion, which is not linear motion.
    Just to clinch it, solids liquids or gases are the same thing to a mass spectrometer, and these use a fixed magnetic field to separate ions with different masses, as they accelerate under gravity.
    Last edited: Sep 24, 2009
  14. Fraggle Rocker Staff Member

    The molten iron in the earth's core has a strong magnetic field, right guys? That's why the north magnetic pole wanders around slowly.
    Every type of matter can occur in three states: solid, liquid and gas (or "vapor"). A solid has a distinct boundary between itself and the rest of the universe, a constant size and a fixed shape. A liquid has a distinct boundary and a constant size but a variable shape. A gas does not have a distinct boundary and its size is variable.

    Temperature and pressure are the determinants of which state any substance will occupy. Anomalies can occur, for example at normal atmospheric pressure carbon dioxide transforms directly between gaseous and solid ("dry ice") state without ever becoming liquid.

    Some substances in their solid state can have their molecules arranged in different ways, resulting in more compact packing and a higher density. This is usually the result of high pressures that on Earth can only be achieved in a laboratory. This conforms to intuition: if you squeeze something tight enough it will rearrange itself to fit into a smaller space. Water ice can have more than a dozen different crystalline structures besides the hexagonal crystals that make snowflakes so beautiful. But they can only be formed in a lab, except for one that exists in trace quantities in the upper layer of the atmosphere. Except for that one and natural ice, they are all denser than liquid water.
  15. Trippy ALEA IACTA EST Staff Member

    Oxygen is paramagnetic because it's highest occupied molecular orbital consists of 2 degenerate states, and is occupied by two (unpaired) electrons. The presenence of those two unpaired electrons give Oxygen its magnetic properties.
  16. Trippy ALEA IACTA EST Staff Member

    Not that there's anything wrong with this answer, but, to put it another way:
    A solid retains it's shape, and requires no container.
    A liquid fills the bottom of the container it's in.
    A gas fills the container completely.
  17. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Some comments on other post:
    James 2&5: As usual James is fully correct, but I can add a little. The individual atomic magnets of ferromagnetic atom ALWAYS align if the temperature is below a critical temperature (called the Currie Temp, but don’t trust my spelling). This is because that is the lower energy state due to quantum mechanical effects. James, spoke of the “exchange coupling.” This lowers the system energy by the “exchange energy,” which is sort of like a chemical binding energy in that sufficient thermal energy can overcome it. (above the Currie temp.)

    This alignment of atomic magnets, like many others quantum effects, is impossible for humans to understand, except with the math of quantum mechanics: Two macroscopic bar magnets will become counter aligned if close to each other. Superconductivity is also an exchange energy effect.

    The common direction aligned magnetic volume is tiny by human scales and called a magnetic domain. (Usually not the same as a micro crystal of the iron) The reason bulk iron in not magnetic is that there are thousand, if not millions of domains aligned in different random directions producing very little gross magnetic effect. They can be torque by an externally applied magnetic field, to make a bar magnet. Each domain resists changing it orientation and then “flips” but the atoms do not move, only the atomic magnets. This flipping can be observed as follows:

    Wind a “pick up coil” around the iron bar being magnetized by a steadily, but slowly increasing magnetic field. As each domain “flips” there is a brief dB/dT, stronger than the slowly increasing applied field making brief voltage pulses in the audio coil, which via an amplifier and speaker can be heard as a clicking, called "Barkhausen noise", but again don't trust my spelling.

    CheskiChips 3: Yes neutral can be achieved in alloys. The forerunner of GPS, had one of Gold and Platinum, as I recall, as a satellite’s “proof mass,” which was a sphere about one cm in diameter. The proof mass was put into earth orbit and a satellite with tiny thrusters followed it. I.e. kept the proof mass centered in a tiny internal chamber, so the whole satellite followed ONLY a gravitational orbit. Residual air, solar pressure and Earth’s magnetic fields did not effect the proof mass orbit. The US Navy paid for these systems so they could know exactly where their ICBM sub were when they launched, but it is why the Earth gravity field is so well characterized mathematically. (Exactly how many terms in the spherical harmonics is still classified, and I never knew despite making a very significant improvement in satellite production cost. – The proof mass chamber had exactly at the center of mass of the remainder of the satellite or else their mutual gravitational interaction would also influence the orbit of the proof mass. That meant every resistor, wire, piece of insulation foil etc. had to be weighted and carefully located – huge cost, than I reduced for later satellites but telling how is long and complex. Others also helped but I did the analysis and then earth based experiment to confirm it would work. (Probably repaid my entire salary of 30 years for the government)

    Nasor 8: AFAIK the terms anti-ferromagnetism, and ferrimagnetism are not used. James gave the three types.

    PS the reason some of the "rare earths" are so useful in making strong magnets is due to the fact that some of the inner shell electrons are not paired - a net inner shell spin and I think, being inner shell not much effected by chemical effects and less so by thermal effects.

    China produces about 95% of the more important ones and has a policy of reducing their exports (about 8% this year.) Electric car motors critically need rare earth magnets to avoid excessive weight. In a recent article in the people's daily (quoting the US magazine Wired) they noted that: "When you have them by the balls, their hearts and minds will follow."'
    More details on this here: http://www.sciforums.com/showpost.php?p=2377144&postcount=186
    including link to that issue of the People’s Daily.
    Last edited by a moderator: Oct 4, 2009
  18. Nasor Valued Senior Member

    Anti-ferromagnetism is long-range magnetic ordering in which magnetic moments of equal value align anti-parallel to each other, giving you a decrease in magnetic susceptibility below the critical temperature. Ferrimagnetism is long-range magnetic ordering in which magnetic moments of different value align anti-parallel to each other, leaving you with some net moment. There are also even stranger and more complicated types of magnetic behavior that can occur, like super-paramagnetism and magnetic spin-glass behavior.

    At least, that's what they told me in my solid-state physical chemistry class...maybe other fields use different terminology to describe different kinds of magnetic ordering.
    I'm pretty sure there are no metals that will have unpaired inner-shell electrons when they are in solid materials. The phenomenon of unpaired inner-shell electrons only happens in isolated gas-phase atoms, so it doesn't have much applicability to magnetic materials.

    The reason why rare earth elements are so useful for making strong magnets is that the magnetic moments of the atoms depends on the total angular momentum of the electrons, which is the sum of the orbital angular momentum and spin angular momentum. Heavier atoms like the rare-earths can have very high orbital angular momentum contributions to the total angular momentum, giving them much bigger magnetic moments.
    Last edited: Oct 4, 2009
  19. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    First part of that could be true with some definitions of metals, but clearly there is huge application of some of the rare Earths (unpaired inner shell electrons) when lighter weight but stronger than Iron magnets are needed.*

    I tend to think of a metal as dense collection of elements that have lost the local binding of at least one of their outer shell electrons. I.e. some of the electrons are not locally bound to any atom, but free to drift with the entire collection.

    At any temperature there are a few such "free to drift" electrons in non-metals and their number INCREASES with temperature. So these non-metals become better conductors of electricity as the Temperature increases.

    Metals have exactly the opposite temperature characteristic. There are a huge number of "free electrons" in metals and the slight increase in their number with temperature (thermally liberated) is entirely insignificant. In contrasts to non-metals, metals become worse conductors as the temperature increases.

    This is due to the fact that the number of phonons increases with temperature. When an electric field is applied to a metal, the random motion of the free electrons has a directional bias, which is what an electrical current is. When there are more phonons the average net drift speed or electrical current decreases as the electrons collide with phonons more often. I.e. the electron "falling" thru the applied electric field accelerate and gains energy but when it collides with a phonon, it loses much of that energy to the phonon, (Which will scatter with other phonons and soon share the energy it has gained to keep their distribution "thermal" but at a slightly higher temperature. - Repeated billions of times each second is why your toaster works - gets hot.

    You can do a simple informative experiment if you have a "multi-meter" (one that can measure electric resistance (ohms). An incandescent light bulb has printed on it the voltage and Watts, so you can calculate the "hot resistance"
    Measure the "cold resistance" with your ohm meter. You may be surprised to find that because of the greater density of phonons when hot the resistance of that metal filament has nearly doubled with temperature.

    So one operational definition of a metal could be: Any non-gas whose electrical resistance decreases as the temperature is decreased. With this definition of a metal, PERHAPS some material does exist for which the first part of your quoted post is true, but I tend to doubt it still, because the inner shell electronic structures rarely if ever have any significant changes as their atom enters into chemical compounds or is in dense contact with others.

    * Demand for rare-earth metals is forecast to increase by between 10 and 20 percent each year, on the back of growing demand for metals such as neodymium, used to make {permanent magnets in} hybrid electric vehicles and generators for wind turbines.
    From: http://english.peopledaily.com.cn/90001/90780/91344/6754751.html
    Last edited by a moderator: Oct 5, 2009
  20. Nasor Valued Senior Member

    Uhhh...I could be wrong, but like I said, I'm pretty sure there aren't any stable examples of any sort of atom with unpaired inner shell electrons in anything but the gas phase. So far as I know, unpaired electrons in solid materials are always on the outer shell. Although if you know of any specific counter-examples, I would be very interested to read about it.

    The reason why rare-earth elements make good magnets is because their unpaired electrons can have very high orbital angular momentum. Since the magnetic moments of the unpaired electrons in a material depends on the total angular momentum, and orbital angular momentum contributes to total angular momentum, higher orbital angular momentum=higher total angular momentum=higher magnetic moment. So each unpaired electron in a heavy rare-earth elements can have a much higher magnetic moment than an unpaired electron in a lighter element, like iron.

    Edit (forgot to address this):
    There are some examples of metals that in the gas phase will have unpaired electrons in the second-highest energy orbital due to complicated spin exchange interactions, but once any bonds form the orbital energy levels re-arrange and the unpaired electrons all end up in the outer shell.
    Last edited: Oct 5, 2009
  21. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    That is simply nonsense. (See many examples below.) Also you are wrong to think orbital angular momentum has anything to do with being paired or not. The standard designation of the orbital angular moment is: s, p, d, & f with 0, 1, 2, & 3 units of orbital momentum - It does NOT depend on the electrons being paired or not. The total angular monentum does.

    All of the rare earth elements 57 thru71 (All are given by atomic number below to save typing names) have ZERO total outer shell angular momentum. They have 2 paired s electrons so net spin is zero and all s electorns have zero angular momentum. I.e. 0 + 0 = 0.

    The following elements have a 4f unpaired electron: A = 58, 59, 61, 63, 64, 65, 67, 69, & 71.
    The following elements have a 5d unpaired electron: A = 58, & 64.
    The following elements have no unpaired electrons: A = 60, 66, & 70

    But I think you are also somewhat confused as “paired or not” is NOT the most important aspect for their magnetic properties. The pairing refers to the spin pairing. Although you do know that magnetic moment is related to that plus the orbital angular moment, and I hope that f electrons have more orbital angular momentum than d electrons and there can be more of them as there are two more possible projections of the orbital angular momentum. (7 projections for f and only 5 for d electrons)

    When a shell is either completely filled or empty it has no orbital angular momentum and in general a half filled or slight less than half filled shell can have the maximum orbital angular momentum.

    Consider A=60, Nd neodymium. It has NO unpaired electrons, yet makes the most powerful rare earth magnets. That is because it has four f electrons in shell n = 4 well shield from chemical distortion of the n = 4 electrons by 10 electrons in the n = 5 & 6 shells. I am sure that 2 of its 4 n = 4 electrons have zero projection (m = 0, if I remember the standard notation correctly). The other two probably have m = 1 & m = -1 but I am not sure of that. What this means in a classical POV is they are all zipping around in essential the same circular orbit, making a very large magnetic moment that can not be disturbed by being in a solid. When filled, the n = 4 shell will have 14 electrons and zero total angular momentum.

    The electronic structure of 61 Pm promethium is identical with 60, Nd neodymium except for one more n = 4 electron. This would add one unpaired unit of spin in that shell, so perhaps is even better than neodymium if equally easy to obtain. Some of the still higher A rare earths also would seem to be useful, but one must avoid even nearly completing an inner shell.
    Last edited by a moderator: Oct 5, 2009
  22. Nasor Valued Senior Member

    After careful consultation with my old inorganic chemistry textbook, I have concluded that you are correct. Thanks for setting me straight.
  23. draqon Banned Banned

    Plasma is magnetic, it has a self-induced magnetic field.

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