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New Superconductor Found "Immune To Magnetism"

Posted by kdawson on from the north-south-it's-all-the-same-to-me dept.

Lisandro sends in news that testing of the new class of superconductors we discussed a while back (compounds of iron, lanthanum, and rare earths) has turned up a major surprise: magnetism doesn't shut off the superconducting state. Magnetic fields represent one of three factors that limit expanded applications for superconductors (the others are current density and temperature dependence.) The research will appear in Nature; here's a preprint (PDF).

24 of 201 comments (clear)

  1. Another limit? by abbamouse · · Score: 2, Informative

    I seem to recall that one limit was simply the ceramic nature of most superconductors. If it isn't ductile, you can't use it for wires -- which are kind of important for most superconducting applications. Am I wrong about this?

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    1. Re:Another limit? by fyngyrz · · Score: 4, Informative

      You've reached the wrong conclusion; if it isn't ductile, you can't use it for wires that bend; however, you can certainly use it for wires that follow nonlinear paths.

      --
      I've fallen off your lawn, and I can't get up.
    2. Re:Another limit? by mshannon78660 · · Score: 4, Informative

      That's a limitation, rather than a limit. Not being ductile makes it less convenient to use. With magnetism, current density and temperature, the superconductivity disappears as each value reaches a critical point (the limit).

    3. Re:Another limit? by Chris+Burke · · Score: 2, Informative

      Right. You won't be running power lines made of ceramics (because of the temperature requirement too) but it's no problem for a fixed installation like a supercomputer.

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    4. Re:Another limit? by JoeBuck · · Score: 4, Informative
      The original superconductors were metals for the most part, but only work at liquid helium temperatures. Then a new class of high-temperature superconductors were discovered, some of which work at liquid nitrogen temperatures; this second class is often called "cuprate superconductors" and they could be described as ceramic. The lack of ductility isn't as bad a problem as the low tolerance for magnetic field that still superconducts at 45 tesla (basically the strongest magnetic field the experimenters could produce).

      Since flowing current creates a magetic field, you can't use cuprate superconductors to carry large currents. Evidently a completely new class of materials has been discovered.

    5. Re:Another limit? by who+knows+my+name · · Score: 5, Informative

      optical fibres are amorphous, and definitely not ductile. However they are used for miles of cable. You can bend them a few degrees, which is all you really need. I suppose a superconducting ceramic would be worse, but you could still get a significant bend over a kilometre. I think the main barrier is still temperature, I think I read the best we have so far is just above the boiling point of Nitrogen, ~80K

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    6. Re:Another limit? by compro01 · · Score: 4, Informative

      Actually, they're currently working on using a LN-cooled superconductor link in NYC to link some substations in Manhattan. It would replace an oil-cooled copper link. They're expecting to have it running in 2010.

      link

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    7. Re:Another limit? by negRo_slim · · Score: 4, Informative

      Aye.. the highest temperature superconductor is mercury thallium barium calcium copper oxide (Hg12Tl3Ba30Ca30Cu45O125) at 138 K.

      --
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    8. Re:Another limit? by caffeinated_bunsen · · Score: 5, Informative

      As I understand it, they embed the superconducting material in a soft, non-superconducting metal like silver. There's a proximity effect at boundaries between superconductors and normal metals which allows the superconducting state to extent a short distance into the normal metal -- think of it as the Cooper pairs leaving the superconductor and taking a bit of time to notice that they're in a normal metal and split into single electrons. If the layers of normal metal between the superconducting grains are thin enough, then the supercurrent can run from one grain to the next, through the normal metal, without experiencing resistance.

      The ductility of the metal allows some flexibility and tolerance for thermal expansion, as well as providing a low resistance at high temperatures. That's useful because the ceramic materials have rather high resistance when they're not superconducting, which means that if a small segment of wire warmed up above the transition temperature, its suddenly high resistance and the large current flowing through it would cause it to heat up extremely rapidly. The silver provides a secondary current path, so the wire's likely to heat up slowly enough to turn the power off before the wire melts.

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    9. Re:Another limit? by flux+pinner · · Score: 5, Informative

      There are a variety of techniques (depending on the application) that manufacturers use to overcome the inherent brittle nature of most superconductors.

      For magnet windings, the preferred technique is to fabricate the wire from ductile precursors, draw to final size, wind the coil, and then perform a heat treatment to react the precursors and form the brittle, superconducting phase. This, for example, will be the technique used when brittle Nb3Sn is used in the magnets for the ITER project.

      A related solution is to grind the brittle superconductor into powder, insert it into a tube, and use the natural rolling and sliding action of the particles to draw the material into a fine wire that can be subsequently wound into a magnet, with a heat treatment employed to sinter the powder particles back together to form a continuous superconducting path. This is a common technique for MgB2 superconductors.

      For non-magnet applications (like power transmission), the preferred technique is to make a tape (e.g. YBCO) that has only a very thin layer of brittle superconductor. Just like a glass fiber, this very thin layer has a very small bending moment in one direction, and so can be spooled (and unspooled) in this direction, allowing you to manage long lengths.

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    10. Re:Another limit? by Bat+Country · · Score: 2, Informative

      From the two links you pasted, apparently most of Brazil, much of Eastern Europe, central Mexico, and the northern center of North America.

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    11. Re:Another limit? by fyngyrz · · Score: 2, Informative

      Northeastern Montana, for one. Right where I live.

      But for more details, go here.

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    12. Re:Another limit? by Anonymous Coward · · Score: 2, Informative

      I worked in a group at Argonne Natl. Lab that formed wire out of the cuprate materials. We had magnetic coils, high current transmission bars, etc. All were ceramic and brittle but usable. The were formed by slowly burning the binder out of green forms that would later sinter into a solid product.

      The issues that restricted further development was critical current density, which would limit the amount of current and the strength of the magnetic field.

    13. Re:Another limit? by TheLink · · Score: 2, Informative

      Some parts of India. Some parts of Australia. And it seems quite a lot of places on the map you linked to.

      There's always a chance that seismic activity could break stuff. But that hasn't stopped people from _rebuilding_ stuff in earthquake zones.

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  2. Summary is flat-out wrong. by caffeinated_bunsen · · Score: 5, Informative

    Read that preprint, or at least look at the pictures -- specifically Fig. 6. It's a measurement of the upper critical field (i.e. the magnetic field that destroys the superconducting state) versus temperature. The 90% line (where the resistivity is 90% of its normal-state value) does indeed go off the graph at low temperatures; it extrapolates to about 60 T for 5 K.

    There's a big difference between "This material has a very high critical field" (which is what the article said) and "This material has no critical field" (which is what the summary said).

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    1. Re:Summary is flat-out wrong. by mako1138 · · Score: 4, Informative

      http://en.wikipedia.org/wiki/National_High_Magnetic_Field_Laboratory

      There's a 60T pulsed magnet at LANL. "Power comes from a pulsed power infrastructure which includes a 1.43 gigawatt motor generator and five 64 megawatt power supplies. The 1200-ton motor generator sits on a 4800-short ton (4350 t) inertia block which rests on 60 springs to minimize earth tremors."

      And they're building a 100T edition.

  3. reality check by Anonymous Coward · · Score: 5, Informative

    I am a condensed-matter physicist but not a superconductor specialist.

    The article does not say that the material is immune to magnetism.

    The data relevant to this discussion is presented in Fig. 6 in the paper, which is a plot of the upper critical field (the maximum field the material can support and still be superconducting) versus temperature. Look at the traces marked with square markers.

    Notice that these curves do not diverge to infinity as the summary would have you believe.

    Granted, values in the 50's of Tesla seem pretty big, considering that the ambient magnetic field on Earth is about 0.5 Tesla. But note that other superconductors have critical fields in this same range. The famous high-Tc superconductor YBCO has a critical field of 135 Tesla (ref: http://www.springerlink.com/content/j0128jt30843362u/)

    Compared to elemental superconductors, whose critical fields are around 1 Tesla or less, this material does indeed support a lot more magnetic field. But it certainly isn't "immune to magnetism"

    1. Re:reality check by necama · · Score: 5, Informative

      Granted, values in the 50's of Tesla seem pretty big, considering that the ambient magnetic field on Earth is about 0.5 Tesla. I'm just quibbling on units -- the Earth's magnetic field is 0.5 gauss, or, 50 microTesla. Other than that, I agree with your comment 100%.

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      Just another condensed matter physicist.
  4. Bad headline! Bad! by Anonymous Coward · · Score: 1, Informative

    Immune to magnetism? Not even immune to fields we can reach!

    As mentioned by caffeinated_bunsen above, the upper critical field at 0 K extrapolates to "only" about 60 T; higher values are common in the (now 20 years old) cuprate superconductors. (Actually, the upper critical field is really a poorly defined concept in the cuprates, because it's more of a slow crossover, with remnant superconductivity persisting up to much higher fields than we can produce.)

    Also, 60 T is not an inaccessible field by far; several facilities in the world have several pulsed magnets capable of this, with some up to 100 T. More destructive multi-stage, one-shot methods (involving explosives to implode current-carrying coils) can reach 1000 T! These fields require giant capacitor banks, but it's quite possible to produce them in a lab (and not just on a neutron star).

  5. Re:60 T is pretty strong by Anonymous Coward · · Score: 1, Informative

    10,000 T is instantly lethal to organic life

    wikipedia says 0.1MT (10^5 T). that's 100000 T
  6. Re:60 T is pretty strong by xorbe · · Score: 2, Informative

    10^5 is 100,000 T (instantly lethal to organic life)

  7. Re:Or other liquid... by Fear+the+Clam · · Score: 2, Informative

    I read an article in the last year that talked about using liquid hydrogen to cool super conducting transmission lines and also being used as an infrastructure to distribute hydrogen for use in cars, fuel cells, etc...

    Me too. It was this article in Scientific American.

  8. Re:Internal Resistance by jhantin · · Score: 3, Informative

    Is there something that happens at 0F? Ice and salt at 1 atm will stabilize at 0 degrees Fahrenheit; the zero point was originally defined in terms of ice and ammonium chloride.
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  9. Re:Internal Resistance by TheLink · · Score: 3, Informative

    "And I can never remember how to do it"

    Use Google.

    e.g. http://www.google.com/search?hl=en&q=0F+in+C

    It does other unit conversions kph to mph, US gallon to UK gallons, currency conversion.

    And also stuff like how long it takes to transfer 700MB over a 512Kbps link:

    http://www.google.com/search?hl=en&q=700+MB%2F+512kbps
    http://www.google.com/search?hl=en&q=700+MB%2F+512Kbps+in+seconds

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