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Ferrite resistivity

Discussion in 'Electronic Design' started by George Herold, Sep 14, 2012.

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  1. OK this is a pure speculation. But I'd guess they all change
    somewhere near 120 K.
    As soon as we get some more LN2 in I'll try some tests and post
    results.
    It's apparently a phase change in the Fe2O3 that happens in
    magnetite.
    And all the ferrites have Fe2O3 in them... so....

    George H.
     
  2. Tim Williams

    Tim Williams Guest

    Also Magnetics Inc. and Micrometals, so if you ever want all the data you
    can find, check around. To designate material, Fair-Rite uses two digit
    numbers, Micrometals uses 1-2 digits and color codes, and Magnetics uses
    letters for their ferrites (e.g., W is mu_r = 10k).

    Most of these are also available from other distributors, like Adams
    Magnetic and Elna Magnetics; they have an online searchable inventory, but
    weak or no catalog; they don't have online ordering, but they're
    responsive and nice to deal with.

    I have never seen a powder core that wasn't recognizably Micrometals or
    Magnetics (who also bought Arnold, whose cores are designated with 6-7
    digits). They probably all buy from the same Chinese manufacturer.

    There are more ferrite manufacturers than powdered iron, but most OEMs
    either get something from Fair-Rite, Mag-Inc, Ferroxcube or TDK, or
    something very similar to their products.

    Tim
     
  3. Thanks, so surely useless at 4K


    Best regards,
    Spehro Pefhany
     
  4. Thanks Tim, Phil, this is interesting. So the materials list
    https://www.amidoncorp.com/pages/specifications which looks like its
    Amidons own, is actually compiled from two original suppliers' data,
    whose designations luckily don't overlap (or maybe they have
    coordinated this).

    Regards,
    Mikko
     
  5. Hi Adrian, first I wanted to thank you again. (SED is an amazing
    repository of knowledge.) And second there is a reference in Kittel's
    Solid state physics to a Philips technical review.

    J.J. Went and E.W. Gorter, "Magnetic and electrical properties of
    Ferroxcube materials," Philips Tech. Rev. 13, 181 (1952)

    The local Uni. library seems to have this in deep storage and it's not
    clear that I (as an alumnus) will be able to get access. But if
    anyone has a copy of this old journal I'd really like to know if they
    cover the electrical and magnetic properties at low temperatures (down
    to liquid nitrogen.) If so then I'll put more effort into digging up
    a copy. (After all a few hours in the library can save days in the
    lab!)

    George H.
     
  6. Yeah that's according to Mikko. I think he's looking for one of the
    iron garnets (YIG) that look like they will work at 4K. (Though
    getting them in toroids or some other convenient shape may be hard.)

    George H.
     
  7. Nice!

    I was reading on the Jack Smith's website (clifton labs) that there
    may have been some recent change in the way the 43 material is
    made.

    http://www.cliftonlaboratories.com/estimating_q_of_ferrite_cores.htm

    Which may explain the very high resistivity I measured (or couldn't
    measure :^) for the newer beads.

    Though I didn't report it in my first post, I also found that the
    shorter beads (1/8" length vs 1/4") had a resistivity that was closer
    to what was listed on the spec sheets. This sort of fits with a model
    of a random conduction path through the material. So if I grind down
    thinner samples I may get resistivities that are closer to what I
    expect.

    George H.
     
  8. There was a very good, but very theoretical, book put out by Philips in
    the 1950s ( or maybe even earlier ). Cant give you the title, or even
    the authors, but that paper probably refers to it. Lots of good
    physics, and certainly much more than just the manufacturers
    specifications etc. Extreme low temps were discussed, certainly there
    were plots of permeability over the full temp range, and how they
    related to the compositions, but I dont remember any details.
     
  9. There are a few plots going down to about 77K in Snelling's "Soft
    Ferrites", but nothing lower that I could find.

    Jeroen Belleman
     
  10. Smit & Wijn was the one I remember cutting my teeth on.

    Amazing that its available on-line.
     
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