Ferrite resistivity

[George Herold]

About what temperature do they work down to?

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.

 

[Tim Williams]

Amidon is a Fair-Rite distributor, so that similarity isn't accidental.

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

 

[Spehro Pefhany]

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.

Thanks, so surely useless at 4K


Best regards,
Spehro Pefhany

 

[Mr Stonebeach]

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).

Tim

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

 

[George Herold]

Thank you,  There's nothing wrong with old knowledge.

George H.- Hide quoted text -

- Show quoted text -

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.

 

[George Herold]

Thanks, so surely useless at 4K

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.

 

[George Herold]

  Thanks Tim, Phil, this is interesting. So the materials listhttps://www.amidoncorp.com/pages/specificationswhich 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

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.

 

[Adrian Jansen]

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.

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.

 

[Jeroen Belleman]

Interesting. Maybe "Ferrites" by Smit& Wijn (1959)? There's the full
text on archive.org, http://tinyurl.com/9pw24tw . Looks like a good
read. A quick glance shows no plots extending below 77K.

(Merci, Monsieur Google.)

Cheers

Phil Hobbs

There are a few plots going down to about 77K in Snelling's "Soft
Ferrites", but nothing lower that I could find.

Jeroen Belleman

 

[Adrian Jansen]

Interesting. Maybe "Ferrites" by Smit & Wijn (1959)? There's the full
text on archive.org, http://tinyurl.com/9pw24tw . Looks like a good
read. A quick glance shows no plots extending below 77K.

(Merci, Monsieur Google.)

Cheers

Phil Hobbs

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

Amazing that its available on-line.