Date: Fri Nov 2 19:25:29 2007

Author: Urs Lauterburg

Subject: Re: Labs on Magnetic Materials

Post:
Steve,

This sounds really nice. We use an old magnetic bubble device for
demonstrations and even if it does not quite reflect the shapes of
metallic magnetic domains it still illustrates the concept of having
domains that change their size due to an external magnetic field. The
aesthetics kind of shows the 60ies pop art patterns of The Sergeant
Peppers Lonely Heart Club Band.

Does the statistics of the number of domains in relation to the
external field really comply with a hysteresis cycle? If yes this may
indeed make for a nice lab and image acquisition domain
analysis/counting application.

Great QT-Movie Steve, which I remember having seen on an earlier occasion.

These garnets used to be sold here by Griffin & George Education
http://www.griffineducation.co.uk/
Can one still get them?

Regards from over here

Urs

Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern
Switzerland


>Hi Mary Ann,
>
>This past summer I made a stab at developing an experiment based upon
>that magnetic bubble apparatus. This apparatus, for those of you not
>familiar with it, is a thin film of ferrimagnetic garnet mounted in the
>center of a small wire coil. The garnet is sandwiched between a pair of
>crossed polarizers. It is special in several respects:
>--The magnetic domains point either up, or down.
>--The up and down domains are clearly visible and distinguishable
>in a microscope under 30X magnification (or greater) (because of the
>Faraday effect)
>--It's not a normal ferro or ferri-magnetic type material, in that it's
>insulating, and transparent. Most magnets are metals.
>
>Mounting the apparatus on a microscope stage, I could photograph the
>magnetic domains as a function of applied current, and use the software to
>compute the percentage occuppied by the "up" domains, and get a
>magnetization curve of %magnetized versus applied current. Essentially
>this is the same experiment reported earlier, but far more detail is
>visible, in that the observer sees directly the magnetization.
>
>I think it's potentially a great experiment. I showed it to about a
>half-dozen faculty members, and all agreed that it was very nice.
>Nobody would commit to using it as a lab with their class, though, so
>I dropped the development.
>
>Some things to consider:
>
>-- It'd be nice to have a measurement of the magnetic field produced by
>the coil. I tried using a Vernier magnetic field sensor over the sample,
>but the field was too weak to pick up. It'd be better to mount a tiny
>Hall effect sensor inside the coil at the location of the sample, or
>nearby.
>
>-- It'd be nice to measure to total field (coil + field due to sample),
>too, and get an independent measurement of the magnetization. But as the
>garnet sample is less than 10 microns thick, I'm not certain that the
>field would be large enough to measure.
>
>-- Possibly one could compare the results with those of mean-field theory.
>
>-- Several faculty said that it would be interesting to explore other
>apsects of the domains, for example by calculating the fractal dimension
>and seeing how this depends on magnetization, repeatability, and approach
>to zero current.
>
>Personally, I think this is a fantastic apparatus.
>
>We do have it in use as a demo, where we simply bring a magnet close
>to show the behavior of the demains:
>http://www.pha.jhu.edu/~wonnell/Magnetic_Domains_in_MagneticBubbleApparatus.mov
>
>-- Steve
>
>
>
>
>
>
>
>
>On Wed, 31 Oct 2007 mklasse1@swarthmore.edu wrote:
>
>> Date: Wed, 31 Oct 2007 15:30:06 -0400
>> From: mklasse1@swarthmore.edu
>> Reply-To: tap-l@lists.ncsu.edu
>> To: tap-l@lists.ncsu.edu
>> Subject: [tap-l] Labs on Magnetic Materials
>>
>> Hey, y'all.
>>
>> Does anyone do an intro or intermediate E&M lab on magnetic materials?
>>
>> In particular, do any of you use the Tel-Atomic Magnetic Bubble
>> Apparatus (http://www.telatomic.com/mba.html) for a quantitative
>> experiment? Two articles from the early 1980's, AJP 48(1), 59 (1980)
>> and TPT 20,330 (1982) describe an experiment, but I'm interested in
> > insights to how it works in practice.
>>
>> I also came across another AJP article (66(5), 449 (1998)) that
>> describes mapping the magnetization curve of a toroidal sample of
>> ferromagnetic material. The sample is wrapped with two windings. One
>> winding is connected to a current source, producing a magnetic field,
>> and the other winding is connected to an inductance meter. The
>> inductance is proportional to the magnetic permeability. Does this
>> sound like a familiar experiment to anyone? Thoughts?
>>
>> Are there any other experiments, either quantitative or qualitative
>> you do on this topic that you'd recommend?
>>
>> Thanks!
>> Mary Ann
>>
>> ***********************************************
>> Mary Ann Hickman Klassen
>> Lecturer
>> Dept. of Physics & Astronomy
>> Swarthmore College
>> 500 College Ave.
>> Swarthmore, PA 19081
>> phone: 610-328-8384 fax: 610-328-7895
>> **********************************************
>>


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