What are the smallest (<100 nm) magnetic particles available and where can I purchase them?
537198
See the listing of suppliers given in the source below.  If you want to do magnetic separation, you'll want multi-domain particles, which means using particles *larger* than about 100 nm (depending on the material).
653259
The cheapest ones I've found are at mcminone.com
1174974
Looks like you will only get them online and in bulk.  Here is a site which offers a sample.  It might be a way to get just one!
76483
cobalt can be used just about anywhere iron could. the primary place would probably use in magnets
1136539
Paramagnetic materials like Aluminum have magnetic properties, but cannot sustain a permanent dipole moment alignment. Hence it qualifies as a candidate for your question.\n\nAlso ferromagnetic materials (common ones are Cobalt, Iron, and Nickel) above their associated curie temperatures behave the same way. No permanent magnetization.
35777
How about purchasing them online at different websites-\n\nhttp://www.maxmax.com/aUVBlueInvisibleInks.htm\nhttp://www.kopes.com/gadgets/invisible-ink-pen-uv-light.htm\nhttp://store.yahoo.com/airline/fisppencaspp2.html\n\nIsn't this the same as magic ink pens too?\nhttp://www.ustoy.com/cgi-bin/ustoy_cgi.sh/WService=ustoy/ustoy.com/novelty/product.htm?stateInfo=?&dept_id=151&pf_id=1043
700634
i heard there are tiny metals ranging in size between\nmicrodots and pieces of wire 1/3rd of an inch.
361293
Do you mean "magnetic"?????
1009498
Dont know much but plz try this\n\nhttp://www.google.co.uk/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=magnetic+particle+testing+the+testing+particles&spell=1
1092387
The closest magnetic source.
457074
Here is a great lab on ferrofluids that I am familiar with. Some info about ferrofluids is in there, too.\n\nhttp://mrsec.wisc.edu/Edetc/nanolab/ffexp/index.html
343621
Try googling "magnetic levitation circuit"\n\nHere is one of the many hits I got.
780568
In this site:\n\nhttp://www.coolmagnetman.com/magacmot.htm\n\nyou will find what you are looking for.  (You may need to jump to another site from there if you want more).
961401
Try a pharmaceutical chemist. They may be able to obtain a small quantity for you.
734023
It sounds like you need a multi-meter which is handy for all your electric household needs. You can measure current with most of these and they can be found in hardware stores like Ace in most cases and possible even at places like Wal-Mart. They are not uncommon items. If you want you might be able to go online and search for a amp meter most likely from a physics teacher website. I'm sure your nearest hardware store will carry coil but if not, Radioshack is an option. Problem with Radioshack that I have had is too much money for too little quantity (this is in general and not specific to the coils) if you have time, you can browse the internet for teacher selling sites but you may have to pay for shipping which might also run up the cost. The magnets really depend on what scale you are talking about. Hobby Stores will definitely carry small craft magnets but if you need really strong magnets your best bet is once again a teacher website. I hope that I have been at least some use to you, and best of luck on your experiment/project.
1139339
The best way is to get it from the manufacturer.  If you don't know who made it, you can look up resistances from a bunch of places on the net if you know the wire gauge, but remember that copper resistance increases as it gets hot.  \n\nMost magnet wire can handle a few hundred volts with no troubles, but if you're doing some high voltage app, better be sure about the voltage rating.
612302
You could build a set of fluid armor as seen in the Matrix movie.\n\nA simple magnetorheological fluid can be home-made out of small magnetic particles mixed with mineral or vegetable oil. Iron filings do not work well; they are too big. Good sources for small magnetic particles are:\n\n* magnetic inspection powder from welding shops\n* particles from burned steel wool (after mortar and pestle)\n* particles scraped from the surface of video tapes\n* particles "mined" from sand with a plastic bag and a magnet (see external links)\n\nThese fluids are not very stable, however. The particles will tend to clump and the fluid properties will be lost quickly. Fluids created for professional purposes use emulsifiers to suspend very small oily (octane or kerosene) magnetic particles in water. The particles are very fine; less than a micrometre in diameter.