“The difference is that in the big magnets the tiny magnets are organized, i.e., they’re all lined up with their north poles in one direction and their south poles in the opposite direction. In an ordinary ferromagnetic material, the tiny magnets are scattered every which way, and their magnetic fields cancel each other out, so no magnetism overall.”
[…]
“Well, in chromium and manganese, each atom with “up” magnetism is paired with an atom of “down” magnetism, cancelling out the magnetism of the substance as a whole. In iron, however, all the atomic magnets point in the same direction, so it does (or can) have magnetism overall.”
Apples and oranges, dude. In ferromagnetic materials, ATOMS do not pair up, so they’re free to point in any direction. If they’re pointing in random directions, the chunk of iron they’re in won’t be magnetized. If they are all pointed in the same direction, the iron IS magnetized. If exposed to a weak magnetic field, the iron atoms temporarily align with each other, and the resulting forces make the iron “stick” to the magnet.
No matter what you do, you can’t unpair the cobalt or magnesium atoms, so there’s no NET alignment possible, not even enough to stick to a magnet.
Aluminum is not entirely oblivious to magnetism. My brother works on MRI machines, and he showed me an interesting trick. He stood a sheet of aluminum on edge in the MRI’s intense field, and he let go of it. It fell over, but very, very slowly. Across the room, it would have fallen right away.
The magnetic field of the MRI created an electrical current in the Al which created a magnetic field around the Al which is what slowed the fall. But this requires a changing magnetic field. The falling over is what changes the field in the Al. A static field won’t create the current, etc. This will also work with copper and other non-magnetic materials. (Even conducting non-metals.)
AskNott, see if you can get your brother to cut some slits in the aluminum sheet (so it looks like a giant comb) before trying this. You may be surprised at the results.
The response of aluminum to a magnet relies on eddy currents flowing around the edge of the aluminum. With slits in the sheet, the currents would have to flow much further or enclose much less area, so they’d be less effective, and the aluminum would fall as normal. On the other hand, if you just cut out the middle of the sheet, leaving a big loop, the eddy currents could get around just fine.
Just wanted to say this article about why magnets are not attracted to aluminum is just fascinating, a great article. I have just joined your site, having found the article in reply to a google search on this topic, and have registered this evening. If this is the sort of article your posters (posting folk) post, I will come here often. Thank you very much. HelenML
Welcome, Helen! It’s usually considered bad form to resurrect a ‘dead’ thread (and this one is quite deceased, being six years+change old) but don’t worry: It isn’t a big deal, and you’re new.
There’s a reference I found once (long gone?) in a science article to droping a sheet of copper in a strong magnetic field. It melts on the way through, the eddy current ehat melting the metal.
Similar to why you don’t put aluminum in a microwave - the induced eddy currents cause interesting effects. I was buying something at a deli once, and the girl there had put a paper-backed aluminum foil puch ing one. She then turned to take the cash, oblivious to the package flashing away behind her in the microwave.
But that’s an effect of induced current, for conductors. Metals like aluminum and copper can be conductors and yet not magnetic.
