MU METAL....is it attracted to a magnet?

[CANGAS]

This is such a rookie question that I am so ashamed to have to ask it.

After researching mu metal the best I know how, I still don't know...is mu metal attracted by a nearby magnet?

Anybody with personal experience that has noticed if it is attracted, or, repelled,  by a magnet?


Many thanks
CANGAS 203

[TinselKoala]

Is mu-metal attracted to a magnet? No, but magnets are attracted to mu-metal...... Lol.




Sorry, couldn't resist. The actual answer to your question is YES, indeed. Mu-metal is a highly permeable nickel-iron-copper-chromium alloy which means it is actually more attracted to a magnet (or vice versa) than other alloys. You can think of it as "sucking in" as much magnetic flux as possible-- thus making the flux unavailable to do other things. Hence it acts as a "shield", not so much by "blocking" flux as by diverting it into itself.

Part of the process of making Mu-metal involves careful heat-treatments, hydrogen annealing which greatly increases the permeability, and this means that machining mu-metal, by milling, grinding, cutting and even bending, can reduce the "mu-ness" of it.

If you take apart a defunct computer hard disk drive, the very strong magnets in the head-positioning unit are attached to chunks of mu-metal that shield the disk itself from the strong fields of the magnets. So you can see for yourself just how strongly mu-metal attracts magnets (or vice versa) by taking apart a disk drive and separating the magnets from the shields.

The standard symbol for magnetic permeability is the italic Greek letter "mu" µ   which is where mu-metal gets its name.

[Nink]

Ni and Fe take a guess

[CANGAS]

Is mu-metal attracted to a magnet? No, but magnets are attracted to mu-metal...... Lol.




Sorry, couldn't resist. The actual answer to your question is YES, indeed. Mu-metal is a highly permeable nickel-iron-copper-chromium alloy which means it is actually more attracted to a magnet (or vice versa) than other alloys. You can think of it as "sucking in" as much magnetic flux as possible-- thus making the flux unavailable to do other things. Hence it acts as a "shield", not so much by "blocking" flux as by diverting it into itself.

Part of the process of making Mu-metal involves careful heat-treatments, hydrogen annealing which greatly increases the permeability, and this means that machining mu-metal, by milling, grinding, cutting and even bending, can reduce the "mu-ness" of it.

If you take apart a defunct computer hard disk drive, the very strong magnets in the head-positioning unit are attached to chunks of mu-metal that shield the disk itself from the strong fields of the magnets. So you can see for yourself just how strongly mu-metal attracts magnets (or vice versa) by taking apart a disk drive and separating the magnets from the shields.

The standard symbol for magnetic permeability is the italic Greek letter "mu" µ   which is where mu-metal gets its name.

Dear TinselKoala, your reply is thoroughly informative and very helpful. I give you my sincerest thank you.

At the risk of unintentionally offending you, for which I apologize in advance if such eventuates, I press you to tell me if you personally have "played" with mu metal and a magnet and have personally observed a momentum exchange between the magnet in your hand and the "lump" of mu metal on your workbench. I am in no position to invest in a portion of mu metal but find it of interest in my inventing adventures to know FOR CERTAIN if there is a momentum exchange involving a piece of mu metal and an adventurous magnet. And to know for sure if it is ATTRACTED or is REPELLED by an invading magnet.

Please forgive me for my aggressive questioning of you for this important information.


Great thanks to you
CANGAS 204

[TinselKoala]

Yes, I have. Take apart an old hard-drive and get your own pieces to play with!

It is _strongly_ attracted by magnets (or vice versa) not repelled. Too bad too, because if we could somehow come up with a true "shielding" material that was _not_ attracted, then some magnet motor designs might actually work (for certain values of "work". )

I can't find many good videos that show just how strongly mu-metal is attracted to magnets -- even dear old RG doesn't do a very good job, seems to have pretty much missed the point. Maybe this is because "magnet motor" builders want so much to believe that it isn't attracted, that it truly "shields" without sucking up the field within itself.


http://www.youtube.com/watch?v=RrwdeMCmdgM
http://www.youtube.com/watch?v=CeHkO_Y0Cjo