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.

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

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

i agree with some of that, mu metal is not fully dielectric material.
it will try react just like regular metal, however it does allow some shielding, or  shape control of a field.
it could be used to help regulate the strength of a magnets polar region.

Ok in short the answer you where looking for is yes MU Metal attract magnets and it's truely crap in almost all senses possible, here's why: first of all One sheet that is like .032mm or so still cost a freaking fortune (the less pricy i saw is on Ebay up to now but i have no idea of the quality). And these ridiculously super ultra thin sheets needs at least 10 sheets thick to cover about any regular size neo magnets so again, a real little fortune. Not to mention that there's a special treatment made on these sheets, if they are bent it breaks that protection where it has bent so the other guy who received his sheets all ready bent in the package definitely got scammed. when it's bent it would need to be retreated again witch if i remember correctly takes 4 hours at 400 degrees celcius. And maybe some other thing I do not remember but anyway it's a true lost of time and money.

IF you want materials that shields a little AND do not stick at all is 316L stainless steel. the L stands for Low carbon you could ask for 316H but it's only for welders and will not change a darn thing.
A full sheet of 4 feet by 8 feet at around 1/16 thick cost quite a fortune but i'm sure you can find companies that do stainless and could sell you small amounts of materials for mire nothing... Like for 40$ or so you could have enough materials to build your thing. If you arrive with precise dimensions you can even ask them to bend it like you want for a little extra. But you must have a physical drawing with exact and clear dimensions on it. And if you need it to be ultra precise you'll need the radius of the bent also. Should all be around 100$ max. that steel let magnetism through a little bit less then regular steel but it has the advantage of not being sticky with magnets. Bring a magnet with you when you ask for 316L they may not know if they have it or not. Hope it helped.

N.B. You could make a search locally arround your place for stainless welders Or something similar. any restaurant kitchen counter is normally also made from stainless so maybe they have some too. Or can get you some and when your there if they don't have any from there you can ask for other sources. and if everything fails there's always this alternative... they do custom shielding for a little over 60 years for eletrical engineers and guys like you and me... they are not cheap though but it's worth it if you know what your doing : http://www.magnetic-shield.com/request-for-quote.html

What happens at or around the point of saturation?

At saturation, the attraction stops increasing.

Also, since mu-metal is electrically conductive, it will be repelled by eddy currents if a permanent magnet's pole is moved towards it very quickly.