Hematite Magnets
Most recent answer: 10/22/2007
Q:
How would I go about magnetizing a real hematite bracelet? I know it is magnetic because I have big magnets that will pick up the bracelet but I can’t figure out how I would magnetize it.
- Rudy (age 18 )
San Diego, Ca, USA
- Rudy (age 18 )
San Diego, Ca, USA
A:
Rudy -
Good question. I know very little about hematite, so there's some guess work here, as you can see.
In scientific usage, hematite is a particular crystalline form of the compound Fe2O3 (2 iron atoms per 3 oxygen atoms). (Perhaps jewelers use the term differently.) At room temperature, this form is almost antiferromagnetic. If it were exactly antiferromagnetic, that would mean that the iron atoms (which themselves act like tiny magnets) would line up their magnetism in an alternating pattern, so that their magnetism would cancel. They actually tilt a little bit away from that pattern, so that they form a weak ferromagnet- a material which on its own forms magnetized domains, regions where the magnetism of the atoms adds up rather than cancels. When heated enough, hematite becomes a paramagnet, in which the atomic magnets just randomly point all different directions.
Anyway, although hematite is weakly magnetic (and hence can be attracted to your magnet), its magnetism is "soft", meaning that its domains don't stay lined up when the magnetic field is removed. In fact, the magnetic forces between the domains tend to make them line up opposite to each other. Some impurities in hematite can raise the strength of magnetization of its domains or increase their tendency to stay stuck once they are lined up. I've seen ads for magnetic hematite jewelry, so I suspect that it may contain such impurities.
It doesn't sound likely that you could magnetize your hematite much, but you could try warming it up and letting it cool in contact with your strongest magnet, just in case it has some domains that could get stuck lined up.
Mike W.
Good question. I know very little about hematite, so there's some guess work here, as you can see.
In scientific usage, hematite is a particular crystalline form of the compound Fe2O3 (2 iron atoms per 3 oxygen atoms). (Perhaps jewelers use the term differently.) At room temperature, this form is almost antiferromagnetic. If it were exactly antiferromagnetic, that would mean that the iron atoms (which themselves act like tiny magnets) would line up their magnetism in an alternating pattern, so that their magnetism would cancel. They actually tilt a little bit away from that pattern, so that they form a weak ferromagnet- a material which on its own forms magnetized domains, regions where the magnetism of the atoms adds up rather than cancels. When heated enough, hematite becomes a paramagnet, in which the atomic magnets just randomly point all different directions.
Anyway, although hematite is weakly magnetic (and hence can be attracted to your magnet), its magnetism is "soft", meaning that its domains don't stay lined up when the magnetic field is removed. In fact, the magnetic forces between the domains tend to make them line up opposite to each other. Some impurities in hematite can raise the strength of magnetization of its domains or increase their tendency to stay stuck once they are lined up. I've seen ads for magnetic hematite jewelry, so I suspect that it may contain such impurities.
It doesn't sound likely that you could magnetize your hematite much, but you could try warming it up and letting it cool in contact with your strongest magnet, just in case it has some domains that could get stuck lined up.
Mike W.
(published on 10/22/2007)
Follow-Up #1: 'Oidz' Magnets
Q:
I’m confused by the claim of a number of magnetic toys, going by numerous brand names, most commanly ’oidz,’ which claim to be made from hematite:
http://www.play.com/Gadgets/Gadgets/4-/852389/Oidz/Product.html
http://www.iwantoneofthose.com/uberorbs/index.html
I don’t believe this is a typo or anything (even tho they do refer to hematite as a ’metal’), as it seems to be quite consistently claimed in a bunch of places on t’internet
cheers
mike
x x x
- Mike Pledger (age 23)
Wales, UK
- Mike Pledger (age 23)
Wales, UK
A:
By coincidence, an eccentric cousin-in-law gave my family a couple of sets of these. By an even weirder coincidence, I was able to find them just now. I can't measure any electrical conductivity across them, even when I try scratching through any possible insulating surface. So they sure don't seem to be metals. Probably whoever first wrote that merchandising blurb (the sites seem to copy from a single source) wasn't motivated to use precise scientific language.
These things do seem to be pretty strong magnets, as judged by the paperclip test, i.e. how long a chain of paperclips they can hold up. (I'm at home right now, so there's no fancy Gaussmeter available.) Whether that means they aren't really pure hematite, I'm not sure. It wouldn't be surprising if they contained a mixture of different iron oxides, some of which are more magnetic.
Probably the most important lesson here is that no matter how much something is "consistently claimed in a bunch of places on t’internet", there’s no reason to trust those sites. It’s even easier to cut and paste than to measure with an ohmmeter.
Mike W.
These things do seem to be pretty strong magnets, as judged by the paperclip test, i.e. how long a chain of paperclips they can hold up. (I'm at home right now, so there's no fancy Gaussmeter available.) Whether that means they aren't really pure hematite, I'm not sure. It wouldn't be surprising if they contained a mixture of different iron oxides, some of which are more magnetic.
Probably the most important lesson here is that no matter how much something is "consistently claimed in a bunch of places on t’internet", there’s no reason to trust those sites. It’s even easier to cut and paste than to measure with an ohmmeter.
Mike W.
(published on 10/22/2007)
Follow-Up #2: hematite vs. ferrite
Q:
The so called "magnetic hematite" is a synthetic ferrite. It looks like hematite when it is polished, but has a different composition and crystal structure.
- Howard
Yonkers, NY USA
- Howard
Yonkers, NY USA
A:
Aha- That would explain why things called 'hematite' are more magnetic than one would expect. Do you have a reference for that?
Mike W.
Mike W.
(published on 04/20/2010)
Follow-Up #3: more "hematite" info
Q:
http://www.mindat.org/min-35948.html Generally, true Hematite is not magnetic. Hemalyke and hematine are imitation hematite that is magnetic. This is one source I found. I have seen several sources that say the same thing like you posted earlier. It generally is barely magnetic if at all. If it has a perceptible magnetism, it ain't hematite. I bet you already knew that though. ;)
- E Smith
Conroe, Tx USA
- E Smith
Conroe, Tx USA
A:
Thanks!
Mike W.
Mike W.
(published on 07/16/2010)