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Characterising neodymium magnets

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james_s:
Would heating still spoil the plating if done in an inert environment? Pyrex tube flushed with argon or something might do the trick.

ejeffrey:
I would definitely be looking at isolating the cause better:  the magnet, the iron, or the magnetization procedure.

Can you safely (but destructively) remove the magnets from a system?  Pull one out and compare it's magnetic field to that of a known good magnet.  You should be able to see if the field is weaker or in a different direction.

Annealing and remagnetizing might destroy the nickel coating, but it would still be worth trying on a reject to see if it magentized properly the second time.  That would indicate a problem with the magnetization protocol.

Alternately: you can't degauss them and you can't heat them up to the curie point without destroying them, maybe you can do a combination.  Heat them up to 150-200C and then try to degauss?  I'm not at all an expert in rare earth magnets, but I would expect it becomes easier to demagnetize even well below the curie point.

thm_w:

--- Quote from: ejeffrey on March 03, 2023, 07:31:43 pm ---Alternately: you can't degauss them and you can't heat them up to the curie point without destroying them, maybe you can do a combination.  Heat them up to 150-200C and then try to degauss?  I'm not at all an expert in rare earth magnets, but I would expect it becomes easier to demagnetize even well below the curie point.

--- End quote ---

The link I posted above used 200C, which should be fine for the plating.

"This temperature is considerably lower than the Curie Temperature of about 300 °C, illustrating that heating above the Curie temperature is not needed to obtain 90% demagnetization."

hanakp:
If you confirm there is a probem with the magnets themselves, there is a way to quickly and non-destructively check their elemental composition, but you won't like it. It's called X-ray fluorescence spectrometry and there are even handheld "guns" that can do it. But they're quite expensive and you need to observe rather stringent ionizing radiation precautions around them. In your case, even small flaws in elemental composition may cause the problem. Thus you may need a full-sized cabinet XRF machine, which have higher sensitivity, but are even more expensive than the "guns".

james_s:
I saw one of those at a scrap metal dealer once. He didn't seem to be exercising any particular caution, he was just pointing it at various objects to check the composition. I think the xray dose produced by them is very low. Neat gadget, about the closest thing we have to a Tricorder in real life.

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