From: SFPhysics@aol.com
Date: Mon Apr 14 2003 - 12:20:47 PDT
From: SFPhysics@aol.com Message-ID: <76.2c86c461.2bcc640f@aol.com> Date: Mon, 14 Apr 2003 15:20:47 EDT Subject: Mapping Neodymium Magnets Fields
<< hello all,
>when looking at some
>small disc magnets, we notice that the field hardly
>represents a magnetic dipole.
>if anyone knows what's really happening with these
>super strong magnets, i'm sure we'd all be eager to
>learn. anything you know about how they are made,
>what the fields look like, how they can be so
>impossibly strong, etc. would be welcomed.
>thanks
>--eric
>>
Greetings Eric:
You are looking at two possible causes for an asymmetrical magnetic field
measurement. The first is that the magnets we find for the school science
labs are generally those which were surplus from the computer industry where
the magnets were manufactured for things like the stepper motors used to
position the reading heads of hard drives. They have deliberately shaped
magnetic fields that are not like bar magnets with fields being the same
shape at the north and south poles. Often they have a dispersed field on one
end and a concentrated field on the other end to facilitate the intended
motor operation.
The second possible factor giving you asymmetrical readings is that some of
the Hall sensors react differently to north and south poles where the fields
exceed a Gauss strength saturation for the device. Rare earth super magnets
can easily do this to Hall Effect sensors.
As to the question of why they are so strong, it is a function of
permeability, the magnetic flux density capacity. Air is considered as the
unity standard, Iron is much higher than air, and rare earth materials like
Neodymium, Gadolinium, etc., are the highest permeability's currently known.
To make the magnets the molten magnet metals are allowed to cool slowly
inside a very strong magnetic field. As the material crystallizes and drops
below the Curie Point the strong magnetic field is impressed on the
individual magnetic domains of the rare earth magnets. Because they are
essentially crystalline they will break easily when dropped or allowed to
bang into something else. When making an asymmetrical magnetic field, such
as you have found, the original applied magnetic field was also deliberately
shaped to concentrate one magnetic pole while allowing the other to have a
different shape that would be gathered by a ferromagnetic pole piece in the
intended device. When completely cool and hard the electromagnet inducing
the super magnets field is turned off and the super magnet retains its
phenomenal strength.
Hope that helps,
Al Sefl
Wishing for a magnetic personality but getting the equivalent of
diamagnetism...
Maybe Mapping Marvelous Manufactured Magnetic Moments Might Mess Messieurs
Meaningful Meticulous Measurements!
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