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Magnet properties

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Magnet properties

Unread postAuthor: saefroch » Sun Jul 10, 2011 9:35 pm

At dinner today I was asked to explain what B<sub>r</sub>, H<sub>c</sub>, and H<sub>ci</sub> are. I got the first two (reluctance and coercivity) down pretty well, but I'm completely lost on the third. This book seems to suggest that H<sub>ci</sub> doesn't exist, but this presentation seems to insist that it does, and that it differs from H<sub>c</sub>.

Can anyone explain H<sub>ci</sub> to me?
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Unread postAuthor: Mr.Tallahassee » Sun Jul 10, 2011 9:40 pm

"Hci Intrinsic coercive force of a material, < indicates its resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction, Bi, in the material to zero after magnetizing to saturation; measured in Oersteds" Found this at http://www.duramag.com/glossary.html I'm not certain myself.
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Unread postAuthor: Technician1002 » Sun Jul 10, 2011 10:21 pm

I think you are right. This property is important in setting AC bias levels for recording analog signals on magnetic tape. The other place you see this is when you order blank credit cards for use in access control to make employee cardlock badges. The low co material is easy to record, but was the early issue with credit cards and magnets. The high co mag stripe requires a much stronger field to erase it so common mistakes such as putting one in your billfold with someone's magnetic business card or stripe to stripe with another card won't erase it like it used to. Most credit card mag stripes are high co now.
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 10, 2011 10:23 pm

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Unread postAuthor: farmerboy32 » Mon Jul 11, 2011 10:43 am

hah jack you just made my morning!
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Unread postAuthor: saefroch » Mon Jul 11, 2011 12:03 pm

Mr.Tallahassee wrote:"Hci Intrinsic coercive force of a material, < indicates its resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction, Bi, in the material to zero after magnetizing to saturation; measured in Oersteds" Found this at http://www.duramag.com/glossary.html I'm not certain myself.
So how does H<sub>ci</sub> differ from H<sub>c</sub>????
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