Odd Magnet

[minesapint]

I've got a flat piece of magnetic material that measures 30mm long by 20mm wide and 3mm thick. You've all got something similar at home at it's the magnetic part of a broken fridge magnet.

I've discovered that curiously, the piece is only magnetic on one of the faces and I can't fathom out why. As I understood from my schoolboy physics, subjecting such a piece of material to a magnetic field would make it magnetic throughout. Yet one face of the piece does not adhere to metal at all.

The piece is definitely not two differing materials joined together as no seam is visible and the front and back faces look identical. The only difference in the two surfaces is that the back, non-magnetic, surface has two concentric rings embossed in the centre, one of the rings beings inside the other.

Could someone please explain what type of material this fridge magnetic could be made from and how it could be magnetic on one face only.

Many thanks.

[gen2]

This article explains most of it. I was looking for a page with a diagram but cannot find one.

http://www.madsci.org/posts/archives/1998-10/9 06639349.Ph.r.html

[minesapint]

Many thanks gen2 - you're a star!

The article cited does indeed demystify what I've seen. The only thing I'm a bit perplexed about is that the magnet is made from a hard, black, inflexible metallic-looking substance rather than moulded rubber - the thing sounds metallic when tapped on a metal surface.

I've got a couple of these moulded rubber type magnets on other fridge magnets and they don't look anything like the one I've been puzzling about.

Anyhow, thanks again.

[Billersand]

Magnets out of hard drives are "single sided" but I'm afraid I have no idea how it is achieved

[BillyBB]

I've ripped loads of magnets out of hard drives and they have all had a north and a south face.