Identifying a Magnet 1

[magneticrazy]

I pulled this magnet out of a hard drive that is well over 20 years old. I am having trouble identifying the material and type of magnet. Any thoughts? There is corrosion on all of the sides except the ones that weren't exposed to open air. They are still polished and reflective

 

[MagMike]

Most likely it is fully sintered NdFeB, but that is an odd shape (to me, at least). If it is nickel plated, then it is almost certainly NdFeB.
If it is unplated, then it probably is fully sintered SmCo.

Are you trying find a replacement magnet? If so, you'll probably have to send it to a reputable magnet vendor to determine the grade of material and magnetic pattern.

 

[EdStainless]

If it is over 20 years old then NdB is unlikely. Initial production was in the late '80s.
SmCo5 is most probable.
Atmospheric corrosion in 25 years would be expected. These are reactive materials.

Why are you interested?


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[MagnetDave]

It looks like a very early NdFeB magnet (as MagMike said). As he also said, if you want to determine anything useful, you need to go to a reputable vendor to have it tested to determine exactly what it is (in a functional sense) and how it can be replaced. We can perform a non-destructive (okay, reversible) test.

The color of the magnet indicates that it is nickel-plated, which supports the NdFeB theory. SmCo would not need to be plated.

However, it is still a weird shape - most hard drive voice coil magnets are thin arcs.

 

[drmagnet]

There are a few ways to tell the difference between magnetic materials. One is density: Neo is 7.5 g/cc, SmCo is 8.4 g/cc, Alnico is 7.3 g/cc. Ferrite is much lower density (4.9 g/cc) and also has the color and feel of a ceramic rather than a metallic gray color.

The magnet in the photo was not plated as most Neo magnets are now for use in hard drives. Plating would have remained shiny and the surface is more of a matte texture.

From the shape, I'd say this was from a tall drive, maybe 5 1/4 inch size and full height - something we no longer see.

Early Neo had a problem with oxidation and reaction with moisture to form Neo Hydroxide which is a bluish-gray powder that would be found on the magnet surface. So I'll vote with those who suggested SmCo.

 

[zanshangfeng]

Neodymium Magnets is very good ,And there is a large, is a big demand,From the shape and nature to tell him

 

[hacksaw]

regardless of the composition, be extremely careful with magnets that large, they can be very dangerous