How can I obtain a soft iron core for my electromagnet experiment?

[the_emi_guy]

Not the platter. The actuator contains two strong neodymium magnets mounted on mu-metal backer plates that block the strong magnetic field from appearing outside of the HD.

Here is a nice video of this that I found online:

 

[rbelli1]

They will also sometimes have a plate of it mounted above the platters. Sometimes internally, sometimes glued to the cover.

BoB