What materials can increase magnetic strength in an electromagnetic coil?

[Phaedrus]

I realize that soft iron is the most common material for this but I am wondering if there is something that will increase the magnetic strength.
Here is what I have.
Two electromagnetic coils in series connected by a yoke with a capacitor in parallel (for spark reduction). Cores are soft iron 3/8" or 5/16" x 1 1/4". The magnets move an armature bar that switches the circuit on/off 80-160 Hz.

I'm am looking for a material that will create a stronger magnetic field without having to increase voltage (3-9 volts DC < 1amp) .

What would the most efficient materials be that are available in those dimensions if one were willing to spend more $.

 

[dean125]

Are you asking this to improve the magnetic strength of the electromagnetic cores of a tattoo machine?

 

[FredGarvin]

Have you tried contacting any solenoid manufacturers to see if anything is commercially available?

 

[stewartcs]

Magnetite (Fe3O4 - Ferrous-Ferric Oxide).

http://en.wikipedia.org/wiki/Magnetite