Can diamagnetic materials or a diamagnetic devise be used to propel using the magnetic field of the Sun in a solar polar magnetic assisted slingshot?
What you are looking for is an electrodynamic tether. The wikipedia article goes quite into detail so I won't repeat everything here.
The short version is: Have a long conductor protruding from your space craft (The tether). If you apply direct current to the tether a Lorentz force is exerted against the surrounding magnetic field. With this you can brake or accelarate. You could even use this for interstellar travel. Although you won't get high rates of acceleration you have the advantage of not needing to carry a large tank of propellant. Many satellites already use this technology to alter their orbit but currently there are no missions planned to use this for interplanetary or even interstellar travel
While CKA gives the right idea, it's not practically possible currently.
Many satellites use magnetorquers, which apply torque orienting the satellite in the right orientation. For applying current, you need a circuit, which forms a loop - and you're getting zero net thrust as there's the same amount of current going "up" as "down". As you can have these two streams go through two different parts of satellite, you can have two opposing forces with different points of application - torque. This is useful for attitude control, but provides no propulsion whatsoever.
For propulsion, you need an open circuit, current traveling down the tether without going back. And that pretty much immediately creates a difference of potential which stops the current dead. To remove that difference of potential without sending current back the same (or similar) route you need to emit electrons into vacuum at one end, positive ions (or capture electrons from space) at the other. And these emitters have a very low efficiency - you're getting microamperes of current, and so the resulting force is minuscule, definitely not enough for interplanetary propulsion; not even enough for regular station-keeping.
The same applies to Sun's magnetic field. And even the lightest positive ions (protons; hydrogen nuclei) would be better spent as regular propellant so unless we develop means to efficiently capture and discard large amounts of electrons, electrodynamic tether remains another of these "looks good on paper" ideas.