... are placed between the pole pieces of a strong magnet so that they are aligned along the direction of the field lines. Will they attract or repel each other?
Is this a joke? It sounds like the experiment where you tie buttered toast to a cat's back to see if the cat lands feet first or the toast lands buttered side down.
Paramagnetic means the material turns it's long dimension parallel to the field. Diamagnetic means the material turns its short dimension parallel to the field.
If the diamagnetic material is free to move, it will be thrust away from the field. No attraction.