The motor force is exerted when two current carrying conductors are brought close together.
The force between two straight current carrying conductors is inversely proportional to their distance apart and proportional to their length and to the current. There is no magnetic field.
Consequently there is no need for any ferro-magnetic material to be inside the loops of wire. All the iron does is use up power. The force depends only on the current and the other parameters I mentioned.
So a motor is best made so the maximum force, when the conductors are close together, is exploited.
I did say "proportional" so there is the constant of proportionality which I think is the permeability of free space. In fact the force is electrostatic in nature, the so called magnetic field is the result of relativity length contraction. It is quite complicated to work out but it is only algebra.
What is wrong with Force=P*L*i/D where L>>D? P being the permeability of free space. L is the length, i the current, and D the perpendicular distance. I assume the conductors are parallel.
Actually putting an iron core into an electric motor only alters the impedance not the efficiency because power is lost in the iron which reduces efficiency.
A motor therefore needs to be long as well as fat because the long path means longer conductors and fat to increase the torque. A motor with no iron core is going to be a different size and shape to a normal one but may be lighter. To be compact it needs more windings.
Because the force between two current carrying conductors is electrostatic in nature the force for a particular current and motor construction may be increased by putting an electret between the conductors. Barium Titanate is a substance that can be used and this will increase the force around 10,000 times thus making the motor much more compact. It needs only to be put around the conductors around the periphery of the armature and the stator where the conductors are so that the clearance to allow rotation is small. None is needed inside the armature. A plastic ferrite could also be used or an normal ferrite. Or dust soft iron made into a paste with a resin.
This will make a small light motor.
The force between current carrying conductors is a consequence of special relativity, there is no magnetic field.
These motors were about to be made by Maia's company before she was brutally and forcibly leucotomised by psychiatrists for no reason that I can fathom out at all.
Another improvement is a copper casing outside the stator winding and inside the armature winding to screen the photons from leaving the motor compartment thus reducing loss still further.