The outer rotor appears to be just a light alloy diecasting, and is rigidly fixed to the 4mm dia spindle. No sign of any permanent magnets.
My best guess is some sort of control device, a current through one winding induces a current in the second which will vary as the outer rotor is turned. Any better or more detailed ideas? I've landed myself with a number of them as part of a job lot.
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service