MMM (moving magnetic material) record player cartridges ?

At your risk. A new name may create even more marketing confusion.

(summary: it is a small lightweight (small mass) magnetically permeable material that vibrates
By magnetic material is meant a magnetically permeable material and completes the magnetic flux circuit. Neither a moving magnet nor a moving coil since these are stationary inside the cartridge it may be called MMM. Small mass means easy acceleration.


A material which conducts a magnetic field. Analogous to a conductor conducting the electric field.


The term moving iron may be misleading (is magnetic reluctance the original term?), one may imagine something with a high mass moving along with the disc stylus.
Not nessesarily so.
The moving iron or magnetic permeable material may be just the cantilever itself. For example on some Stanton cartridges.
For example on the following patents:
US2538164 by Norman C. Pickering
US3546399 by Walter C. Stanton, Laurel Hollow


Low mass means faithful reproduction and minimal wear to record.


No wonder some Stanton cartridges go easily past 40KHz. [Stanton Product Catalogue]


There is similarly to ribbon mics. Just a length of material vibrating to sound. Of course the ribbon is so so much lighter.
On ribbon mics the signal voltage is taken from ribbon itself then feeding a transformer.
On MMM cartridges the signal voltage is taken from a stationary coil around magnetic circuit. In fact it may be thought as an impeded transformer so that the cartridge can feed an MC input or f
with  more coil turns of insulated fine wire an MM phono input.