[the modulator]

I might have to clean the innards of this cartridge. I’d like to read into this before I move forward. First off, I don't know what part of the cartridge this is called. "This" being the metal parts inside the red circle in the picture. I believe it’s the magnet, but I’m not sure. What is it?
 
Has anyone cleaned this area out before? I saw it under a microscope and it’s dirty. Should I clean this area out?
 
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