The bohr magneton is e hbar/ 2 m If we're talking about an electron in a metal or semiconductor, should the effective mass be used for m? From all the papers I've seen, nobody does that. They just use the free electron mass. For instance the Larmor precession of an electron moment. The frequency is g* mu_B B/hbar. I would assume that an effective mu_B should be used. Can anyone help?