where τ τ → → is the torque, μ μ → → is the magnetic dipole moment, J → → is the angular momentum vector, B → → is the external magnetic field, × × symbolizes the cross product, and γ γ is the gyromagnetic ratio which gives the proportionality constant between the magnetic moment and the angular momentum. The angular momentum vector J → → precesses about the external field axis with an angular frequency known as the Larmor frequency,