GENERALIZED KITTEL-VAN VLECK RELATION BETWEEN G AND G' - VALIDITY FOR NEGATIVE G FACTORS

It is pointed out that a generalized exact relationship exists between the spectroscopic splitting factor g and the magnetomechanical ratio g for paramagnetic centers: g=g(g-) with =SzSz. Here S is the fictitious spin in the spin Hamiltonian and Sz is the expectation value of the real spin in the state labeled by Sz; the z axis is defined by the direction of magnetic field. Several classes of magnetic systems are considered, where for each system is constant over a wide range of physical parameters such as cubic crystal field and spin-orbit coupling, expressing an underlying symmetry of the magnetic ion in its environment. It is shown that the sole criterion for validity of the Kittel-Van Vleck relation g=g(g-1) is that Sz=Sz and that this may occur even when the admixed orbital angular momentum is very large so that the departure of g from 2 is very large. The generalized relation between g and g is also applied to cases where g is negative while g is positive. The extension of the relation between g and g to cases of interacting magnetic centers is discussed. © 1969 The American Physical Society.