Anisotropic Evolution of the Spin-Triplet States Under the Action of the Varying Fields and the Lattice in a Nonzero Constant Field

The equations of motion of the magnetization components related to the separate transitions of the EPR fine structure (FS) of the spin-triplet states (STS) under the action of the constant and alternating fields in the case of a nonzero constant field are derived. It is demonstrated that at the definite condition fulfillment, the free motion of the sample magnetization after the excitation of one of the FS transitions is the precession at the frequency of the excited transition with an ellipse in the plane transverse to the constant field. The tensor of the dynamic susceptibility of the spin-system (SS) to the microwave field is provided for the creation of the resonance conditions for each transition of the well-resolved FS. The possibility of the elliptical character of the magnetization precession at the steady-state excitation by the transverse varying field is revealed. The rate of the one-phonon spin-lattice relaxation (SLR) is obtained under conditions, when SS is described by a single spin temperature. At that, the possibility of the presence of the fast motion in the SS is provided for. The SLR rates of the separate transitions of the FS are calculated at the same one-phonon mechanism.