Dynamic Effect of Low-Symmetric Distribution of Spins on EPR Lines in One-Dimensional Magnetic Systems. I. Theory and Experiment in TMMC

Abstract

The Kubo-Tomita theory which stands on the assumption of high symmetry of the perturbation is extended so as to discuss EPR of systems with low-symmetric perturbation of dipolar interaction such as the case of TMMC, The extended formula which includes a new term arising from the one-dimensionality, of spin arrangement is developed for second cumulant of correlation function ⟨M_x(t)M_x(0)⟩ of the magnetization. This term causes a new dynamic shift δH of resonance field expressed as δH∝−sin² θ(3 cos² θ−1) cos 2φ. (Here, θ and φ are the polar and azimuthal angles, respectively, of the chain axis in the coordinate system where the direction or static field is taken as the polar axis.) New measurements changing φ as well as θ have been performed in TMMC. Observed features coincide well with the present theoretical predictions.