Magnon-induced pseudoquadrupole interaction in ordered systems

Temperature-dependent aspects of the Suhl-Nakamura process, contributing to the measured quadrupole interaction in ordered systems, are described. The mechanism involves a pseudoquadrupolar coupling of magnons with nuclei via the magnetic hyperfine or transfered hyperfine IzSz interaction. Within the framework of the long-wave magnon approximation, the process is linear in the magnetization and explains recent experimental results for Al27 in GdAl2. A simple method of utilizing the new mechanism for the sign determination of the electric field gradient q is described, and the method is applied to determine q<0 at the Al sites in GdAl2. Various implications of the new process are briefly discussed.