Modified spin-wave theory of nuclear magnetic relaxation in one-dimensional quantum ferrimagnets: Three-magnon versus Raman processes

TL;DR

This paper investigates nuclear magnetic relaxation in one-dimensional quantum ferrimagnets using a modified spin-wave theory, revealing that three-magnon processes can dominate over Raman processes at higher temperatures and lower magnetic fields.

Contribution

It introduces a modified spin-wave theoretical approach that accounts for higher-order interactions, showing the dominance of three-magnon relaxation mechanisms in certain conditions.

Findings

Three-magnon relaxation can surpass Raman processes at high temperatures.

Exchange-scattering enhances three-magnon nuclear relaxation.

Experimental data on NiCu chain supports the theoretical prediction.

Abstract

Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is studied by means of a modified spin-wave theory. Calculating beyond the first-order mechanism, where a nuclear spin directly interacts with spin waves through the hyperfine coupling, we demonstrate that the exchange-scattering-enhanced three-magnon nuclear relaxation may generally predominate over the Raman one with increasing temperature and decreasing field. Recent proton spin-lattice relaxation-time (T_1_) measurements on the ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O suggest that the major contribution to 1/T_1_ be made by the three-magnon scattering.