ELECTRON SPIN RESONANCE AS A PROBE OF COLLECTIVE MODES IN ANISOTROPIC EXCHANGE-COUPLED PARAMAGNETS

Abstract

Electron spin resonance (ESR) in exchanged-coupled paramagnets is a probe of field-dependent collective modes in a strongly coupled many-body system. We utilize a previously developed approach for the analysis of collective modes in such systems to express the experimentally determined g-factors of the ESR modes in an anisotropic magnet in terms of the microscopic (isolated spin) g-factors and the ratios of the static susceptibilities along the principal directions. Applications of the theory to the ferromagnetic insulator CrBr 3 and the Kondo lattice systems YbRh 2 Si 2, YbCo 2 Si 2, YbIr 2 Si 2 and CeRuPO are discussed.