Spin dynamics in perovskites, pyrochlores, and layered manganites

High temperature electron spin resonance (ESR) and magnetic susceptibility (chi) are analyzed for manganites related with colossal magnetoresistance ( CMR). The properties of compounds with different crystalline structures: th ree-dimensional (3D) perovskites, pyrochlore, and La1.2Sr1.8Mn2O7, a two-di mensional layer, are compared. In the paramagnetic regime, and outside the critical regions associated with phase transitions, the temperature depende nce of the ESR linewidth presents a universal behavior dominated by the var iations of chi(T), Delta H-pp(T)=[C/T chi(T)]Delta H-pp(infinity). The high temperature limit of the linewidth, Delta H-pp(infinity), is related to th e parameters of the Hamiltonian describing the interactions of the spin sys tem. The role played by magnetic anisotropy, isotropic superexchange, and d ouble exchange is revealed and discussed in the analysis of the experimenta l data. In CMR and non-CMR pyrochlores, Delta H-pp(infinity)proportional to omega(p)(2)/J where J is proportional to the Curie-Weiss temperature, incl uding the hybridization mechanism producing CMR. Instead, Delta H-pp(infini ty) of CMR perovskites seems not to be affected by the double-exchange inte raction. In contrast with the 3D perovskites, the ESR linewidth and resonan ce field of La1.2Sr1.8Mn2O7, a bilayer compound, although isotropic at high temperatures, becomes anisotropic for T-c=125 K < T < T(p)approximate to 4 50 K. (C) 2000 American Institute of Physics. [S0021-8979(00)42308-X].