Pyrochlore manganites spin dynamics in the paramagnetic regime

We report electron spin resonance (ESR) and dc magnetic susceptibility in p olycrystalline pyrochlores A(2)Mn(2)O(7) (A = Y, Tl) measured in the parama gnetic phase up to 600 K. It is shown that the ESR linewidth has a universa l behavior given by Delta H-pp(T) = Delta H-pp (T --> infinity) [ C/T chi(d c)(T)], where C is the single-ion Curie constant. The high-temperature limi t for the linewidth, given by Delta H-pp(T --> infinity)proportional to(ome ga(p))(2)/J, is determined by the superexchange constant J for each materia l. A value of (omega(p)/gamma) = 6300 G was found for all pyrochlores, incl uding In2Mn2O7. Different broadening mechanisms are discussed. (C) 1999 Ame rican Institute of Physics. [S0021-8979(99)25608-3].