Spin dynamics and magnetic phase diagram of La1-xCaxMnO3 (0 <= x <= 0.15) - art. no. 094405

Spin dynamics of ceramic La1-xCaxMnO3 with x = 0, 0.05, and 0.15 and the re lative Mn4+ concentration c = 0.18-0.22 is investigated by measurements of the ac susceptibility and the relaxation of the thermoremanent magnetizatio n (TRM). The chi (ac)(T) function exhibits a transition from the paramagnet ic to a mixed spin-glass and ferromagnetic phase. Below that is found a ste ep decrease and onset of the frequency dependence of chi (ac)(T), providing evidence for existence of a reentrant spin glass (RSG) phase. The dependen ce of the spin-glass freezing temperature, T-f, on f satisfies the conventi onal critical slowing-down law tau/tau (0) = (T-f/T-G - 1)(-zv) with tau = 1/f, zv = 12 +/- 2, tau (0) similar to 10(-12) s and the glass temperature, T-G, decreasing from 93 to 70.5 K when x is increased from 0 to 0.15. The relaxation rate S(t) of TRM has a clear maximum near a wait time t(w) simil ar to (2-4) x 10(3) s and the function S(T) shows a sharp maximum near T-G. The plots of S(T) exhibit a substantial decrease at T>T-G while for T<T-G they collapse into a single curve, as typical for mixed (T-G <T<T-C) and RS G phases, respectively. The observed spin dynamics agrees completely with t he magnetic phase diagram (paramagnetic, mixed, and RSG phases with decreas ing T) predicted recently for a system containing lattice disorder and comp eting superexchange and double exchange interactions.