Reciprocating thermal behavior in a magnetic field induced slow spin relaxation of [Gd-2(H2O)(6)(C2O4)(3)]center dot 2.5H(2)O

Static and alternating magnetic susceptibility, magnetization, and electron-spin resonance studies of Gd(III) complex [Gd-2(H2O)(6)(C2O4)(3)]center dot 2.5H(2)O enabled its identification as an S = 7/2 magnet with easy-axis anisotropy D/kB = -91.2 mK and magnetic interaction effectively mediated by dipolar coupling |J/kB| approximate to 12 mK. The magnetic field-induced slow relaxation at high temperatures is ascribed to direct relaxation with a pronounced effect of phonon bottleneck and Raman process. In contrast, relaxation at low temperatures displays recipro-cating thermal behavior, where spin dynamics accelerates upon cooling. The potential origin of the observed behavior is discussed.