RESUMEN
It is shown by electron paramagnetic resonance (EPR) and superconducting quantum interference device (SQUID) magnetometry that two spin systems coexist in conducting layers of the quasi-2D organic metal (BEDO-TTF)(2)ReO(4)·H(2)O: delocalized moments of charge carriers (holes), I(epr)(300 K) = 1.62 × 10(-4) emu mol(-1), and localized moments on BEDO-TTF(+1), χ(p)(300 K) = 4.25 × 10(-4) emu mol(-1). The phase transition Me-Me' at T(c) = 203 K is detected in paramagnetic relaxation, EPR amplitude and resistivity. Magnetic susceptibilities, I(epr) and χ(p), are not sensitive to the transition. Due to fine rearrangement of ReO(4) linked by H(2)O, the electronic spectrum becomes inhomogeneous. Below the transition exchange-coupled localized states within the metallic phase are observed. On cooling, the concentration of delocalized moments gradually decreases, contributing to a localized spin system. The phenomenon is interpreted in terms of short-range antiferromagnetic (AFM) interactions via conducting electrons. Below 14 K the AFM coupled states decay, and paramagnetism of local moments is recovered.
RESUMEN
The magnetization curves of Ca(1-x)(Ln)(x)MnO(3) single crystals, where Ln denotes La or Ce, x ≤ 0.12, have been measured in pulsed magnetic fields up to 350 kOe. The metamagnetic transitions for compositions with x = 0.10 and 0.12 have been observed in the temperature range 77-240 K. The hysteresis around the transition for the sweep-up and sweep-down branches of the magnetization curve is wide for x(Ce) = 0.10 and 0.12, and relatively narrow for x(La) = 0.12. The maximum magnetization value reaches ~50% from its theoretical value for x(Ce) = 0.10 and 0.12, and ~24% for x(La) = 0.12 in a magnetic field H = 350 kOe. The metamagnetic transition has been attributed to the melting of orbital/charge ordering in the dielectric antiferromagnetic C-type phase, which is accompanied by the growth of the volume of the conductive phase with antiferromagnetic G-type ordering and ferromagnetic contribution.