Nature of the magnetic ground state in the A₁C₆₀ series

Anomalous metallicity and electronic phase separation in theCsC60polymerized fulleride

“…At the temperature of 13.8K the occurrence of a charge redistribution and a concomitant decrease of the local electronic susceptibility inside these nonmagnetic domains have been observed [11]. In agreement with this latter result, detailed analysis of the EPR linewidth at ambient pressure also suggest that two distinct magnetic environments coexist in the low temperature state of RbC 60 and CsC 60 polymers [12,13] and insofar as a charge redistribution occurs in the nonmagnetic domains at 13.8K [11], the spontaneous thermal contraction recently observed at 14K by X-Ray diffraction in CsC 60 [14] strongly supports the fact that these inhomogeneities are intrinsic.…”

“…As far as 133 Cs is concerned, 133 (T 1 ) −1 decreases linearly down to about 80K though remaining pressure independent up to 9kbar. This behavior is in sharp contrast with the 13 C nuclei for which 13 (T 1 ) −1 strongly decreases under pressure up to 9kbar while remaining almost temperature independent.…”

“…The measurements have been conducted on two powdered samples with entirely consistent results, one of them (10%) 13 C enriched. The pressure set up is a homemade double-stage copper-beryllium cell using fluor-inert as the pressure medium.…”

“…In addition, the low frequency conductivity of both RbC 60 and CsC 60 decreases smoothly over a broad temperature range, being at variance with KC 60 which remains conducting down to 4.2K [4]. Furthermore, the temperature dependence of the 13 C spin-lattice relaxation rate shows that strong magnetic fluctuations are present up to room temperature in RbC 60 and CsC 60 [5] and the sharp decrease of the uniform static susceptibility (measured from EPR line intensity) below 50K for RbC 60 and 40K for CsC 60 [4], suggests that both compounds undergo magnetic transitions at these respective temperatures. The occurrence of spin ordering is also evident from NMR experiments [5,6]: the slowing down of magnetic fluctuations gives rise to a divergent relaxation rate below 40K.…”

“…In this manuscript, we give experimental evidence showing that the "conducting" state of the CsC 60 polymerized phase cannot be understood within the framework of an electronic band conductor as claimed earlier [3][4][5]7,8,18] . We first report the temperature dependence of the spin lattice relaxation rate (T 1 ) −1 for both 13 C and 133 Cs nuclei at different pressures up to 9 kbar, indicating that in the temperature domain above 80K two different mechanisms govern the relaxation of 13 C and 133 Cs nuclei respectively. As far as 133 Cs is concerned, 133 (T 1 ) −1 decreases linearly down to about 80K though remaining pressure independent up to 9kbar.…”