We report electron spin resonance (ESR) measurements in the Gd3+ doped semiconducting filled skutterudite compound Ce1-xGdxFe4P12 (x = 0.001). As the temperature T varies from T = 150 K to T = 165 K, the Gd3+ ESR fine and hyperfine structures coalesc
e into a broad inhomogeneous single resonance. At T = 200 K the line narrows and as T increases further, the resonance becomes homogeneous with a thermal broadening of 1.1(2) Oe/K. These results suggest that the origin of these features may be associated to a subtle interdependence of thermally activated mechanisms that combine: i) an increase with T of the density of activated conduction-carriers across the T-dependent semiconducting pseudogap; ii) the Gd3+ Korringa relaxation process due to an exchange interaction, J_{fd}S.s, between the Gd3+ localized magnetic moments and the thermally activated conduction-carriers and; iii) a relatively weak confining potential of the rare-earth ions inside the oversized (Fe2P3)4 cage, which allows the rare-earths to become rattler Einstein oscillators above T = 148 K. We argue that the rattling of the Gd3+ ions, via a motional narrowing mechanism, also contributes to the coalescence of the ESR fine and hyperfine structure.
We report evidence for a close relation between the thermal activation of the rattling motion of the filler guest atoms, and inhomogeneous spin dynamics of the Eu2+ spins. The spin dynamics is probed directly by means of Eu2+ electron spin resonance
(ESR), performed in both X-band (9.4 GHz) and Q-band (34 GHz) frequencies in the temperature interval 4.2 < T < 300 K. A comparative study with ESR measurements on the Beta-Eu8Ga16Ge30 clathrate compound is presented. Our results point to a correlation between the rattling motion and the spin dynamics which may be relevant for the general understanding of the dynamics of cage systems.
In this work we report electron spin resonance (ESR) measurements in the semiconducting Ce1-xGdxFe4P12 (x ~ 0.001) filled skutterudite compounds. Investigation of the temperature (T) dependence of the ESR spectra and relaxation process suggests, that
in the T-interval of 140-160 K, the onset of a weak metal-insulator (M-I) transition takes place due to the increasing density of thermally activated carriers across the semiconducting gap of ~ 1500 K. In addition, the observed low-T fine and hyperfine structures start to collapse at ~ 140 K and is completely absent for > 160 K. We claim that the increasing carrier density is able to trigger the rattling of the Gd3+ ions which in turn is responsible, via a motional narrowing mechanism, for the collapse of the ESR spectra.
We give an extensive treatment of the pairing symmetry in the ferromagnetic superconductor $UGe_{2}$. We show that one can draw important conclusions concerning the superconducting state, considering only the transformation properties of the pairing
function, without assumptions about the form of the pairing amplitudes.
Electron Spin Resonance (ESR) measurements performed on the filled skutterudite system Ce1-x$YbxFe4P12 (x< 0.003) unequivocally reveal the coexistence of two Yb3+ resonances, associated with sites of considerably different occupations and temperature
behaviors. Detailed analysis of the ESR data suggests a scenario where the fraction of oversized (Fe2P3)4 cages that host Yb ions are filled with a low occupation of on-center Yb3+ sites and a highly occupied T-dependent distribution of off-center Yb3+ sites. Analysis of the 171Yb3+ (I=1/2) isotope hyperfine splittings reveal that these two sites are associated with a low (~ 1 GHz) and a high (> 15 GHz) rattling frequency, respectively. Our findings introduce Yb3+ in Th symmetry systems and uses the Yb3+ ESR as a sensitive microscopic probe to investigate the Yb3+ ions dynamics.
Despite extensive research on the skutterudites for the last decade, their electric crystalline field ground state is still a matter of controversy. We show that Electron Spin Resonance (ESR) measurements can determine the full set of crystal field p
arameters (CFPs) for the Th cubic symmetry (Im3) of the Ce$_{1-x}$R$_{x}$Fe$_{4}$P$_{12}$ (R = Dy, Er, Yb, $xlesssim 0.003$) skutterudite compounds. From the analysis of the ESR data the three CFPs, B4c, B6c and B6t were determined for each of these rare-earths at the Ce$^{3+}$ site. The field and temperature dependence of the measured magnetization for the doped crystals are in excellent agreement with the one predicted by the CFPs Bnm derived from ESR.
