Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM2Al20 [R = Eu, Gd and La; TM = V, Ti]

摘要

Single crystals of Frank-Kasper compounds RTM2Al20 (R = Eu, Gd and La; TM = V and Ti) were grown by self-flux method and their physical properties were investigated through magnetization (M), magnetic susceptibility (chi), specific heat (C-P) and electrical resistivity (rho) measurements. Powder x-ray diffraction studies and structural analysis showed that these compounds crystallize in the cubic crystal structure with the space group Fd (3) over barm. The magnetic susceptibility for the compounds EuTi2Al20 and GdTi2Al20 showed a sudden jump below the Neel temperature T-N indicative of plausible double magnetic transition. Specific heat (C-P) and electrical resistivity (rho) measurements also confirm the first-order magnetic transition (FOMT) and possible double magnetic transitions. Temperature variation of heat capacity showed a sharp phase transition and huge C-P value for the (Eu/Gd)Ti2Al20 compounds' full width at half-maximum (FWHM) (<0.2 K) which is reminiscent of a first-order phase transition and a unique attribute among RTM2Al20 compounds. In contrast, linear variation of CP is observed in the ordered state for (Eu/Gd)V2Al20 compounds suggesting a lambda type transition. We observed clear anomaly between heating and cooling cycle in temperature-time relaxation curve for the compounds GdTi2Al20 (2.38 K) and EuTi2Al20 (3.2 K) which is indicating a thermal arrest due to the latent heat. The temperature variation of S-mag for GdTi2Al20 saturates to a value 0.95Rln 8 while the other magnetic systems exhibited still lower entropy saturation values in the high temperature limit. (CP - gamma T)/T-3 versus T plot showed a maximum near 27 K for all the compounds indicating the presence of low frequency Einstein modes of vibrations. Resistivity measurements showed that all the samples behave as normal Fermi liquid type compounds and rho(T) due to electron-phonon scattering follows Bloch-Grueisen-Mott relation in the paramagnetic region.