Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM$_2$Al$_{20}$ [R = Eu,Gd and La ; TM = V,Ti]

TL;DR

This study investigates the magnetic, thermal, and electrical properties of single-crystal Frank-Kasper compounds RTM$_2$Al$_{20}$, revealing first-order magnetic transitions, double magnetic transitions, and Fermi liquid behavior across different R and TM elements.

Contribution

It provides new insights into the magnetic phase transitions and thermal properties of RTM$_2$Al$_{20}$ compounds, highlighting their first-order transitions and double magnetic transitions.

Findings

Observation of first-order magnetic transitions in Eu/GdTi$_2$Al$_{20}$.

Detection of double magnetic transitions indicated by susceptibility and heat capacity.

All compounds exhibit Fermi liquid behavior in electrical resistivity.

Abstract

Single crystals of Frank-Kasper compounds RTM$_2$Al$_{20}$ (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 $Fd\overline{3}m$. The magnetic susceptibility for the compounds EuTi$_2$Al$_{20}$ and GdTi$_2$Al$_{20}$ showed a sudden jump below the N{\'e}el 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)Ti$_2$Al$_{20}$ compounds Full width at half-maximum (FWHM) $<$ 0.2 K) which is reminiscent of a first-order phase transition and a unique attribute among RTM$_2$Al$_{20}$ compounds. We observed clear anomaly between heating and cooling cycle in temperature-time relaxation curve for the compounds GdTi$_2$Al$_{20}$ (2.38 $K$) and EuTi$_2$Al$_{20}$ (3.2 $K$) which is indicating a thermal arrest due to the latent heat. The temperature variation of $S_{mag}$ for GdTi$_2$Al$_{20}$ saturates to a value $0.95R\ln8$ while the other magnetic systems exhibited still lower entropy saturation values in the high temperature limit. Resistivity measurements showed that all the samples behave as normal Fermi liquid type compounds and $\rho(T)$ due to electron-phonon scattering follows Bloch-Gr$\ddot{\textrm u}$neisen-Mott relation in the paramagnetic region.