Frank-Kasper笼状化合物RTM PDMATHAAC Al $_{20}$ [R = Eu，Gd，La ; TM = V，Ti]的磁、specific heat和电输运性质
Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM$_2$Al$_{20}$ [R = Eu,Gd and La ; TM = V,Ti]
摘要：
用自熔法生长了Frank-Kasper化合物RTM $_2$ Al $_{20}$（R = Eu，Gd，La; TM = V，Ti）的单晶，并通过测量磁化率（$M$）、磁化率（$χ$）、比热（$C_P$）和电阻率（$ρ$）研究了它们的物理性质。粉末X-射线衍射研究和结构分析表明，这些化合物结晶在立方晶体结构与空间群$Fd\overline{3}m$。化合物EuTi $_2$ Al $_{20}$和GdTi $_2$ Al $_{20}$的磁化率显示出低于N{é}el温度$T_N$的突然跳变，指示合理的双磁转变。比热（$C_P$）和电阻率（$ρ$）的测量也证实了一阶磁转变（FOMT）和可能的双磁转变。热容的温度变化显示出（Eu/Gd）Ti $_2$ Al $_{20}$化合物的急剧相变和巨大的$C_P$值（半峰全宽（FWHM）$<$ 0.2 K），这使人想起一级相变和RTM $_2$ Al $_{20}$化合物中的独特属性。我们在化合物GdTi $_2$ Al $_{20}$（2.38 $K$）和EuTi $_2$ Al $_{20}$（3.2 $K$）的温度-时间弛豫曲线中观察到明显的加热和冷却循环之间的异常，这表明由于潜热引起的热停滞。对于GdTi $_2$ Al $_{20}$的$S_{mag}$的温度变化饱和到一个值$0.95R\ln8$，而其他磁系统在高温极限下表现出更低的熵饱和值。电阻率测量表明，所有样品均表现为正常的费米液体型化合物，在顺磁区，由于电子-声子散射引起的$ρ(T)$符合Bloch-Gr $\ddot{\textrm u}$ neisen-Mott关系。
英文摘要：
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 ($χ$), specific heat ($C_P$) and electrical resistivity ($ρ$) 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{é}el temperature $T_N$ indicative of plausible double magnetic transition. Specific heat ($C_P$) and electrical resistivity ($ρ$) 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 $ρ(T)$ due to electron-phonon scattering follows Bloch-Gr$\ddot{\textrm u}$neisen-Mott relation in the paramagnetic region.
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