Ramesh Kumar K, Nair Harikrishnan S, Christian Reinke, Thamizhavel A, Strydom André M
Highly Correlated Matter Research Group, Physics Department, PO Box 524, University of Johannesburg, Auckland Park 2006, South Africa.
J Phys Condens Matter. 2016 Nov 2;28(43):436002. doi: 10.1088/0953-8984/28/43/436002. Epub 2016 Sep 7.
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 (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 [Formula: see text]. The magnetic susceptibility for the compounds EuTi2Al20 and GdTi2Al20 showed a sudden jump below the Néel 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)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 C P is observed in the ordered state for (Eu/Gd)V2Al20 compounds suggesting a λ-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 [Formula: see text] while the other magnetic systems exhibited still lower entropy saturation values in the high temperature limit. [Formula: see text] 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 [Formula: see text] due to electron-phonon scattering follows Bloch-Grüneisen-Mott relation in the paramagnetic region.
采用自熔剂法生长了Frank-Kasper化合物RTM2Al20（R = Eu、Gd和La；TM = V和Ti）的单晶，并通过磁化强度（M）、磁化率（χ）、比热（CP）和电阻率（ρ）测量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，这些化合物以空间群为[公式：见原文]的立方晶体结构结晶。EuTi2Al20和GdTi2Al20化合物的磁化率在奈尔温度TN以下出现突然跃升，表明可能存在双重磁转变。比热（CP）和电阻率（ρ）测量也证实了一级磁转变（FOMT）和可能的双重磁转变。热容随温度的变化显示，（Eu/Gd）Ti2Al20化合物的半高宽（FWHM）（<0.2 K）处有尖锐的相变和巨大的CP值，这让人联想到一级相变，是RTM2Al20化合物中的一个独特属性。相比之下，（Eu/Gd）V2Al20化合物在有序状态下观察到CP的线性变化，表明是λ型转变。我们在GdTi2Al20（2.38 K）和EuTi2Al20（3.2 K）化合物的温度-时间弛豫曲线中观察到加热和冷却循环之间明显的异常，这表明由于潜热导致了热停滞。GdTi2Al20的S磁随温度的变化在高温极限下饱和到一个值[公式：见原文]，而其他磁系统表现出更低的熵饱和值。[公式：见原文]与T的关系图显示，所有化合物在27 K附近出现最大值，表明存在低频爱因斯坦振动模式。电阻率测量表明，所有样品都表现为正常费米液体型化合物，并且由于电子-声子散射，[公式：见原文]在顺磁区域遵循布洛赫-格律内森-莫特关系。
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