Thermodynamic and transport properties of RAgGe (R=Tb-Lu) single crystals

TL;DR

This study reports on the synthesis, crystal structure, and magnetic and electronic properties of RAgGe (R=Tb-Lu) single crystals, revealing diverse magnetic behaviors, anisotropic metamagnetism, and potential quantum criticality in YbAgGe.

Contribution

It provides detailed characterization of the thermodynamic and transport properties of RAgGe compounds, highlighting the unique behavior of YbAgGe near a quantum critical point.

Findings

Antiferromagnetic ordering with T_N between 28.5 K and 1.0 K.

Observation of anisotropic metamagnetic transitions.

YbAgGe shows enhanced electronic specific heat and possible quantum criticality.

Abstract

Single crystals of the title compounds were grown out of an AgGe-rich ternary solution. Powder x-ray diffraction data confirmed the hexagonal AlNiZr-type structure ($P\bar{6}2m$ space group), an ordered variant of the Fe$_2$P structure type. Antiferromagnetic ordering can be inferred from magnetization, resistance and specific heat measurements, with values of T$_N$ between 28.5 K for TbAgGe, and 1.0 K for YbAgGe, which scale roughly with the de Gennes factor. Anisotropic $M(H)$ measurements indicate one or more metamagnetic transitions when the external field is applied along the c-axis (for R=Tb) or perpendicular to it (R = Ho, Er, Tm), or even in both orientations as in the case of DyAgGe. Furthermore, the extreme anisotropy of the magnetization in TmAgGe, where magnetic moments lie in the $ab$-plane, provides the possibility of studying the angular dependence of metamagnetism in hexagonal compounds with the rare earth in orthorhombic point symmetry. YbAgGe has distinct properties from the rest of the series: an enhanced electronic specific heat coefficient ($\gamma \approx$(154.2$\pm$2.5)mJ/mol*K$^2$), and apparently small moment magnetic ordering below 1.0 K. This compound appears to be close to a quantum critical point.