Anisotropic magnetization, specific heat and resistivity of RFe2Ge2 single crystals

TL;DR

This study synthesizes high-quality RFe2Ge2 single crystals across the lanthanide series, revealing strong magnetic anisotropies, antiferromagnetic orderings, and electronic properties, with implications for understanding magnetic and electronic behaviors in these compounds.

Contribution

It provides a comprehensive characterization of RFe2Ge2 single crystals, including growth methods, anisotropic magnetic properties, and electronic behavior, highlighting the effects of crystal field and rare earth elements.

Findings

Strong anisotropies mainly due to CEF effects observed.

Antiferromagnetic ordering temperatures scale with de Gennes factor.

Y and Lu members show large electronic specific heat and density of states.

Abstract

We have grown RFe2Ge2 single crystals for R = Y and ten members of the lanthanide series (Pr, Nd, Sm, Gd-Tm, Lu) using Sn flux as the solvent. The method yields clean, high quality crystal plates as evidenced by residual resistivities and RRR values in the range of 3-12 uOhm cm and 20-90 respectively. The crystals are also virtually free of magnetic impurities or secondary phases, allowing the study of the intrinsic anisotropic magnetic behavior of each compound. Characterization was made with X-Ray diffraction, and temperature and field dependent magnetization, specific heat and resistivity. Very strong anisotropies arising mostly from CEF effects were observed for all magnetic rare earths except Gd. Antiferromagnetic ordering occurred at temperatures between 16.5 K (Nd) and 1.1 K (Ho) that roughly scale with the de Gennes factor for the heavy rare earths. For some members there is also a lower temperature transition associated with changes in the magnetic structure. Tm did not order down to 0.4 K, and appears to be a van Vleck paramagnet. All members which ordered above 2 K showed a metamagnetic transition at 2 K for fields below 70 kOe. The calculated effective moments per rare earth atom are close to the expected free ion values of R^3+ except for Sm which displays anomalous behavior in the paramagnetic state. The non-magnetic members of this series (Y, Lu) are characterized by an unusually large electronic specific heat coefficient (gamma ~ 60 mJ/mol K^2) and temperature-independent susceptibility term (chi_0 ~ 0.003 emu/mol), indicative of a relatively large density of states at the Fermi surface.