Thermodynamic and transport properties of single crystalline RCo$_{2}$Ge$_{2}$ (R = Y, La-Nd, Sm-Tm)

Tai Kong; Charles E. Cunningham; Valentin Taufour; Sergey L. Bud'ko; Malinda L. C. Buffon; Xiao Lin; Heather Emmons; Paul C. Canfield

doi:10.1016/j.jmmm.2014.01.072

paper

Thermodynamic and transport properties of single crystalline RCo $_{2}$ Ge $_{2}$ (R = Y, La-Nd, Sm-Tm)

arXiv:1311.3321 · doi:10.1016/j.jmmm.2014.01.072

Abstract

Single crystals of RCo $_{2}$ Ge $_{2}$ (R = Y, La-Nd, Sm-Tm) were grown using a self-flux method and were characterized by room-temperature powder x-ray diffraction; anisotropic, temperature and field dependent magnetization; temperature and field dependent, in-plane resistivity; and specific heat measurements. In this series, the majority of the moment-bearing members order antiferromagnetically; YCo $_{2}$ Ge $_{2}$ and LaCo $_{2}$ Ge $_{2}$ are non-moment-bearing. Ce is trivalent in CeCo $_{2}$ Ge $_{2}$ at high temperatures, and exhibits an enhanced electronic specific heat coefficient due to Kondo effect at low temperatures. In addition, CeCo $_{2}$ Ge $_{2}$ shows two low-temperature anomalies in temperature-dependent magnetization and specific heat measurements. Three members (R = Tb-Ho) have multiple phase transitions above 1.8 K. Eu appears to be divalent with total angular momentum L = 0. Both EuCo $_{2}$ Ge $_{2}$ and GdCo $_{2}$ Ge $_{2}$ manifest essentially isotropic paramagnetic properties consistent with J = S = 7/2. Clear magnetic anisotropy for rare-earth members with finite L was observed, with ErCo $_{2}$ Ge $_{2}$ and TmCo $_{2}$ Ge $_{2}$ manifesting planar anisotropy and the rest members manifesting axial anisotropy. The experimentally estimated crystal electric field (CEF) parameters B $_{2}^{0}$ were calculated from the anisotropic paramagnetic $I^¸_{ab}$ and $I^¸_{c}$ values and follow a trend that agrees well with theoretical predictions. The ordering temperatures, T $_{N}$ , as well as the polycrystalline averaged paramagnetic Curie-Weiss temperature, $I^_{a v g}$ , for the heavy rare-earth members deviate from the de Gennes scaling, as the magnitude of both are the highest for Tb, which is sometimes seen for extremely axial systems. Except for SmCo $_{2}$ Ge $_{2}$ , metamagnetic transitions were observed at 1.8 K for all members that ordered antiferromagnetically.

26 pages, 16 figures

Thermodynamic and transport properties of single crystalline RCo2​Ge2​ (R = Y, La-Nd, Sm-Tm)

Abstract

Thermodynamic and transport properties of single crystalline RCo $_{2}$ Ge $_{2}$ (R = Y, La-Nd, Sm-Tm)