Magnetic properties of $R$Rh$_6$Ge$_4$ ($R$ = Pr, Nd, Sm, Gd-Er) single crystals

TL;DR

This study synthesizes and characterizes single crystals of $R$Rh$_6$Ge$_4$ ($R$ = Pr, Nd, Sm, Gd-Er), revealing diverse magnetic behaviors including ferromagnetism, antiferromagnetism, and ferrimagnetism, influenced by crystal electric field effects.

Contribution

First comprehensive synthesis and magnetic characterization of $R$Rh$_6$Ge$_4$ single crystals across multiple rare-earth elements, highlighting their complex magnetic properties and anisotropies.

Findings

NdRh$_6$Ge$_4$ and SmRh$_6$Ge$_4$ are ferromagnetic.

GdRh$_6$Ge$_4$ and DyRh$_6$Ge$_4$ exhibit antiferromagnetic transitions.

DyRh$_6$Ge$_4$ shows multiple magnetic transitions and plateaus.

Abstract

Single crystals of $R$Rh$_6$Ge$_4$ ($R$ = Pr, Nd, Sm, Gd - Er) were synthesized using a Bi flux and their physical properties were characterized by magnetization, resistivity, and specific heat measurements. These compounds crystallize in the noncentrosymmetric LiCo$_6$P$_4$-type structure (space group $P\bar{6}m2$), where rare-earth atoms form a triangular lattice in the $ab$-plane and chains along the $c$-axis. PrRh$_6$Ge$_4$ and ErRh$_6$Ge$_4$ do not exhibit magnetic transitions above 0.4 K. NdRh$_6$Ge$_4$ and SmRh$_6$Ge$_4$ are ferromagnets, while GdRh$_6$Ge$_4$ and DyRh$_6$Ge$_4$ show antiferromagnetic transitions, \red{whereas HoRh$_6$Ge$_4$ is a ferrimagnet}. In addition, DyRh$_6$Ge$_4$ shows multiple transitions and magnetization plateaus when a magnetic field is applied along the $c$-axis. In SmRh$_6$Ge$_4$, like the Ce counterpart, the crystalline-electric field (CEF) effect leads to an easy plane anisotropy, while in other compounds it gives rise to a pronounced uniaxial anisotropy.