Quasi-two-dimensional magnetism in Ru and Rh metal layers sandwiched between graphene sheets

Abstract

$4d$ transition-metal- [(TM)= Ru and Rh] metal-graphite (MG) has a unique layered structure, where the TM monolayer is sandwiched between adjacent graphene sheets. The magnetic properties of TM-MG based on natural graphite are investigated using dc and ac magnetic susceptibility. (i) Ru-MG magnetically behaves like a quasi-two-dimensional ferromagnet. This compound undergoes successive magnetic phase transitions at ${T}_{\mathrm{cu}}$ $(=16.3\ifmmode\pm\else\textpm\fi{}0.2\mathrm{K})$ and ${T}_{\mathrm{cl}}$ $(=12.8\ifmmode\pm\else\textpm\fi{}0.3\mathrm{K}).$ The origin of two phase transitions in Ru-MG is similar to that in stage-2 ${\mathrm{CoCl}}_{2}$ graphite intercalation compound ${(T}_{\mathrm{cu}}=8.9\mathrm{K}$ and ${T}_{\mathrm{cl}}=6.9--7.1\mathrm{K}),$ where the ferromagnetic layers are antiferromagnetically stacked along the c axis. The low-temperature phase below ${T}_{\mathrm{cl}}$ may be a reentrant spin-glass-like phase where the antiferromagnetic phase and spin-glass phase coexist. (ii) Rh-MG exhibits a superparamagnetic behavior. A ferromagnetic blocked state is formed below 9.7 K. The zero-field-cooled susceptibility shows a broad peak around 9.7 K. The irreversible effect of magnetization is observed below 13.5 K. The relaxation time obeys the Arrhenius law for thermal activation.