Magnetic ordering of the Mn sublattice: Dense Kondo-lattice behavior of Ce in(RPd3)8Mn(R=La,Ce)

Abstract

We have synthesized interstitial compounds $(R{\mathrm{Pd}}_{3}{)}_{8}\mathrm{Mn}$ $(R=\mathrm{La}$ and Ce). The Mn ions in these compounds, present in ``dilute'' concentrations of just 3 molar percent, form a regular sublattice with an unusually large Mn-Mn near-neighbor distance of $\ensuremath{\sim}8.5\mathrm{\AA{}}.$ While the existence of $(R{\mathrm{Pd}}_{3}{)}_{8}M$ $(M:$ p-block element) is already documented in the literature, the present work reports on the formation of this phase with M being a $3d$ element. In $({\mathrm{LaPd}}_{3}{)}_{8}\mathrm{Mn},$ the Mn sublattice orders antiferromagnetically, as inferred from the peaks in low-field magnetization at 48 and 23 K. The latter peak progressively shifts towards lower temperatures in increasing magnetic field and disappears below 1.8 K in a field of $\ensuremath{\sim}8\mathrm{kOe}.$ On the other hand, in $({\mathrm{CePd}}_{3}{)}_{8}\mathrm{Mn}$ the Mn sublattice undergoes a ferromagnetic transition around 35 K. The Ce ions form a dense Kondo lattice and are in a paramagnetic state at least down to 1.5 K. A strongly correlated electronic ground state, arising from the Kondo effect, is inferred from the large extrapolated value of $C/T=275\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{Ce}{\mathrm{K}}^{2}$ at $T=0\mathrm{K}.$