Robust spin liquid state against magnetic-dilution in the bi-layer Kagome material Ca${}_{10}$Cr${}_7$O${}_{28}$

Abstract

Recently, the bi-layer Kagome lattice material Ca${}_{10}$Cr${}_7$O${}_{28}$ has been shown to be a quasi-two-dimensional quantum spin liquid (QSL) where the frustration arises from a balance between competing ferromagnetic and antiferromagnetic exchange within a bi-layer. In an attempt to understand what happens when this balance is disturbed, we present a magnetic dilution study. Specifically, we have synthesized Ca${}_{10}$(Cr${}_{1-x}$V${}_x$)${}_7$O${}_{28}$ (0 $\le$ x $\le$ 0.5) where magnetic Cr${}^{5+}$ ($S=1/2$) is partially replaced by non-magnetic V${}^{5+}$ ($S=0$). We also synthesized the fully non-magnetic isostructural material Ca${}_{10}$V${}_7$O${}_{27.5}$. We report a detailed structural, magnetic and heat capacity study on these materials. A monotonic increase in the unit cell parameters is found for the Ca${}_{10}$(Cr${}_{1-x}$V${}_x$)${}_7$O${}_{28}$ materials with increasing $x$. An order of magnitude decrease in the Curie-Weiss temperature from $4$ to $0.5$~ K is found for the partial V substituted samples, which indicates a relative increase in antiferromagnetic exchange with increase in V content. However, despite this change in the relative balance in the exchange interactions and the large disorder introduced, no magnetic ordering or spin-glass state is observed down to $2$~K in the V substituted samples. The QSL state of the parent compound thus seems surprisingly robust against these large perturbations.

6 figures, 2 Tables