Composition dependence of magnetic order and spin chirality of Kagom\'{e} lattices in BaMn$_{\mathrm{1+x}}$Ru$_{\mathrm{5-x}}$O$_{11}$ R-type ferrites

The effects of atomic disorder on magnetic frustration have not been extensively studied. Single-crystal BaMn$_{2.49}$Ru$_{3.51}$O$_{11}$ exhibits three closely-spaced anomalies in the magnetization at temperatures T$_{1} =$ 183 K, T$_{2} =$ 171 K and T$_{3}$ $=$ 128 K, signaling complex magnetic/chiral ordering, due to an interplay between antiferromagnetic correlations, magnetic frustration and non-zero scalar chirality (induced by spin canting) within the hexagonal (Kagom\'{e}) ab-plane [1]. We observe that small increases in Ru content change the temperature and nature of the anomalies: A single crystal of composition BaMn$_{1.915}$Ru$_{4.085}$O$_{11}$ exhibits anomalies shifted to lower temperatures T$_{1} =$ 149 K, T$_{2} =$ 90 K and T$_{3} =$ 48 K. The anomaly at T$_{3}$ is rapidly weakened by fields H \textgreater 25 Oe applied parallel to the Kagom\'{e} plane for both compositions studied; whereas further field increases shift the onset of magnetic order substantially upward to T$_{1} =$ 175 K for the higher Ru concentration. \\[4pt] [1] L. Shlyk et al., Phys. Rev. B 81, 014413 (2010).