Direct observations of ordered R2CuSi3 (R=Ce and Nd) cluster-glass compounds in real space by HRTEM

We present the direct observations of microstructure with clustering by electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM) on cluster-glass (CG) magnetic compounds R2CuSi3 (R=Ce and Nd) related to a hexagonal AlB2-type structure. Observed diffraction patterns show superstructure reflections at 121212-typed positions, which are very similar to the results observed for the CG compound U2IrSi3. Fourier-filtered HRTEM images clearly exhibit a domain structure. The size of the domains with a base-centered ordering structure in Ce2CuSi3 is estimated to be 2-3 nm in much smaller than that in Nd2 CuSi3. These observations are consistent with the inferences based on the magnetic measurements, and can be considered as the direct evidence for the formation of magnetic cluster in Ce2CuSi3 and Nd2CuSi3.