Effect of doping in BaNi 2 V 2 O 8 , a two-dimensional honeycomb antiferromagnet R. Nath, J. Das, A.V. Mahajan à Department of Physics, Indian Institute of Technology, Bombay, Mumbai-400076, India Abstract We report the temperature dependence of susceptibility wðT Þ of the two-dimensional (2D) honeycomb antiferromagnetic (AF) BaðNi 1x Cu x Þ 2 V 2 O 8 for x ¼ 0:0; 0:05 and 0.1. The undoped BaNi 2 V 2 O 8 is known to exhibit long-range-order (LRO) below T N 50 K with J =k B ¼ 48 K. We find that doping Cu (S ¼ 1=2) at Ni (S ¼ 1) site results in a magnetic dilution effect which suppresses the three-dimensional (3D) ordering temperature (T N ). Our results are compared with those of nonmagnetic Mg-doped BaNi 2 V 2 O 8 . PACS: 75.40.Cx Keywords: 2D XY antiferromagnet; Dilution effect 1. Introduction There is currently an enormous interest in quasi- one-dimensional (1D) and quasi-two-dimensional (2D) magnetic systems due to a host of exotic features that they exhibit. For instance, S ¼ 1 2 and S ¼ 1 antiferromagnetic (AF) chains have novel ground states such as Spin-Peierls [1] and Haldane gap [2] states. On the other hand 2D AF systems are interesting due to their intimate connection with parent compounds of high-T c cuprate super- conductors [3] and various ground state properties such as spin-flop [4] and Kosterlitz–Thouless transitions [5]. A study of impurity induced effects in such systems constitutes a powerful probe of the ground state and the excitations from the ground state. So far not many compounds have been reported where the dilution effect has been extensively studied [6–8]. BaNi 2 V 2 O 8 is an S ¼ 1 2D AF system belonging to the space group R-3 with lattice constants a ¼ 5:0375 ( A and c ¼ 22:33 ( A [9]. This compound is known as a 2D XY model system. It consists of honeycomb layers of edge-sharing NiO 6 octahe- dra. These magnetic V 4þ O 4 layers are separated by ARTICLE IN PRESS