On the Possibility of Ferromagnetism in Nanosized CuCl2

Copper chloride consists of parallel chains of CuCl2. The chains are sufficiently far apart such that the electronic and magnetic properties of CuCl2 have been approximated as arising from isolated chains. Density functional theory using the LANL2DZ/6-31G* basis set has been used to calculate the total energy of CuCl2 chains having nanometer length. The calculations, which are performed as a function of chain length, predict that chains having ferromagnetic order have a lower energy than chains with no order. Calculations of the band gap as a function of length for the ferromagnetic chains indicate that chains greater than 6？nm may be semiconducting suggesting that nanosized CuCl2 chains have the potential to be magnetic semiconductors. 1. Introduction There is much interest in the materials research community in magnetic nanoparticles because of present and potential applications, such as data storage and targeted delivery of drugs to diseased tissue. One of the most interesting results is the observation that bulk materials which are not ferromagnetic can become ferromagnetic on nanosizing. For example, rhodium is paramagnetic at all temperatures but has shown to be ferromagnetic when it has less than 30 atoms [1]. Materials such as CuO and NiO which are antiferromagnetic in the bulk become ferromagnetic when they are of nanometer dimensions [2, 3]. In this work theoretical methods are used to show that nanoparticles of copper chloride could be ferromagnetic. The unit cell of copper chloride is shown in Figure 1. The structure consists of parallel one dimensional chains of CuCl2. The distance between the chains is appreciably larger than the distance between the copper atoms within the chains so that the chains can be treated as noninteracting. Within the chains the copper atoms are linked together along the chain by bridging chlorine atoms from each copper. The exchange interaction is facilitated through these Cl atoms. The electronic and magnetic properties of the material can be approximated by treating isolated CuCl2 chains. There is experimental evidence for this conclusion. Bulk CuCl2 undergoes a paramagnetic to antiferromagnetic transition at 70？K. The temperature dependence of the measured susceptibility has been well accounted for by treating the chains as noninteracting using the Ising model of magnetism which has an exact solution in one dimension [4]. Figure 1: The unit cell of crystalline CuCl 2. In this work density functional theory (DFT) is used to calculate the total energy of the paramagnetic and ferromagnetic state of CuCl2 chains