A microscopic model for a class of mixed-spin quantum antiferromagnets

We propose a microscopic model that describes the magnetic behavior of the mixed-spin quantum systems R$_2$BaNiO$_5$ (R= magnetic rare earth). An evaluation of the properties of this model by Quantum Monte Carlo simulations shows remarkable good agreement with the experimental data and provides new insight into the physics of mixed-spin quantum magnets.Comment: revised version to be published in Phys. Rev.

Effects of substituting rare-earth ion R by non-magnetic impurities in R2BaNiO5R_2BaNiO_5 - theory and numerical DMRG results

In this paper we study the effect of substituting R (rare-earth ion) by non-magnetic ions in the spin-1 chain material $R_2BaNiO_5$. Using a strong-coupling expansion and numerical density matrix renormalization group calculations, we show that spin-wave bound states are formed at the impurity site. Experimental consequences of the bound states are pointed out.Comment: 5 pages, 4 postscript figure