Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in Rb${}_2$Cu${}_2$Mo${}_3$O${}_{12}$

Abstract

We have investigated magnetic properties of Rb${}_2$Cu${}_2$Mo${}_3$O${}_{12}$ powder. Temperature dependence of magnetic susceptibility and magnetic-field dependence of magnetization have shown that this cuprate is a model compound of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor (2NN) competing interactions (competing system). Values of the 1NN and 2NN interactions are estimated as $J_1=-138$ K and $J_2=51$ K ($\alpha \equiv J_2/J_1=-0.37$). This value of $\alpha$ suggests that the ground state is a spin-singlet incommensurate state. In spite of relatively large $J_1$ and $J_2$, no magnetic phase transition appears down to 2 K, while an antiferromagnetic transition occurs in other model compounds of the competing system with ferromagnetic 1NN interaction. For that reason, Rb${}_2$Cu${}_2$Mo${}_3$O${}_{12}$ is an ideal model compound to study properties of the incommensurate ground state that are unconfirmed experimentally.

6 pages, 4 figures