Magnetic properties of Rb2Cu2Mo3O12 including a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor exchange interactions -: art. no. 104426

We have investigated magnetic properties of Rb2Cu2Mo3O12 powder. Temperature dependence of magnetic susceptibility and magnetic-field dependence of magnetization have shown that this cuprate can be considered as a 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 exchange interactions are estimated as J(1)=-138 K and J(2)=51 K (alphaequivalent toJ(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, Rb2Cu2Mo3O12 is a suitable compound to study properties of the incommensurate ground state that are unconfirmed experimentally.