Magnetic order and lattice anomalies in theJ1−J2model systemVOMo

Abstract

High-resolution x-ray and neutron powder-diffraction measurements were performed on polycrystalline VOMoO 4 . Below Ӎ40 K the system orders in a simple Néel antiferromagnetic state ͑propagation vector k ជ =0͒, indicating a dominant role of the nearest-neighbor interactions. The order is three dimensional but the reduced saturated magnetic moment m of 0.41 ͑1͒ B / V 4+ at 2 K indicates strongly two-dimensional character and enhanced quantum fluctuations. On cooling, there is no evidence of a reduction of the crystal symmetry. However, neutron diffraction indicates an anomalous evolution of the lattice parameters, which can be related to the onset of magnetic correlations.Frustrated magnets based on transition metals have become subjects of many theoretical and experimental studies in the past years: 1,2 a variety of exotic quantum effects are expected when competitive interactions lead a system into a frustrated state, where it is impossible to satisfy all the pair interactions simultaneously. One of the most studied model systems is the spin-1 / 2 Heisenberg antiferromagnet on a square lattice with competing nearest-͑J 1 ͒ and next-nearest-͑J 2 ͒ neighbor antiferromagnetic interactions. In two dimensions, the zero-point quantum fluctuations ͑enhanced by a low spin value͒, combined with the frustration, are strong enough to destroy the long range ordering in the system even at zero temperature. The two limiting cases of this model are relatively simple and well understood: when J 1 ӷ J 2 , the system orders into a simple Néel state, whereas when J 1 Ӷ J 2 the problem can be treated in terms of two decoupled interpenetrating Néel lattices. In the mean-field limit, all the relative orientations of these two sublattices have the same energy, but the order-by-disorder mechanism 3 lowers the energy of the collinear states. The intermediate situation is still a matter of debate; in particular, different predictions exist concerning the magnetic and nonmagnetic ground states in the vicinity of the fully frustrated point ͑J 1 Ӎ 2 ϫ J 2 ͒ ͑Ref. 4͒.Recently, several new vanadium-based compounds have provided experimental realizations of the J 1 -J 2 model, and are currently receiving significant attention by the scientific community. The first widely studied prototype of this family was Li 2 VOSiO 4 ͑Ref. 5͒. At low temperature, this material was found to order in the collinear magnetic state. 6-8 The staggered magnetization from neutron scattering was found to be 0.63 B , in excellent agreement with J 2 / J 1 Ӎ 12, as obtained from band-structure calculations and bulk properties measurements. 9 Another window into this phase diagram is provided by the closely related system VOMoO 4 ͑Ref. 10͒. Initially, VOMoO 4 was considered as a weak one-dimensional antiferromagnet. 11-13 However, recent band-structure calculations by Carretta et al. 14 have shown that this system is essentially two dimensional ͑2D͒, with extremely weak interplanar coupling. The crystal structure of VOMoO 4 , shown in Fig. 1, presents many similarities w...

Magnetic correlation in the square-lattice spin system (CuBr)Sr2Nb3O10: A neutron diffraction study

“…16 Extensive experimental investigations, carried out on a number of vanadium-based square-lattice compounds Li 2 VOSiO 4 and Li 2 VOGeO 4 , reveal AFM J 1 and J 2 . 20 The AFM J 1 and J 2 have also been found for other systems, such as the two-dimensional (2D) square-lattice antiferromagnet Cu(pz) 2 (ClO 4 ) 2 (where pz denotes pyrazine), 21 VOMoO4, 22 and the layered perovskite PbVO 3 . 23,24 The square-lattice layered vanadium phosphate AA VO(PO 4 ) 2 with AA = Zn 2 also reveals AFM J 1 and J 2 .…”

Extension of the spin-12frustrated square lattice model: The case of layered vanadium phosphates

“…22, 23 The region of ferromagnetic (FM) J 1 -AFM J 2 was accessed by studying the layered vanadium phosphate Pb 2 VO(PO 4 ) 2 (Refs. 24,25,26) and the related AA VO(PO 4 ) 2 compounds with AA = SrZn and BaZn.…”

Massively parallel simulations of strong electronic correlations: Realistic Coulomb vertex and multiplet effects

“…Later-on, a high-temperature expansion study of the J 1 -J 2 Heisenberg model pointed out that the experimental specific heat and susceptibility of Li 2 VOSiO 4 from references [62,63] could be also compatible with large J 2 /J 1 values obtained in DFT calculations [68]. More recently, neutron diffraction and resonant X-ray scattering experiments have reported magnetic order in three dimensions for both systems [69,70]. These theoretical and experimental results, taken together, suggest a weak frustration scenario.…”

“…Our calculations [25] support a weak frustration picture for both vanadates, with a small but non-negligible degree of three-dimensionality, which fully account for the three-dimensional magnetic order reported in experiments. Although weak, the frustration is large enough to explain the partial reduction of the ordered magnetic moments measured via neutron scattering experiments [69,70].…”