Phase diagram of the frustrated spatially-anisotropicS=1antiferromagnet on a square lattice

Abstract

We study the S = 1 square lattice Heisenberg antiferromagnet with spatially anisotropic nearest-neighbor couplings J 1x and J 1y frustrated by a next-nearest-neighbor coupling J 2 numerically using the density-matrix renormalization-group ͑DMRG͒ method and analytically employing the Schwinger-Boson mean-field theory ͑SBMFT͒. Up to relatively strong values of the anisotropy, within both methods we find quantum fluctuations to stabilize the Néel-ordered state above the classically stable region. Whereas SBMFT suggests a fluctuationinduced first-order transition between the Néel state and a stripe antiferromagnet for 1 / 3 Յ J 1x / J 1y Յ 1 and an intermediate paramagnetic region opening only for very strong anisotropy, the DMRG results clearly demonstrate that the two magnetically ordered phases are separated by a quantum-disordered region for all values of the anisotropy with the remarkable implication that the quantum paramagnetic phase of the spatially isotropic J 1 -J 2 model is continuously connected to the limit of decoupled Haldane spin chains. Our findings indicate that for S = 1 quantum fluctuations in strongly frustrated antiferromagnets are crucial and not correctly treated on the semiclassical level.

Existence of featureless paramagnets on the square and the honeycomb lattices in 2+1 dimensions

“…In the end, we will comment on the connection to previous studies Ref. 27,28 on the spin-1 square lattice. From a field theory point of view, to obtain a paramagnetic phase, one can start from an classically ordered background and disorder it through the proliferation of topological defects/excitations or instantons.…”

Ba4[Mn3N6], a Quasi-One-Dimensional Mixed-Valent Nitridomanganate (II, IV)

“…LSDA calculations are known to underestimate magnetic moments in strongly correlated semiconductors. It is also well known that experimentally determined ordered magnetic moments in highly frustrated systems are often reduced in comparison with spin-only values, typically, as a consequence of quantum fluctuations [46]. Therefore, more experimental data would be necessary to probe the importance of on-site correlations in Ba 4 [Mn 3 N 6 ].…”

Orbital ordering and unfrustrated(π,0)magnetism from degenerate double exchange in the iron pnictides

“…By contrast, the local-density approximation seems to be adequate 30 to describe their band structure. As a result of this dichotomy, both itinerant-magnetism [30][31][32][33][34][35][36][37][38] and local-moment [27][28][29][39][40][41][42][43][44] scenarios have been suggested to explain the unusual stripe antiferromagnetism. Although the former weak-coupling theories which attribute the magnetism to a spin-density-wave instability of a nested Fermi surface, can explain the magnetic low-energy excitations around the correct ordering wave vector, they fail to describe the spectra at higher energies which have been measured in great detail by inelastic neutron scattering.…”