Mohammad Siahatgar

Frustrated local-moment models for iron pnictide magnetism

The low-energy spin excitations of the Fe pnictide parent compounds have been determined by inelastic neutron scattering and interpreted within the local moment

Ordered moment in the anisotropic and frustrated square lattice Heisenberg model

{J}_{1a,b}\text{\ensuremath{-}}{J}_{2}

Moment screening in the correlated Kondo lattice model

Heisenberg model with orthorhombic symmetry. This has led to alternative exchange models that strongly differ in the size of anisotropy. Although the compounds are itinerant the localized spin model can explain basic features of the excitations. The inherent frustration of this model leads to quantum fluctuations and possible moment reduction. We investigate this question in detail using spin-wave approximation and partly exact diagonalization Lanczos calculations for finite clusters. We find that the orthorhombic anisotropy stabilizes the columnar antiferromagnetic phase and its moment. For the exchange models proposed from inelastic neutron scattering we can exclude a strong influence of frustration on the moment size. We also investigate dependence of magnetization and susceptibility on field and temperature.

The two-dimensional frustrated Heisenberg model on the orthorhombic lattice

The two-dimensional frustrated next-to-nearest-neighbor Heisenberg model on the square lattice is a prime example for a spin system where quantum fluctuations can either destroy or stabilize magnetic order. The phase boundaries and staggered moment dependence on the frustration ratio

Staggered-moment dependence on field-tuned quantum fluctuations in two-dimensional frustrated antiferromagnets

{J}_{2}/{J}_{1}

Stabilization of Néel order in frustrated magnets with increasing magnetic field

of the exchange constants are fairly well understood both from approximate analytical and numerical methods. In this work we use exact diagonalization for finite clusters for an extensive investigation of the more general

Quantum Effects in Uniform and Staggered Moment of Frustrated Quasi-2D Antiferromagnets

{J}_{1a,b}

Magnetic moment screening in the correlated Kondo lattice model

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Field-induced staggered moment stabilization in frustrated quantum magnets

{J}_{2}

Non-monotonic magnetic field dependence of the staggered-moment in two-dimensional frustrated antiferromagnets

model which includes a spatial exchange anisotropy between next-neighbor spins. We introduce a systematic way of tiling the square lattice and, for this low symmetry model, define a controlled procedure for the finite size scaling that is compatible with the possible magnetic phases. We obtain ground-state energies, structure factors, and ordered moments and compare with the results of spin-wave calculations. We conclude that