Physical properties of the quasi-two-dimensional square lattice antiferromagnet Ba2FeSi2O7

We report magnetization (chi, M), magnetic specific heat (C-M), and neutron powder diffraction results on a quasi-two-dimensional (2D) S = 2 square lattice antiferromagnet Ba2FeSi2O7 consisting of FeO4 tetrahedrons with highly compressive tetragonal distortion (27%). Despite of the quasi-2D lattice structure, both chi and C-M present three-dimensional magnetic long-range ordering below the Neel temperature T-N = 5.2 K. Neutron diffraction data show a collinear Q(m) =(1,0,1/2) antiferromagnetic (AFM) structure below T-N but the ordered moment aligned in the ab plane is suppressed by 26% from the ionic spin S = 2 value (4 mu(B)). Both the AFM structure and the suppressed moments are well explained by using Monte Carlo simulations with a large single-ion in-plane anisotropy D = 1.4 meV and a rather small Heisenberg exchange J(intra) = 0.15 meV in the plane. The characteristic 2D spin fluctuations are recognized in the magnetic entropy release and diffuse scattering above T-N. This new quasi-2D magnetic system also displays unusual nonmonotonic dependence of T-N as a function of magnetic field H.

Automated summary

The study found that a quasi-two-dimensional square lattice antiferromagnet with highly compressive tetragonal distortion exhibits three-dimensional magnetic long-range ordering. Neutron diffraction data shows a collinear antiferromagnetic structure below the Neel temperature, but the aligned magnetic moment in the ab plane is suppressed, which can be well explained by Monte Carlo simulations.