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

Journal Article · 27 December 2021 · Physical Review B

DOI: https://doi.org/10.1103/physrevb.104.214434 · OSTI ID:1841485

Jang, Tae-Hwan  ^[1]; Do, Seung-Hwan  ^[2]; Lee, Minseong ^[3]; Wu, Hui  ^[4]; Brown, Craig M.  ^[4]; Christianson, Andrew D.  ^[5]; Cheong, Sang-Wook ^[6]; Park, Jae-Hoon  ^[1]

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1. Pohang Univ. of Science and Technology (POSTECH) (South Korea)
2. Pohang Univ. of Science and Technology (POSTECH) (South Korea); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab)
4. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research
5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
6. Pohang Univ. of Science and Technology (POSTECH) (South Korea); Pohang Univ. of Science and Technology (POSTECH) (South Korea). Lab. for Pohang Emergent Materials and Department of Physics; Rutgers Univ., Piscataway, NJ (United States). Rutgers Center for Emergent Materials

In this work, we report magnetization (χ, $M$), magnetic specific heat ( $C_{\mathrm{M}}$), and neutron powder diffraction results on a quasi-two-dimensional (2D) $S=2$ square lattice antiferromagnet ${\mathrm{Ba}}_2{\mathrm{FeSi}}_2{\mathrm{O}}_7$ consisting of ${\mathrm{FeO}}_4$ tetrahedrons with highly compressive tetragonal distortion (27%). Despite of the quasi-2D lattice structure, both χ and $C_{\mathrm{M}}$ present three-dimensional magnetic long-range ordering below the Néel temperature $T_{\mathrm{N}}=5.2\mathrm{K}$. Neutron diffraction data show a collinear ${\mathit{Q}}_{\mathit{m}}=$(1,0,1/2) antiferromagnetic (AFM) structure below $T_{\mathrm{N}}$ but the ordered moment aligned in the $ab$ plane is suppressed by 26% from the ionic spin $S=2$ value ( $4{\mu }_{\mathrm{B}}$). 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 $J_{\mathrm{intra}}=0$.15 meV in the plane. The characteristic 2D spin fluctuations are recognized in the magnetic entropy release and diffuse scattering above $T_{\mathrm{N}}$. This new quasi-2D magnetic system also displays unusual nonmonotonic dependence of $T_{\mathrm{N}}$ as a function of magnetic field $H$.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: POSTECH; USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-00OR22725; FG02-07ER46382
• OSTI ID: 1841485
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 21 Vol. 104; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English