Thermodynamic Properties, Mössbauer Study, and First-Principles Calculations of TlFe(MoO4)2 C

We report the results of magnetization and specific heat measurements, a ⁵⁷Fe Mossbauer study of hyperfine interactions and density functional theory calculations in TlFe(MoO₄)₂ demonstrating two magnetic phase transitions at TN₂ = 5.7 K and TN₁ = 6.2 K. In the asymptotical critical region TN₂ ≤ T ≤ TN₁, the temperature dependence of the average hyperfine magnetic field ⟨Bₕf(T)⟩ at the ⁵⁷Fe nuclei is well-described by the power law ⟨Bₕf(T)⟩ ∝ tᵝ with the static critical exponent β ≈ 0.37 inherent for a three-dimensional magnet. In this range, the Mossbauer spectra are described in terms of collinear spin-density-wave with the inclusion of high-order harmonics. The spectra of the low-temperature phase, below TN₂, are well-fitted by a single six-line Zeeman pattern reflecting the equivalence of magnetic sites occupied by Fe³⁺ ions in an antiferromagnetic structure. The first-principles calculations allowed estimation of the strength of main exchange interactions.