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Maruthi, R., Mohindar S. Seehra, Sayandeep Ghosh, Rohit Medwal, Rawat, R. S., Weise, B., Choi, E. S., & Subhash Thota. (2022). Determination of the tricritical point, H-T phase diagram and exchange interactions in the antiferromagnet MnTa2O6. Journal of Physics: Condensed Matter, 34(15), Article 155801. https://doi.org/10.1088/1361-648x/ac4cec
Journal of Physics: Condensed Matter
Using the analysis of the temperature and magnetic field dependence of the magnetization (M) measured in the temperature range of 1.5 K to 400 K in magnetic fields up to 250 kOe, the magnetic field-temperature (H–T) phase diagram, tricritical point and exchange constants of the antiferromagnetic MnTa2O6 are determined in this work. X-ray diffraction/Rietveld refinement and x-ray photoelectron spectroscopy of the polycrystalline MnTa2O6 sample verified its phase purity. Temperature dependence of the magnetic susceptibility χ (=M/H) yields the Néel temperature TN = 5.97 K determined from the peak in the computed ∂(χT)/∂T vs T plot, in agreement with the TN = 6.00 K determined from the peak in the CP vs T data. The experimental data of CP vs T near TN is fitted to CP = A|T − TN|−α yielding the critical exponent α = 0.10(0.13) for T > TN (T < TN). The χ vs T data for T > 25 K fits well with the modified Curie–Weiss law: χ = χ0 + C/(T − θ) with χ0 = −2.12 × 10−4 emu mol−1 Oe−1 yielding θ = −24 K, and C = 4.44 emu K mol−1 Oe−1, the later giving magnetic moment μ = 5.96 μB per Mn2+ ion. This yields the effective spin S = 5/2 and g = 2.015 for Mn2+, in agreement with g = 2.0155 measured using electron spin resonance spectroscopy. Using the magnitudes of θ and TN and molecular field theory, the antiferromagnetic exchange constants J0/kB = −1.5 ± 0.2 K and J⊥/kB = −0.85 ± 0.05 K for Mn2+ ions along the chain c-axis and perpendicular to the c-axis respectively are determined. The χ vs T data when compared to the prediction of a Heisenberg linear chain model provides semiquantitative agreement with the observed variation. The H–T phase diagram is mapped using the M–H isotherms and M–T data at different H yielding the tricritical point TTP (H, T) = (17.0 kOe, 5.69 K) separating the paramagnetic, antiferromagnetic, and spin-flop phases. At 1.5 K, the experimental magnitudes of the exchange field HE = 206.4 kOe and spin-flop field HSF = 23.5 kOe yield the anisotropy field HA = 1.34 kOe. These results for MnTa2O6 are compared with those reported recently in the isostructural MnNb2O6.
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