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Magnetic field-temperature phase diagram, exchange constants andspecific heat exponents of the antiferromagnet MnNb₂O₆
Citation
Maruthi, R., Ghosh, S., Seehra, M. S., Joshi, D. C., Chowdhury, M. R., Medwal, R., Rawat, R. S., Weise, B., & Thota, S. (2021). Magnetic field-temperature phase diagram, exchange constants andspecific heat exponents of the antiferromagnet MnNb2O6. Journal of Physics: Condensed Matter, 33(34), Article 345801. https://doi.org/10.1088/1361-648X/ac0936
Author
Maruthi, R.
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Ghosh, Sayandeep
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Seehra, Mohindar Singh
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Joshi, Deep C.
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Chowdhury, Mouli Roy
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Medwal, Rohit
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•
Weise, Bruno
•
Thota, Subhash
Abstract
This work presents the magnetic field-temperature (H–T) phase diagram, exchange constants, specific heat (CP) exponents and magnetic ground state of the antiferromagnetic MnNb2O6 polycrystals. Temperature dependence of the magnetic susceptibility χ (=M/H) yields the Néel temperature TN = 4.33 K determined from the peak in the computed ∂(χT)/∂T vs T plot in agreement with the transition in the CP vs T data at TN = 4.36 K. The experimental data of CP vs T near TN is fitted to CP = A|T − TN|−α yielding the critical exponent α = 0.12 (0.15) for T > TN (T < TN). The best fit of χ vs T data for T > 50 K to χ = χ0 + C/(T − θ) with χ0 = −1.85 × 10−4 emu mol−1 Oe−1 yields θ = −17 K, and C = 4.385 emu K mol−1 Oe−1, the latter giving magnetic moment μ = 5.920μB per Mn2+ ion. This confirms the effective spin S = 5/2 and g = 2.001 for Mn2+ and the dominant exchange interaction being antiferromagnetic in nature. Using the magnitudes of θ and TN and molecular field theory (MFT), the exchange constants J0/kB = −1.08 K for Mn2+ ions along the chain c-axis and J⊥/kB = −0.61 K as the interchain coupling perpendicular to c-axis are determined. These exchange constants are consistent with the expected χ vs T variation for the Heisenberg linear chain. The H–T phase diagram, mapped using the M–H isotherms and M–T data at different H combined with the reported data of Nielsen et al, yields a triple-point TTP (H, T) = (18 kOe, 4.06 K). The spin–flopped state above TTP and the forced ferromagnetism for H > 192 kOe are used to estimate the anisotropy energy HA ≈ 0.8 kOe.
Date Issued
2021
Publisher
IOP Publishing
Journal
Journal of Physics: Condensed Matter