Browsing by Author "Maruthi, R."
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- PublicationMetadata onlyDetermination of the tricritical point, H-T phase diagram and exchange interactions in the antiferromagnet MnTa2O6(2022)
;Maruthi, R. ;Seehra, Mohindar S. ;Ghosh, Sayandeep ;Medwal, Rohit; ;Weise, Bruno ;Choi, Eun SangThota, SubhashUsing 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.WOS© Citations 6 255 - PublicationOpen AccessMagnetic field-temperature phase diagram, exchange constants andspecific heat exponents of the antiferromagnet MnNb₂O₆(2021)
;Maruthi, R. ;Ghosh, Sayandeep ;Seehra, Mohindar Singh ;Joshi, Deep C. ;Chowdhury, Mouli Roy ;Medwal, Rohit; ;Weise, BrunoThota, SubhashThis 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.WOS© Citations 7 64 54 - PublicationOpen AccessMagnetic ground state and exchange interactions in the Ising chain ferromagnet CoNb2O6(2021)
;Thota, Subhash ;Ghosh, Sayandeep ;Maruthi, R. ;Joshi, Deep C. ;Medwal, Rohit; Seehra, Mohindar SinghReported here are measurements and analysis of the magnetization (M) versus temperature (1.9–400 K) in magnetic fields H up to 90 kOe for a polycrystalline sample of Ising chain ferromagnet Co Nb2 O6 with TC = 2.9K. For T > TC, the fit of magnetic susceptibility χ = M /H (H = 300 Oe) to χ = χ0 + C / (T−Θ) with χ0 = 0.0009 emu mol–1 Oe–1 determined from high -T data yields Θ = 11K and magnetic moment μ = 4.994μB per Co2+ ion calculated from experimental C = 3.12 emu K mol–1 Oe–1. Values of g obtained from μ2 / μB2 = g2S (S + 1) for spin S = 1/2 and 3/2 are used to determine μZ = g S μB and compared with μZ obtained from saturation magnetization and neutron diffraction for T ≪ TC. This analysis of the data for both above and below TC shows that the ground state of Co2+ in Co Nb2 O6 has the effective spin S = 1/2 and not S = 3/2 expected from Hund's rules, the S = 1/2 ground state resulting from the combined effects of a noncubic crystalline field and spin-orbit coupling. The fit of the data for T > TC to χ = χ0 + (C/T) exp (J0 / 2kBT) valid for an Ising chain with S = 1/2 yields the intrachain ferromagnetic exchange constant J0 / kB = 6.2K, whereas the g value with S = 1/2 and the experimental critical fields for spin flips yields interchain antiferromagnetic exchange constants J1 / kB = −0.42K and J2 / kB = − 0.67K.WOS© Citations 16Scopus© Citations 17 64 53