Magnetic exchange interactions and non-Debye relaxation in spin-3/2 frustrated Kagomé magnet Co₃V₂O₈

Abstract

We report the experimental determination of the magnetic exchange parameter (J/kB = 2.88 ± 0.02 K) for the Spin-3/2 ferromagnetic (FM) Kagomé lattice system: Co3V2O8 using the temperature dependence of dc-magnetic susceptibility χ(T) data by employing the fundamental Heisenberg linear chain model. Our results are quite consistent with the theoretically reported nearest neighbor dominant FM exchange coupling strength Jex-NN ∽ 2.45 K. Five different magnetic phase transitions (6.2-11.2 K) and the spin-flip transition (9.6-7.7 kOe) have been probed using the ∂(χT)/∂T vs. T, heat capacity (CP-T) and differential isothermal magnetization curves. Among such sequence of transitions, the prominent ones being incommensurate antiferromagnetic (AFM) state at 11.2K, commensurate AFM state at 8.8 K, and commensurate FM state across 6.9 K. All the successive magnetic phase transitions have been mapped onto a single H-T plane through which one can easily distinguish the above-mentioned different phases. The magnetic contribution of the CP-T near TN has been analyzed using the power-law expression CM = A|T − TN|−α resulting in the critical exponent α = 0.18 ± 0.01 (0.15 ± 0.003) for T < TN (T > TN), respectively for the Co3V2O8. It is interesting to note that non-Debye type dipole relaxation is quite prominent in Co3V2O8 and was evident from the Kohlrausch-Williams-Watts analysis of complex modulus and impedance spectra (0≤β≤1). Mott’s variable-range hopping of charge carriers process is evident through the resistivity analysis (ρac‒T −1/4) in the temperature range 275−350°C. Moreover, the frequency-dependent analysis of σac(ω) follows Jonscher's power law yielding two distinct activation energies (Ea~0.37 and 2.29 eV) between the temperature range 39 − 99°C and 240 − 321°C.