Magnetic exchange interactions and non-Debye relaxation in Spin-3/2 Frustrated Kagomé Magnet Co 3 V 2 O 8 .

We report the experimental determination of the magnetic exchange parameter ( J / k B = 2.88 ± 0.02 K) for the Spin-3/2 ferromagnetic (FM) Kagomé lattice system: Co 3 V 2 O 8 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 J ex-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 (C P -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 C P -T near T N has been analyzed using the power-law expression C M = A|T - TN| -α resulting in the critical exponent α = 0.18 ± 0.01 (0.15 ± 0.003) for T < T N (T > T N ), respectively for the Co 3 V 2 O 8 . It is interesting to note that non-Debye type dipole relaxation is quite prominent in Co 3 V 2 O 8 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 (ρ ac ‒T -1/4 ) in the temperature range 275-350°C. Moreover, the frequency-dependent analysis of σ ac (ω) follows Jonscher's power law yielding two distinct activation energies (E a ~0.37 and 2.29 eV) between the temperature range 39 - 99°C and 240 - 321°C.