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Recent observations of quantum critical excitations (QCE) in columbite systems such as NiNb₂O₆ and CoNb₂O₆ have brought great attention to the field of Quantum Materials so that QCE can be realized for T > 0 K. [1,2]. Here we present detailed studies of magnetic field induced transitions in NiNb₂O₆ mapped on the field-temperature (H-T) phase diagram. The crystal structure analysis of the prepared sample of NiNb₂O₆ using X-ray diffraction and Rietveld refinement reveals orthorhombic crystal structure of space group is Pbcn (D_2h¹⁴) with lattice parameters a = 14.038(3) Å, b = 5.684(3) Å and c = 5.025(3) Å. The unit cell essentially consists of layers of Ni–Nb–Nb–Ni–Nb–Nb–Ni with slightly distorted hexagonal-closed-packed oxygen octahedra perpendicular to the a-axis. Low-temperature magnetic susceptibility (χ-T) measurements reveal antiferromagnetic (AFM) behavior below the Néel temperature T_N ~ 5.8 K along with two field induced transitions at H_C1 ~ 9.7 kOe and H_C2 ~ 27.8 kOe. The best fits of χ vs. T data for T > 40 K to modified Curie-Weiss law χ = χ₀ + C/(T-θ) with χ₀ = -2.3 × 10^-4 emu mol^-1 Oe^-1 yield θ = +11 K, and C = 1.36 emu K mol^-1 Oe^-1, the latter yielding the effective magnetic moment µ = 3.3 µ_B /Ni²⁺ ion confirming the effective spin S = 1 and g = 2.3, and the principal exchange interaction J₀ being ferromagnetic as in CoNb₂O₆ [3]. The H-T phase diagram mapped using the M-H isotherms and χ -T data at different fields will be discussed along with the intra-chain (J₀) and inter-chain (J₁ and J₂) exchange interactions determined from H_C1 and H_C2.

References:

[1] Y. Xu, et al. Phys. Rev. X 12, 021020 (2022)

[2] T. Liang et al.  Nat. Commun. 6, 7611 (2015)

[3] S. Thota et al., Phys. Rev. B 103, 064415 (2021)