Magnetoelectric coupling in solid solution of Ni3-xCoxTeO6 (0 ≤ x ≤ 2.85)

Abstract

We systematically investigate the structural, magnetic, and dielectric properties of polycrystalline samples Ni_3-xCo_xTeO₆ (0 ≤ x ≤ 2.85). Powder X-ray diffraction reveals a structural transition from rhombohedral (R3) to monoclinic (C2/c) with increasing Co²⁺ substitution. The rhombohedral phase (R3) persists up to x  ≤ 1.5, while x  ∼ 2.55 and 2.85 adopt the monoclinic (C2/c) structure of Co₃TeO₆. Lattice parameters a and c increase linearly with Co²⁺ content, obeying Vegard’s law. The DC magnetic susceptibility, χ(T), study reveals long-range antiferromagnetic ordering at T_N ∼ 53 K and weak ferro/ferrimagnetic ordering at T_c ∼ 82 K for lower Co²⁺ substitution. As Co²⁺ content increases, T_N shifts to ∼49 K, and T_c disappears at the critical concentration. For x  ∼ 2.55, χ(T) reveals multiple magnetic transitions: short-range order at T_m ∼ 50 K, a cusp at T_N1 ∼ 32 K, T_N2 ∼ 28.3 K, and an abrupt change at 21.8 K. For higher substitution (x ∼ 2.85), these transitions shift slightly to lower temperatures, T_m ∼ 49.3 and T_N2 ∼ 26.2, resembling Co₃TeO₆ except for the presence of T_m. All the measured samples show dielectric peaks near magnetic transitions, suggesting a magneto-dielectric effect. Our results demonstrate that Co substitution in Ni₃TeO₆ tunes both magnetic and dielectric properties across the composition range. Notably, compositions such as NCTO3 (x = 0.45) exhibit pronounced dielectric anomalies coinciding with magnetic transitions, indicating a coupling between spin and dielectric responses. This behavior points to composition-sensitive magnetoelectric interactions, underscoring the potential for tuning multiferroic functionalities within the Ni_3−xCo_xTeO₆ solid solution.