Browsing by Author "Kalimuthu Moovendaran"

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Cluster-glass freezing and antiferromagnetic phase transitions in corundum structure Mg3−xCoxTeO6
(Elsevier B.V., 2023) Kalimuthu Moovendaran; Raju Kalaivanan; I. Panneer Muthuselvam; N. Rajeesh Kumar; Yen-Chung Lai; Yoshiyuki iizuka; Kwang-Yong Choi; Raman Sankar
We investigate polycrystalline powder samples of the Co-substituted Mg3−xCoxTeO6 (x = 0.0–2.4) by X-ray diffraction, magnetic susceptibilities, and specific heat. The non-magnetic parent compound Mg3TeO6 crystallizes in the trigonal R3¯ space group. All Co-substituted samples have a similar crystal structure as the parent compound. The Rietveld refinements of synchrotron X-ray diffraction data reveal distorted (Mg/Co)O6 and TeO6 octahedra. Remarkably, we find the evolution of a magnetic phase from a non-magnetic ground state to an antiferromagnetic order through a cluster glass. The antiferromagnetically ordered state emerges above the percolation threshold (x ≥ 1.0), while the cluster glass state is stabilized for x = 0.8. © 2023 Elsevier B.V.
Magnetoelectric coupling in solid solution of Ni3-xCoxTeO6 (0 ≤ x ≤ 2.85)
(Elsevier B.V., 2025) B. D. Sri Chandana; K. Karthika; K. M. Saranya; D. Chandrasekhar Kakarla; Gunasekaran Vijayasri; Jeetendra Kumar Tiwari; Kalimuthu Moovendaran; Kwang-yong Choi; K. Chandra Shekar; Raman Sankar; I. Panneer Muthuselvam
We systematically investigate the structural, magnetic, and dielectric properties of polycrystalline samples Ni3-xCoxTeO6 (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 TN ∼ 53 K and weak ferro/ferrimagnetic ordering at Tc ∼ 82 K for lower Co2+ substitution. As Co2+ content increases, TN shifts to ∼49 K, and Tc disappears at the critical concentration. For x ∼ 2.55, χ(T) reveals multiple magnetic transitions: short-range order at Tm ∼ 50 K, a cusp at TN1 ∼ 32 K, TN2 ∼ 28.3 K, and an abrupt change at 21.8 K. For higher substitution (x ∼ 2.85), these transitions shift slightly to lower temperatures, Tm ∼ 49.3 and TN2 ∼ 26.2, resembling Co3TeO6 except for the presence of Tm. 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 Ni3−xCoxTeO6 solid solution. © 2025 Elsevier B.V.
Thermal and field evolution of spin dynamics in the alternating Heisenberg Jeff= 12 spin chain Sr2 Co(SeO3)3
(American Physical Society, 2025) Suheon Lee; Wonjun Lee; Toni Shiroka; Kalimuthu Moovendaran; I. Panneer Muthuselvam; Raman Sankar; Eundeok Mun; Kwang-yong Choi
We present a comprehensive muon spin relaxation/rotation (μSR) study of the Co2+-based alternating Heisenberg Jeff=12 spin chain system Sr2Co(SeO3)3. Low-temperature magnetic property measurements confirm a spin-singlet ground state and identify two critical fields, HC1 and HC2. At HC1, the system evolves from the spin-singlet state to a canted antiferromagnetic phase, which persists up to HC2, where the system enters a fully polarized state. This magnetically ordered phase exists between μ0HC1c=2 T and μ0HC2c=3.05 T for μ0Hc and between μ0HC1///c=2 T and μ0HC2///c=3.6 T for H//c, reflecting the presence of anisotropy. Additionally, μSR results provide insights into the thermal and field evolution of spin dynamics, revealing a thermal crossover in spin correlations, the reopening of a spin gap due to anisotropy above HC1, and the emergence of a magnon gap above HC2. These findings imply the suppressed criticality of the canted antiferromagnetic phase by anisotropy. Our study establishes Sr2Co(SeO3)3 as a model system for investigating field-driven quantum phase transitions in one-dimensional Jeff=12 quantum spin chains with anisotropy. © 2025 American Physical Society.
Triangular Magnet Emergent from Noncentrosymmetric Sr0.94Mn0.86Te1.14O6Single Crystals
(American Chemical Society, 2022) Kalimuthu Moovendaran; Raju Kalaivanan; I. Panneer Muthuselvam; K. Ramesh Babu; Suheon Lee; C.H. Lee; Khasim Saheb Bayikadi; Namasivayam Dhenadhayalan; Wei-Tin Chen; Chin-Wei Wang; Yen-Chung Lai; Yoshiyuki Iizuka; Kwang-Yong Choi; Vladimir B. Nalbandyan; Raman Sankar
We report the successful growth of high-quality single crystals of Sr0.94Mn0.86Te1.14O6 (SMTO) using a self-flux method. The structural, electronic, and magnetic properties of SMTO are investigated by neutron powder diffraction (NPD), single-crystal X-ray diffraction (SCXRD), thermodynamic, and nuclear magnetic resonance techniques in conjunction with density functional theory calculations. NPD unambiguously determined octahedral (trigonal antiprismatic) coordination for all cations with the chiral space group P312 (no. 149), which is further confirmed by SCXRD data. The Mn and Te elements occupy distinct Wyckoff sites, and minor anti-site defects were observed in both sites. X-ray photoelectron spectroscopy reveals the existence of mixed valence states of Mn in SMTO. The magnetic susceptibility and specific heat data evidence a weak antiferromagnetic order at TN = 6.6 K. The estimated Curie-Weiss temperature θCW = -21 K indicates antiferromagnetic interaction between Mn ions. Furthermore, both the magnetic entropy and the 125Te nuclear spin-lattice relaxation rate showcase that short-range spin correlations persist well above the Néel temperature. Our work demonstrates that Sr0.94(2)Mn0.86(3)Te1.14(3)O6 single crystals realize a noncentrosymmetric triangular antiferromagnet. © 2022 American Chemical Society.