Browsing by Author "Raju Kalaivanan"

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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.
Spin dynamics and 1/3 magnetization plateau in the coupled distorted diamond chain compound K2Cu3(MoO4)4
(American Physical Society, 2025) G. Senthil Murugan; Joydev Khatua; Suyoung Kim; Eundeok Mun; K. Ramesh Babu; Heung-sik Kim; C. L. Huang; Raju Kalaivanan; U. Rajesh Kumar; I. Panneer Muthuselvam; Wei Tin Chen; Sritharan Krishnamoorthi; Kwang-yong Choi; Raman Sankar
We investigate magnetic properties of the s=1/2 compound K2Cu3(MoO4)4 by combining magnetic susceptibility, magnetization, specific heat, and electron spin resonance (ESR) with density functional calculations. Its monoclinic structure features alternating Cu2+ (s=1/2) monomers and edge-shared dimers linked by MoO4 units, forming a distorted diamond chain along the a axis. Antiferromagnetic order occurs at TN=2.3 K, as evident from a λ-type anomaly in specific heat and magnetic susceptibility derivatives. Inverse magnetic susceptibility reveals coexisting ferro- and antiferromagnetic interactions. Specific heat and ESR data show two characteristic temperatures: one at 20 K, associated with spin-singlet formation in Cu2O9 dimers, and another at 3.68 K, indicating short-range correlations between dimers and monomers. Magnetization measurements reveal a metamagnetic transition at 2.6 T and a critical magnetic field μ0Hc=3.4 T, where a 1/3 magnetization plateau emerges with saturation near 0.35 μB. Low-temperature specific heat and magnetization data reveal the suppression of long-range order at μ0Hc, enabling the construction of a temperature-magnetic field phase diagram showing multiple magnetic phases near the μ0Hc. Density functional theory confirms a distorted diamond chain with J1 dimers and competing J2, J4, J3, and J5 interactions with monomer spins as an effective low-temperature spin model. © 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.