Browsing by Author "K. Ramesh Babu"

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Anisotropic Magnetic Properties of Nonsymmorphic Semimetallic Single Crystal NdSbTe
(American Chemical Society, 2020) Raman Sankar; I. Panneer Muthuselvam; Karthik Rajagopal; K. Ramesh Babu; G. Senthil Murugan; Khasim Saheb Bayikadi; K. Moovendaran; Chien Ting Wu; Guang-Yu Guo
The crystal structure and magnetic, electronic, and thermal properties of a NdSbTe single crystal were examined by X-ray diffraction, magnetic and specific heat Cp(T) measurements, and density functional theory (DFT) calculations. NdSbTe undergoes an antiferromagnetic ordering at TN ≈ 2.9 K, which is obviously shown from χ(T) and Cp(T). With increasing H, a spin-flop transition is induced along the c axis, and subsequently AFM disappeared at H ≤ 0.4 T and H ≤ 2.5 T along H≈c and H≈ab, respectively. This remarkable observation shows that the ordered Nd3+ moments lie in the c axis and that there is the existence of an anisotropy scenario. The estimated magnetic anisotropy with χ≈c (0.63)/χ≈ab (0.036) is 17.5 at temperature 1.8 K. An analysis of specific heat capacity reveals the significant contribution of crystal field effects at high temperature. We carried out DFT calculations to predict the magnetic ground state and the electronic properties of NdSbTe. Our calculations revealed that the magnetic ground state is AFM with spins aligned ferromagnetically along the b axis and antiferromagnetically along the c axis. The calculated electronic band of NdSbTe exhibits a Dirac semimetal material nature. © 2020 American Chemical Society.
Crystal growth and magnetic properties of the coupled alternating S =1 spin chain Sr2Ni(Se O3)3
(American Physical Society, 2023) R. Madhumathy; K. Saranya; K. Moovendaran; K. Ramesh Babu; Arpita Rana; Kwang-Yong Choi; Heung-Sik Kim; Wei-Tin Chen; M. Ponmurugan; R. Sankar; I. Panneer Muthuselvam
The structural, magnetic, and thermodynamic properties of a quasi-one-dimensional (1D) S=1 alternating spin chain compound Sr2Ni(SeO3)3 are investigated by using synchrotron x-ray powder diffraction, magnetic susceptibility χ(H,T), and heat capacity CP(H,T) measurements together with density functional theory (DFT) calculations. The χ(H,T) and CP(H,T) data reveal long-range antiferromagnetic order at TN=3.4(3) K and short-range order at Tm≈7.8K. The short-range magnetic order together with 95% of spin entropy release above TN signifies the importance of 1D spin correlations persisting to ∼8TN. Theoretical DFT calculations with generalized gradient approximation determine leading exchange interactions, suggesting that interchain interactions are responsible for the observed long-range magnetic ordering. In addition, the temperature-field phase diagram of Sr2Ni(SeO3)3 is determined based on the χ(T,H) and CP(T,H) data. Interestingly, a nonmonotonic phase boundary of Tm is found for an external field applied along a hard axis. Our results suggest that the ground state and magnetic behavior of Sr2Ni(SeO3)3 rely on the interplay of single-ion anisotropy, bond alternation, and interchain interactions. © 2023 American Physical Society.
Magnetic and structural dimer networks in layered K2Ni (MoO4)2
(American Physical Society, 2021) G. Senthil Murugan; K. Ramesh Babu; R. Sankar; W.T. Chen; I. Panneer Muthuselvam; Sumanta Chattopadhyay; K.-Y. Choi
The magnetic and thermodynamic properties of layered single-crystal K2Ni(MoO4)2 having both structural and magnetic dimers have been investigated. The crystal structure of K2Ni(MoO4)2 is composed of edge-sharing NiO6-octahedral pairs bridged by the MoO42- polyatomic ion groups in a plane, and the K+ ions sit in the van der Waals gap between the layers. The temperature dependence of magnetic susceptibility shows a spin-singlet ground state with an activation gap of Δ/kB≈38 K. A high-field magnetization study at T=1.5 K exhibits a half-magnetization plateau at μ0H∼25 T, corresponding to a level crossing of the singlet ground state with the lowest triplet state. Further, we have performed density functional theory calculations to determine magnetic exchange interactions. The nearest-neighbor coupling constant J1∼10 K between the Ni spins turns out to be an order of magnitude larger than all interdimer couplings. Our experimental and theoretical results suggest that K2Ni(MoO4)2 constitutes a nearly isolated two-dimensional S=1 dimer model. © 2021 American Physical Society.
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.