Browsing by Author "K. Saranya"

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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.
Experimental study of multiple magnetic transitions in micrometer and nano-grain sized Ni3TeO6-type oxide
(American Institute of Physics Inc., 2020) I. Panneer Muthuselvam; K. Saranya; R. Sankar; R.N. Bhowmik; L. Kavitha
We report the experimental results of dc and ac magnetic susceptibility (χdc and χac) and specific heat (CP) measurements of the powdered Ni3TeO6-type oxide. Upon decreasing the grain size from micrometer (bulk) to nanometer range, the magnetic measurements have indicated multiple transitions, viz., a cusp at paramagnetic to ferrimagnetic (FIM) transition temperature (TC) ∼78 K, an antiferromagnetic (AFM) transition temperature (TN) ∼52 K, and a re-entrant spin glass (RSG) transition at Tm2 ∼7.49 K. The ferrimagnetic transition temperature TC is found to be highly sensitive to dc magnetic fields, where superposition of a small dc field (10 Oe) in the ac susceptibility measurement or the application of a dc magnetic field of up to 100 Oe in the dc magnetic measurement is enough to suppress the observed TC at 78 K. The CP(T) measurement also revealed a RSG state at lower temperatures for the sample with nano-sized grains. The absence of any sharp peak at TC in the CP(T) curves implies the absence of a true long-range FIM spin order in the samples. The coexistence of a RSG state with multiple magnetic transitions is understood as an effect of competitive AFM and FIM phases in the Ni3TeO6-type structure. © 2020 Author(s).
High magnetic anisotropy and magnon excitations in single crystals of the double spin chain compound PbMn2Ni6Te3 O18
(American Physical Society, 2021) I. Panneer Muthuselvam; K. Saranya; Florian Büscher; Dirk Wulferding; Peter Lemmens; Wei-Tin Chen; R. Sankar
We have successfully grown single crystals of PbMn2Ni6Te3O18 and present a comprehensive study of their magnetic, thermodynamic, and Raman spectroscopic properties. PbMn2Ni6Te3O18 consists of a planar network of pairwise rotated NiO6 dimers coupled by corners. Similarities to Ni3TeO6 exist, which forms honeycomb layers. The magnetic susceptibility χ and heat capacity Cp data reveal an antiferromagnetic phase transition around 84 K, which is evidently hysteretic on warming and cooling between 94 and 40 K with a loop width of about 1.83± 0.41 K; thus the transition appears to be of first order. χ is anisotropic, with larger values for in-plane fields over the entire measured temperature range. Raman spectroscopy has been employed to investigate the lattice and magnetic excitations of the PbMn2Ni6Te3O18 from 5 to 300 K. Besides an anharmonic phonon behavior, i.e., a decay into acoustic phonons, we find a coupling to the spin system at TN=84K, as well as weak anomalies at T∗≈200K. This second characteristic temperature gives evidence for an instability of the coupled spin/lattice system, as here the phonon linewidths and intensities evidence similar behavior as at TN=84K. Furthermore, magnetic Raman scattering at 240cm-1 is used to estimate an exchange coupling of J=-86K in general agreement with the Curie-Weiss temperature. © 2021 American Physical Society.
Magnetic order induced by magnetic impurities in the Haldane chain compound SrNi2V2O8
(Elsevier B.V., 2024) B.D. Sri Chandana; Ambili Narayanan; K. Saranya; D. Chandrasekhar Kakarla; A. Tiwari; B. Shanmugavelu; G. Peramaiyan; G. Chandra Shekar; Kwang-Yong Choi; I. Panneer Muthuselvam
Understanding the topological properties of Haldane spin systems offers promising avenues for exploring exotic quantum phases. We investigate the impact of S = 5/2 Mn2+ impurities on the magnetic properties of SrNi2V2O8, a well-known Haldane spin gapped system. Structural characterizations of SrNi2-xMnxV2O8 (x = 0.05, 0.15, 0.30 and 0.60) through Rietveld analyses of X-ray diffraction data confirm the preservation of the I41cd space group for all studied x, along with a preferential insertion of Mn2+ ions into Ni2+ sites. Magnetic susceptibility and magnetization data unveil a magnetic transition occurring in the temperature range of T = 93–99.3 K for x = 0.05–0.60. Dielectric data evince the absence of coupling between magnetic and ferroelectric phases. Notably, the magnetic ordering temperature varies little over a wide range of Mn concentrations, while notable anomalies are observed at x = 0.15. This peculiar behavior suggests that, across low-to-high concentrations, disorder-induced magnetic moments compete with the formation of spin singlets between the nearest Mn2+ impurities, which cancel out the magnetic moments. © 2024 Elsevier B.V.
Magnetic spin order in the honeycomb structured Pb6 Co9(TeO6)5 compound
(American Physical Society, 2021) I. Panneer Muthuselvam; K. Saranya; Deepa Kasinathan; R.N. Bhowmik; R. Sankar; Namasivayam Dhenadhayalan; G.J. Shu; Wei-Tin Chen; L. Kavitha; King-Chuen Lin
We present a comprehensive experimental and theoretical study of the structural, electronic, magnetic, and thermodynamic properties of a Pb6Co9(TeO6)5 single crystal. The Pb6Co9(TeO6)5 crystal has shown a unique type of magnetic spin-lattice coupling, in which the lattice structure consists of four different Co ions sites with distorted octahedral coordinations. The x-ray photoelectron spectroscopy (XPS) results confirmed the oxidation states of Pb, Co, Te, and O elements in the sample. Moreover, XPS spectra revealed the adsorbed oxygen in the defect/vacancy sites of the lattice structure. The dc magnetization measurements exhibited a complex magnetic behavior with ferrimagnetic (FIM) transition with Curie temperature TC at ∼21 K. At lower magnetic fields H, the zero-field-cooled and field-cooled curves showed a broad hump at ∼10.8 K and a shoulder peak at ∼6.2 K, which are suppressed at higher magnetic fields. The ac susceptibility data indicated spin-glass-like features. The heat capacity CP measurements confirmed the FIM transition at TC at ∼21 K, but without any trace of additional peaks at lower temperatures. The estimated Curie-Weiss constant θCW showed a peculiar field-dependent behavior along the H∥c direction of the single crystal, where θCW is less field dependent for the H⊥c direction. A large coercivity (13 kOe) is observed at 2 K for H∥c, whereas the magnetization curve of the single crystal is dominated by an antiferromagnetic feature for H⊥c. The behaviors indicate the anisotropy nature of the exchange interactions in the compound. The local spin density approximation + U total energy calculations were performed for various collinear spin configurations of a classical Heisenberg model in order to obtain the magnetic exchange interactions Ji at different distances for different neighbors. © 2021 American Physical Society.
Spin-singlet ground state of the coupled Jeff = 12 alternating chain system Sr2 Co(SeO3)3
(American Physical Society, 2022) I. Panneer Muthuselvam; R. Madhumathy; K. Saranya; K. Moovendaran; Suheon Lee; Kwang-Yong Choi; Wei-Tin Chen; Chin-Wei Wang; Peng-Jen Chen; M. Ponmurugan; Min-Nan Ou; Yang-Yuan Chen; Heung-Sik Kim; R. Sankar
We report a detailed study of the structural, magnetic, thermodynamic, and electronic properties of a coupled Jeff = 12 alternating chain Sr2Co(SeO3)3 compound using magnetic susceptibility χ(T), magnetic specific heat Cm(T), magnetization, and neutron diffraction measurements along with first-principles calculations. The first-principles calculations based on the density functional theory suggest that Sr2Co(SeO3)3 forms a quasi-one-dimensional chain with bond alternation and interchain interactions. χ(T), Cm(T), and neutron powder diffraction measurements confirm that no long-range magnetic ordering occurs down to 100 mK. Instead, a maximum in χ(T) and Cm(T) and an exponential drop of χ(T) and Cp(T) as T→0 K point to a spin-singlet ground state. The analysis of χ(T) and Cm(T) based on a J1-J2 alternating Heisenberg model shows the bond alternation α=J2/J1≈0.7 and a spin gap of Δ≈3 K. Our work demonstrates that Sr2Co(SeO3)3 is a coupled alternating chain system based on spin-orbit entangled Jeff = 12. © 2022 American Physical Society.