Browsing by Author "Wei-Tin Chen"

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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.
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 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.
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.