Browsing by Author "Eundeok Mun"

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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.
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.