Kwang‐Yong Choi

We report pulsed field magnetization and ESR experiments on a {Cu3} nanomagnet, where antiferromagnetically coupled Cu(2+) (S = 1/2) ions form a slightly distorted triangle. The remarkable feature is the observation of a half step magnetization, hysteresis loops, and an asymmetric magnetization between a positive and a negative field in a fast sweeping external field. This is attributed to an adiabatic change of magnetization. The energy levels determined by ESR unveil that the different mixing

We report inelastic light-scattering experiments on ${\text{CaFe}}_{2}{\text{As}}_{2}$ in the temperature range of 4--290 K. In in-plane polarizations two Raman-active phonon modes are observed at 189 and $211\text{ }{\text{cm}}^{\ensuremath{-}1}$, displaying ${A}_{1g}$ and ${B}_{1g}$ symmetries, respectively. Upon heating through the tetragonal-to-orthorhombic transition at about ${T}_{S}=173\text{ }\text{K}$, the ${B}_{1g}$ phonon undergoes a discontinuous drop of frequency by $4\text{ }{\text

Abstract Recent success in experimental and theoretical works on metal thiophosphates (MTPs) paved the way to add multiple functionalities of complex oxides, such as ferroelectricity, in 2D materials. To realize multiferroicity and magnetoelectric coupling on layered van der Waals materials, incorporating magnetic ions in the ferroelectric framework is desirable. Unfortunately, replacing the metal ion with a magnetic one in MTPs results in antiferroelectricity in which spontaneous macroscopic po

We report Raman-scattering measurements on the quasi-two-dimensional quantum spin system ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{Cu}}_{2}({\mathrm{BO}}_{3}{)}_{2}$ $(x=0$ and 0.1) in interlayer polarizations and temperatures between 5 K and 450 K. Upon approaching the structural phase transition at ${T}_{s}=395\mathrm{K},$ a strong anharmonic softening of an interlayer mode at $62{\mathrm{cm}}^{\ensuremath{-}1}$ is observed together with overtone features and a broadening of i

We report on coherent manipulation of electron spins in an antiferromagnetically coupled spin triangle ${{\mathrm{Cu}}_{3}\mathrm{\text{\ensuremath{-}}}X}$ ($X=\mathrm{As}$, Sb) impregnated in freestanding nanoporous silicon (NS) by using 240 GHz microwave pulses. Rabi oscillations are observed and the spin coherence time is found to be ${T}_{2}=1066\text{ }\text{ }\mathrm{ns}$ at 1.5 K. This demonstrates that the ${{\mathrm{Cu}}_{3}\mathrm{\text{\ensuremath{-}}}X}\mathrm{\text{:}}\mathrm{NS}$ h

We report on pulsed-field magnetization, $Q$-band electron spin resonance (ESR), and $^{23}\mathrm{Na}$ NMR measurements of the $S=1∕2$ spin triangle clusters ${\mathrm{Na}}_{9}[{\mathrm{Cu}}_{3}{\mathrm{Na}}_{3}{({\mathrm{H}}_{2}\mathrm{O})}_{9}{(\ensuremath{\alpha}\text{\ensuremath{-}}X{\mathrm{W}}_{9}{\mathrm{O}}_{33})}_{2}]$ ($X=\mathrm{As}$ and Sb). The pulsed-field magnetization shows pronounced hysteresis loops and magnetization steps including the half-step magnetization. The detailed ma

Quantum spin liquids are outstanding examples of highly quantum entangled phases of matter and serve as a testbed to gauge central concepts of strongly correlated materials. Enormous research efforts in the past few decades have brought an in-depth understanding of these novel phases, although their conundrums have not yet been solved completely. In this review, we give an overview of the three different classes of spin-liquid materials: (i) a one-dimensional spin chain system KCuF₃,

Raman scattering studies of the frustrated spin chain system ${\mathrm{LiCu}}_{2}{\mathrm{O}}_{2}$ are reported. Two transitions into a magnetically ordered phase (taken place at temperatures $\ensuremath{\sim}9$ and $\ensuremath{\sim}24\mathrm{K})$ have been confirmed from the analysis of optical properties of the samples. Interestingly, two different magnetic excitations, seen at 100 and $110{\mathrm{cm}}^{\ensuremath{-}1}$ in the magnetically ordered phase superimpose each other independently

We report on polarized Raman scattering of single crystals of Nd1−xSrxMnO3 (x = 0.3, 0.5). Raman spectra of Nd0.7Sr0.3MnO3 show a significant change through the metal–insulator transition. In the ferromagnetic metallic phase phonon modes grow in intensity and number while the electronic continuum becomes more pronounced. We suggest that these effects are due to the strong competition between the localization and the delocalization of carriers which is the origin of the largest colossal magnetore

We present an inelastic light scattering study of single crystalline ${({\mathrm{La}}_{1\ensuremath{-}y}{\mathrm{Pr}}_{y})}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ ($0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.14$, $y=0$ and $x=1∕8$, $0\ensuremath{\leqslant}y\ensuremath{\leqslant}0.5$). A giant softening up to $20--30\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ of the $\mathrm{Mn}\ensuremath{-}\mathrm{O}$ breathing mode has been observed only for the fe

We report on the magnetic susceptibility and Raman scattering measurements of the S = 1/2 three-dimensional (3D) spin web compound Cu3TeO6. The magnetic susceptibility shows an antiferromagnetic ordering at T-N similar to 61 K and a deviation from the Curie-Weisslaw around 150 K. Raman spectra show the emergence of a new mode at 132 cm(-1) for temperatures below T * similar to 50 K (approximate to 0.8 T-N). At the same temperature, phonon anomalies in intensity and frequency show up. This gives