Junhoe Kim

Oxygen deficiency as a driving force for metamagnetism and large low field magnetocaloric effect in La0.7Ca0.3−xSrxMnO3−δ manganites

We report the importance of metamagnetism for the giant magnetocaloric effect in lanthanum manganites and the key role of oxygen deficiency for this phenomenon. It is found that La0.7Ca0.3−xSrxMnO3−δ samples with x=0.0, 0.025, 0.05, 0.075, 0.1, and 0.125 are orthorhombic (O) phase, while those with x=0.15, 0.175, 0.2, and 0.3 are rhombohedral (R) phase at room temperature. The samples possess relatively high oxygen deficiency δ. With increasing x, the oxygen content increases from about 2.92 to 2.94 in the O phase and from 2.93 to 2.97 in the R phase, while it decreases in the vicinity of the O-R phase transition. The Curie temperature increases with increasing x in both the structural phases and shows a positive jump around the O-R phase transition. The x=0 sample shows S-shape magnetization, which is typical for metamagnetic materials. The S shape is continuously suppressed with increase in Sr and disappears for x≥0.075. Interestingly, the magnetic entropy change, adiabatic temperature change, and refri...

Coupled gyration modes in one-dimensional skyrmion arrays in thin-film nanostrips as new type of information carrier

We report on a micromagnetic numerical simulation study of dynamic coupling between neighboring skyrmions periodically arranged in narrow-width nanostrips. We explored the coupled gyration modes and their characteristic dispersions in terms of the interdistance between the neighboring skyrmions. The application of perpendicular magnetic fields allows for the control and modification of the dispersion of the coupled gyration modes. The coupled gyration modes of individual skyrmions might provide a new type of information carrier in narrow-width straight and curved nanostrips, as driven by magnetic interactions in such continuous thin films.

X-ray absorption near-edge structure spectra study of the Ba1−xKxBiO3 (0.37⩽x⩽1.0) superconductor

Abstract X-ray absorption near-edge structure spectra (XANES) of the Ba 1− x K x BiO 3 (BKBO) (0.37⩽ x ⩽1.0) superconductor have been measured at the Bi L III edge. To estimate changes of the Bi valence state, and reveal its influence on the superconducting properties of this solid solution, quantitative spectral characteristics of the 2p 3/2 →6s transition in the series comprising different Ba/K ratios were determined. The superconducting transition T c of the BKBO samples, determined from dc magnetic susceptibility measurements, monotonously decreases from Ba 0.63 K 0.37 BiO 3 ( T c =30.4 K) to Ba 0.26 K 0.74 BiO 3 (a very low diamagnetic signal was detected at T ∼3 K). This corresponds to the increase of Bi valence determined from XANES data in the range +4.36⩽ ν ⩽+4.74. Further increase of the K content to x >0.8 results in reappearance of superconductivity with T c =9 K. The maximum value of formal Bi valence versus K content corresponds with the minimum in T c .

Robust magnon-photon coupling in a planar-geometry hybrid of inverted split-ring resonator and YIG film

We experimentally demonstrate strongly enhanced coupling between excited magnons in an Yttrium Iron Garnet (YIG) film and microwave photons in an inverted pattern of split-ring resonator (noted as ISRR). The anti-crossing effects of the ISRR’s photon mode and the YIG’s magnon modes were found from |S21|-versus-frequency measurements for different strengths and directions of externally applied magnetic fields. The spin-number-normalized coupling strength (i.e. single spin-photon coupling)

Anomalous reentrant resistance phenomena in superconducting Sr1-xKxBiO3: Recovery of superconductivity with electric or magnetic field

{g}_{{\rm{eff}}}/2\pi \sqrt{N}

Coupled breathing modes in one-dimensional Skyrmion lattices

geff/2πN was determined to 0.194 Hz (

Synthesis and electrical transport of Hg0.8Tl0.2Ba2Cu3O8+σ

{g}_{{\rm{eff}}}/2\pi