Nam Hwi Hur

Excellent magnetocaloric properties of La0.7Ca0.3−xSrxMnO3(0.05⩽x⩽0.25) single crystals

This letter reports on the superior magnetocaloric properties of La0.7Ca0.3−xSrxMnO3 (x=0.05, 0.10, 0.20, and 0.25) single crystals. Upon 50 kOe applied field, the magnetic entropy changes (ΔSM) reach values of ∼10.5, 7.45, 6.97, and 6.86J∕kgK for x=0.05, 0.10, 0.20, and 0.25 compositions, respectively. The large magnetic entropy changes have been found to occur around 300 K, thus allowing magnetic refrigeration at room temperature. Due to the absence of grains in the single crystals, the ΔSM distribution here is much more uniform than that of gadolinium and polycrystalline manganites, which is desirable for an Ericson-cycle magnetic refrigerator. The single crystals have the large magnetic entropy changes induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials. These results indicate that the present single crystals are excellent candidates as working materials for AMR.

Large magnetocaloric effect in a La0.7Ca0.3MnO3 single crystal

We report the results of a thorough study of the magnetocaloric effect (MCE) in a La0.7Ca0.3MnO3 single crystal, which undergoes a first-order magnetic phase transition at ∼227 K. The magnetic entropy change ΔSM and the adiabatic temperature change ΔTad reach, respectively, ∼6.42 J/kg K and 4.76 K for ΔB=5 T and even if both are smaller than those exhibited by gadolinium (∼9.8 J/kg K and ∼11.7 K), the ΔSM distribution here is much more uniform than that of gadolinium and polycrystalline manganites. This is desirable for an Ericson-cycle magnetic refrigerator. The MCE is larger in the single-crystalline manganite compared to the polycrystalline one. The manganite single crystal has large ΔSM induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials. All these make the lanthanum manganite single crystal an attractive candidate as a working substance for AMR. The molecular field model provides a fairly good description of the magnet...

Strain-induced magnetic stripe domains in La0.7Sr0.3MnO3 thin films

We have investigated magnetic microstructures of magnetoresistive La0.7Sr0.3MnO3 (LSMO) thin films. Magnetic images are strongly dependent on structural strain induced by the substrates. The LSMO film on SrTiO3 dominated by tensile stress effect displays a feather-like pattern, whereas LSMO films on LaAlO3 and NdGaO3 substrates under compressive stress show stripe domains. In particular, the magnetic image of the film on NdGaO3 reveals distinctive straight stripe domain patterns on the order of about 120 nm, suggesting the presence of a sizable out-of-plane magnetization. The ordering of the stripe domains is also sensitive to the field direction.

Oxygen pressure and thickness dependent lattice strain in La0.7Sr0.3MnO3 films

We report magnetic and electronic properties of La0.7Sr0.3MnO3 (LSMO) thin films epitaxially grown on perovskite substrates by pulsed laser deposition, which are varied with oxygen background pressure and film thickness. The strains of the LSMO films are tuned by the two parameters but their resulting effects are somewhat different. The lattice strain induced by the oxygen pressure suppresses the ferromagnetic transition (TC) and metal–insulator transition (TMI) temperatures. With decreasing film thickness from 110 to 11 nm, however, small changes in both TC and TMI were observed. These results suggest that the physical properties of the LSMO films are strongly dependent on the oxygen content but less sensitive to the film thickness.

Ligand Effects on Luminescence of New Type Blue Light-Emitting Mono(2-phenylpyridinato)iridium(III) Complexes

Newly prepared hydrido iridium(III) complexes [Ir(ppy)(PPh3)2(H)L](0,+) (ppy = bidentate 2-phenylpyridinato anionic ligand; L = MeCN (1b), CO (1c), CN(-) (1d); H being trans to the nitrogen of ppy ligand) emit blue light at the emission lambda(max) (452-457, 483-487 nm) significantly shorter than those (468, 495 nm) of the chloro complex Ir(ppy)(PPh3)2(H)(Cl) (1a). Replacing ppy of 1a-d with F2ppy (2,4-difluoro-2-phenylpyridinato anion) and F2Meppy (2,4-difluoro-2-phenyl-m-methylpyridinato anion) brings further blue-shifts down to the emission lambda(max) at 439-441 and 465-467 nm with CIE color coordinates being x = 0.16 and y = 0.18-0.20 to display a deep-blue photoemission. No significant blue shift is observed by replacing PPh3 of 1a with PPh2Me to produce Ir(ppy)(PPh2Me)2(H)(Cl) (1aPPh 2Me), which displays emission lambda max at 467 and 494 nm. The chloro complexes, [Ir(ppy)(PPh3)2(Cl)(L)](0,+) (L = MeCN (2b), CO (2c), CN(-) (2d)) having a chlorine ligand trans to the nitrogen of ppy also emit deep-blue light at emission lambda(max) 452-457 and 482-487 nm.

Thermal relaxation of field-induced irreversible ferromagnetic phase in Pr-doped manganites

We have investigated the magnetic and transport properties of

Hollow nickel-coated silica microspheres containing rhodium nanoparticles for highly selective production of hydrogen from hydrous hydrazine

{\mathrm{Pr}}_{0.65}{\mathrm{Ca}}_{0.35}{\mathrm{MnO}}_{3}

Synthesis of azines in solid state: reactivity of solid hydrazine with aldehydes and ketones.

and

Isolation and structural characterization of the elusive 1:1 adduct of hydrazine and carbon dioxide

{\mathrm{Pr}}_{0.82}{\mathrm{Na}}_{0.18}{\mathrm{MnO}}_{3}

Raman studies on single-phasic HgBa2CuO4+δ superconductors

with almost the same doping level under various magnetic fields. Upon applying a field of 4 T, both compounds undergo a metamagnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) in the low-temperature region. The field-induced FM state is very stable for at least