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Magnetic Memory in a Ceramic YBCO Superconductor Composed of Sub-micron-size Grains
Hiroyuki Deguchi,Takuya Ashida,Mitsuhiro Syudo,Masaki Mito,Seishi Takagi,Makoto Hagiwara,Kuniyuki Koyama 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
The ceramic YBa2Cu4O8 (YBCO) composed of sub-micron-size grains is considered as a randomJosephson-coupled network of 0 and junctions and shows successive phase transitions. The firsttransition occurs inside each grain at Tc1 = 81 K, and the second transition occurs among thegrains at Tc2 = 47 K. A magnetic glass behavior similar to those of spin-glasses is observed attemperatures below Tc2. The memory phenomena are investigated by recording the zero-fieldcooledand thermoremanent magnetizations measured on heating after the cooling process witha halt at Ts = 41 K. Memory effects of the halt are imprinted in the system when the sampleis re-heated. In the case without a field switch at Ts, the influence of the halt is confined to anarrow temperature region near Ts whereas the memory effect of the halt employing a field switchis extended over a wide temperature region below Ts. The results suggest that chiral-glass orderingoccurs at Tc2 in the ceramic YBCO.
Shuhei Yamaguchi,Nobuhiro Yamaguchi,Masaki Mito,Hiroyuki Deguchi,Peter. J. Baker,Stephen. J. Blundell,Michael. J. Pitcher,Dinah. R. Parker,Simon. J. Clarke 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
The pressure effects on the 111-type Fe-based superconductor LiFeAs were investigated throughAC susceptibility measurements and X-ray diffraction experiments, and revealed a correlation betweenthe superconducting transition temperature (Tc) and the As-Fe-As bond angle (α) ratherthan the height of As from the Fe layers (hAs). As the pressure was increased, Tc of 17 K at P =0 GPa decreased down to 10 K at P = 5.2 GPa. According to a previous report from an X-raydiffraction experiment, α changes from 101.5˚ at 0 GPa to 97.8˚ at 17 GPa. The obtained changein Tc is consistent with Lee et al.’s plot of Tc as a function of α, and from this result, we concludethat Tc will fall to zero at around α = 98˚.
Synthesis and Magnetic Properties of DyMnO3 Nanoparticles in Mesoporous Silica
Takayuki Tajiri,Atsushi Kohno,Kenta Hamamoto,Yuhki Ando,Hiroyuki Deguchi,Masaki Mito 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We synthesized nanoparticles of the perovskite manganite DyMnO3 in pores of mesoporous silicaSBA-15 and investigated their magnetic properties. X-ray diffraction patterns of the nanoparticlesindicated successful synthesis of the DyMnO3 nanoparticles with a particle size of about 10 nmin the pores of SBA-15. The temperature dependence of the DC magnetic susceptibility for theDyMnO3 nanoparticles exhibited a pronounced magnetic irreversibility between the field-coolingand the zero-field-cooling susceptibility due to the blocking phenomena and indicated a change ofthe magnetic exchange interactions from those for the bulk crystal. The in-phase susceptibility χ" and the out-of-phase susceptibility χ" of the AC susceptibility for the nanoparticles exhibited apeak at the blocking temperature, and that peak shifted toward higher temperature with increasingfrequency. Magnetization curves for the nanoparticles were reproduced by using a Langevin functionand exhibited a hysteresis loop at temperatures below the blocking temperature. Magnetic sizeeffects and superparamagnetic behaviors were observed in the DyMnO3 nanoparticles.