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Hole doping of MgB2C2, a MgB2 related [B/C] layered compound
Takao Mori,Eiji Takayama-Muromachi 한국물리학회 2004 Current Applied Physics Vol.4 No.2-4
The MgB2 related borocarbide MgB2C2 was synthesized and various attempts were made to hole dope the material. MgB2C2 is orthorhombic (space group Cmca a= 10:92 A,b= 9:45 A,c= 7:45 A) with [B/C] nets. Successful synthesis was carried out frompure elements by a solid state reaction method in a closed environment. Theoretical calculations indicate the possibility of holedoping of MgB 2C2 to be favorable for superconductivity due to the at band (in theTYdirection) similar to one in MgB2. Holedoping of MgB 2C2 was attempted by two routes: (1) substitutional dope of Mg with alkali metals, (2) doping in the [B/C] nets, andas a result Li doping was indicated to be feasible with a possible semiconductor to metal transition induced. High pressure synthesisof (Mg,Li)B2C2 was also attempted but only resulted in formation of the LiBC phase.
Pressure-induced Metal-insulator Transition of the Mott Insulator Ba2IrO4
Daisuke Orii,Masafumi Sakata,Atsushi Miyake,Katsuya Shimizu,Hirotaka Okabe,Masaaki Isobe,Eiji Takayama-Muromachi,Jun Akimitsu 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
The electrical resistivity of single crystals of the spin-orbit Mott insulator Ba2IrO4 has beenmeasured at pressures up to 30 GPa and at temperatures from 100 mK to 300 K. Ba2IrO4 showsa metal-insulator transition at around Pc = 24 GPa, though it does not show superconductivitydown to 100 mK. The low-temperature resistivity in the metallic state does not obey a conventionalFermi-liquid description. This suggests that carriers are incoherently scattered by antiferromagneticquantum spin fluctuations. The critical exponent for the metal-insulator transition is about 1.6,indicating that Ba2IrO4 is located near the boundary between a Mott and an Anderson insulator. This means that even in a single crystal, the effect of crystallographic disorder should not be ignored.
Magnetic Frustration Effects in the New Colossal Magnetoresistance Oxide NaCr2O4
Hikaru Takeda,Yasuhiro Shimizu,Masayuki Itoh,Hiroya Sakurai,Eiji Takayama-Muromachi 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We have investigated the magnetic properties of the new colossal magnetoresistance oxideNaCr2O4 with the calcium-ferrite-type structure by using 23Na, 53Cr nuclear magnetic resonance(NMR) and magnetization measurements. This chromate is found to show an antiferromagneticorder with the spin moments slightly canted from the b axis at temperatures below TN=125 K. The spin structure may be governed by the competition between double-exchange ferromagneticand superexchange antiferromagnetic interactions in the double chains. The origin of the largemagnetoresistance is discussed for several scenarios such as phase separation, rearrangement of thespin structure induced by the magnetic field, and domain walls.