Characterization of the (Cu,C)Ba<sub>2</sub>Ca<sub>3</sub>Cu<sub>4</sub>O 11+δ single crystals grown under high pressure
Chengping He, Xue Ming, Jin Si, Xiyu Zhu, Jinhua Wang, Hai‐Hu Wen
Abstract
Abstract By using a high pressure and high temperature (3.7 GPa, 1120 ∘ C) synthesis technique, we have grown (Cu,C)Ba 2 Ca 3 Cu 4 O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi/> <mml:mrow> <mml:mn>11</mml:mn> <mml:mo>+</mml:mo> <mml:mi>δ</mml:mi> </mml:mrow> </mml:msub> </mml:math> single crystals. X-ray diffraction, scanning electron microscopy, resistivity, and magnetization measurements are carried out and all show that the samples have good quality. The single crystal has onset and zero-resistance transition temperatures of about 111 and 109.6 K, indicating a very narrow transition width, which is consistent with a rather sharp magnetization transition. Magnetization hysteresis loops (MHLs) are also measured, showing a pronounced second peak effect in the intermediate temperature region. The magnetic critical current density calculated from the MHLs at 77 K and 1.5 T is about 6.4 × 10 4 A cm −2 . By using a criterion of 1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> normal state resistivity, we have determined the irreversibility line which exhibits an irreversibility field of about 8 T at 77 K. Compared with other layered systems, it is easy to find that the irreversibility line is rather high and could be further improved with the optimized transition temperature of about 118 K as previously discovered in polycrystalline samples.