We have investigated the temperature dependence and applied magnetic-field dependences of critical current densities Jc(H, T) and the irreversibility lines Hirr(T) obtained from the magnetization measurements in HgBa2(Ca1-xSrx)2Cu3O8+δ and Hg0.5Tl0.5Ba2(Ca1-xSrx)2Cu3O8+δ. Jc(H, T) and Hirr(T) of Hg0.5Tl0.5Ba2(Ca1-xSrx)2Cu3O8+δ are found to be higher than those of HgBa2(Ca1-xSrx)2Cu3O8+δ, indicating that the Tl substitution at Hg sites provides additional flux pinning. Jc(H, T) has been analyzed using the flux-creep model. Jc(H, T) in magnetic fields above 1 T is well described by the flux-creep model. However, the thermal activation energy estimated by fitting the data to the flux-creep model shows different behaviors above and below about 65 K for both HgBa2(Ca1-xSrx)2Cu3O8+δ and Hg0.5Tl0.5Ba2(Ca1- xSrx)2Cu3O8+δ. Also, in Hirr(T) a crossover from a power-law temperature dependence above 65 K to a more rapid dependence below 65 K is observed in both samples. Although the origin of such a crossover in Hirr(T) and Jc(H, T) is not clear, the two phenomena are considered to be closely related.
Bibliographical noteFunding Information:
This work is supported by the Ministry of Science and Technology of the Republic of Korea. We appreciate K.W. Lee, C.M. Ibm, Y.S. Kim, and H.C. Lee for their technical assistance in the magnetization measurements using the DC SQUID magnetometer.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering