Magnetization studies in niobium and YBa2Cu3O7 samples |
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Authors: | B V B Sarkissian A K Grover G Balakrishnan Ravi Kumar P L Paulose R Vijayaraghavan V Sankaranarayanan C K Subramanian |
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Institution: | (1) Tata Institute of Fundamental Research, Homi Bhabha Road, 400 005 Bombay, India;(2) Department of Physics, Indian Institute of Technology, 600 036 Madras, India;(3) Present address: Centro Brasileiro de Pesquisas Fisicas -CBPF/CNPq, Rua Dr. Xavier Sigraud 150, 22290 Rio de Janeiro, Brazil;(4) Present address: Department of Physics, Panjab University, 160 014 Chandigarh, India;(5) Present address: Department of Physics, University of Warwick, CV4 7AL Coventry, UK |
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Abstract: | The results of experimental studies on hysteresis in magnetization, thermomagnetic history effects, anomalous variations in
magnetic hysteresis curves and the decay rates of magnetization obtained under different thermomagnetic histories in specimens
of conventional and high temperature superconductors are presented. The Bean’s critical state model is considered adequate
to explain magnetic behaviour in conventional hard superconductors. The similarity in the general features of the results
of different experiments on specimens of the two families of superconductors underscores the efficacy of the said model to
understand some aspects of the macroscopic magnetic response of high temperature superconductors as well. For instance, the
isothermal magnetization hysteresis loop which comprises of magnetization curves along forward (−H
max to +H
max) and reverse (+H
max to −H
max) paths define an envelop within which all isothermal magnetization data along different thermomagnetic histories lie. There
exist inequality relationship between various field values identified asH
peak,H
I,H
II etc. in isothermal magnetization hysteresis as well as magnetic relaxation data. The entire field span of an isothermal magnetization
hysteresis data set can be considered to comprise of three parts corresponding to (M
rem(H)−M
FC(H)+M
ZFC(H)) being equal to, less than or greater than zero, whereM
rem(H) are the remanent magnetization values obtained on reducing field to zero after having the specimen in different applied
field (H) values. There are, however some situations amongst thermomagnetic history effects in specimens which show incomplete flux
trapping on field cooling, where the critical state model has been found inadequate. |
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Keywords: | Magnetization curves critical current Bean’ s model anomalous magnetic behaviour time dependence of magnetization |
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