РАЗМЕРНЫЕ ЭФФЕКТЫ В РТУТНОЙ КЕРАМИКЕ И НИОБИЕВЫХ СПЛАВАХ
Електронний архів E-archive DonNTU – (Electronic archive Donetsk National Technical University)
Переглянути архів Інформація| Поле | Співвідношення | |
| Title |
РАЗМЕРНЫЕ ЭФФЕКТЫ В РТУТНОЙ КЕРАМИКЕ И НИОБИЕВЫХ СПЛАВАХ
SIZE EFFECTS IN MERCURIC CERAMICS AND NIOBIUM ALLOYS |
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| Creator |
Русаков, Владимир Федорович
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| Subject |
намагниченность
радиочастотное поглощениe размерный эффект жесткий сверхпроводник второго рода гранулярная сверхпроводящая керамика magnetization radiofrequency absorption size effect hard superconductor of type-II granular superconductor’s ceramic |
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| Description |
В работе представлен обзор результатов, связанных с размерными эффектами, возникающими в сверхпроводящих сплавах, относящихся к жестким сверхпроводникам второго рода, в переменных внешних магнитных полях. Показано, что аномальные необратимые явления в поглощении гранулярной ртутной керамики можно объяснить наличием вихрей Абрикосова в гранулах и их влиянием на критический ток слабосвязанной среды. Пик поглощения в сверхпроводящих Nb3Al и NbTi возникает при определенном соотношении между характерным размером образца и глубиной проникновения магнитного поля. Модель размерного эффекта позволяет рассчитать сопротивление сверхпроводника в режиме течения магнитного потока.
Review of results related to size effects arising in superconducting alloys referred to hard type II superconductors in alternating external magnetic fields is presented in the paper. Magnetization and radio-frequency absorption in a plate of mercuric ceramics Hg1-xPbxBa2Ca2Cu3Oy is analyzed. Measuring of magnetization allows estimation of temperature dependence of the critical current at varied magnetic field. The results of study of radio-frequency absorption bear evidences that the observed absorption peaks are related to size effects associated with plate thickness and granules. Heterogeneous nature of high-temperature superconducting ceramics affects their magnetic and electric properties, being manifested as irreversible and non-linear phenomena. Such objects are treated as matrices of superconducting granules with Josephson bonds where grain boundaries play the role of Josephson junctions. Anomalous hysteresis is analyzed as well as increase in absorption as magnetic field decreases. It is demonstrated that anomalous irreversible phenomena in the course of absorption by granular mercuric ceramics can be explained by the presence of Abrikosov’s vortices in Josephson’s junctions and their effect on the critical current of a loosely coupled medium. The response of the critical current of Josephson’s junctions to magnetic field H, is not determined by the very magnitude of the magnetic field between the boundaries of superconducting granules, as it usually suggested, but it is controlled by surface current Jsf induced within granules. According to Maxwell equation, surface current is related to the derivative of the field H with respect to the normal to the sample surface Jsf=- . If Abrikosov’s vortices have still not penetrated the edges of a loosely coupled junction, surface current in granules Jsf coincides with Meissner screening current Jsm, which is exponentially decreasing toward the center of a granule. In this case, the critical current of Josepson junctions is determined by the standard field dependence. When Abrikosov vortices start penetrating the edges of a junction, gradient of the density of vortices emerges that generates an additional component of the surface current Jcg. At the same time, the magnitude of Meissner component of the density of surface current Jsm is controlled by the jump of induction at the interface between the intergranular space and the granule, not by the magnitude of the magnetic field in the spacing. Thus, the result is, Jsm is determined by the reversible part of magnetization of granules Meq, that is Jsm= -Meq/lg; (lg is the depth of filed penetration to granules). The analysis of the results of measurements of impedance of the superconducting polycrystal Nb3Al alloy and superconducting NbTi was carried out. The first alloy is characterized by high density of the critical current and high value of the second critical field depending on the temperature and the magnetic field. Absorption peak in superconducting Nb3Al and NbTi appears at certain ratio between the characteristic size of the sample and the depth of magnetic field penetration. The obtained results are interpreted within the frameworks of size effect model. The used model allows calculation of resistance of a superconductor in the mode of magnetic flux. |
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| Date |
2013-04-10T16:38:24Z
2013-04-10T16:38:24Z 2013 |
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| Type |
Article
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| Identifier |
2074-6652
http://ea.donntu.edu.ua/handle/123456789/18376 |
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| Relation |
Наукові праці ДонНТУ;Серія: Хімія і хімічна технологія, 2013. - Вип.1(20). - С.69-81
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| Publisher |
Донецк, ДонНТУ
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