Critical magnetic field, lower

Studies have continued on the intercalation of the alkaline-earth metals into lattices of the transition-metal sulphides. Calcium and strontium are intercalated into M0S2 from liquid ammonia solution. X-Ray data reveal a lowering of the crystal symmetry of the sulphide and an increase in the complexity of the structure on intercalation. The intercalation compounds begin to superconduct at ca 4 K (for Ca) and 5.6 K (for Sr), and they show considerable anisotropy with respect to the critical magnetic field. Calcium in liquid ammonia also intercalates with TiS2- Two Ca,TiS2 phases have been identified. The limits of the first are 0.03 0.50, for which a relationship between x and cell parameters a and c... 

Specific resistivity p and critical temperature Tc were measured by the four-probe method. For the Tc value the point in the middle of the curve of transition to the superconducting state was taken. As a temperature sensor in the cryogenic zone a germanium thermometer of the VG-type was used. The values of the lower Hci and the upper Hc2 of the critical magnetic field at the temperature of 4.2 K were determined from differential curves of magnetization similarly to [8]. 

However, when d/(2 ) > tt/2, a second solution with 51 0 is obtained that gives lower free energy than the = 0 solution. The critical magnetic field Hp for the transition is found by equating d/(2 M)... 

Starting from these experimental facts, we will describe the characteristics of this type II SC. In these materials the superconducting electrical properties are present up to a field denoted Hc2 called the upper critical field. However, a type II SC is characterized by a stable mixed state before destruction at Hc2, existing in a certain range of magnetic field strength //cl //(7) < Hc2- Therefore the field is completely excluded only at very weak magnetic field lower than Hc this is the ideal Meissner state. 

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