Magnetostrictive, magnetic, and transport properties of correlated electron systems

Abstract

The main objective of the present work is the investigation of the vortex state in type II superconductors using the magnetostriction technique as a tool together with other, complementary methods.<br />In this context, the possibilities of magnetostriction as well as its limitations have been intensively studied. Its staticity and its resolution especially at high magnetic fields have proven to be extremely useful in the study of the 'peak effect' region and thermomagnetic history dependence effects.<br />Measurements on both polycristalline NbTi and single crystalline 2H-NbSe2 samples have been performed. A comparative study of scaling in the peak region and at intermediate magnetic fields shows that the non-applicability of scaling laws at high fields does not have to be considered as a hallmark of an anomalous peak effect. Geometrical scaling of the field range of coexistence of the stable ordered and the disordered vortex phases evidence against a first order thermodynamic phase transition into the peak region. A new type of magnetic history dependence at low and intermediate magnetic fields has been found and tentatively ascribed to the propagation of metastable vortex structures.