Growth and characterisation of Niobium/Gadolinium superconductor-ferromagnet nanocomposites

Abstract

Superconductivity and ferromagnetism are two antagonistic physical phenomena which their coexistence in a uniform material can be resolved only under extraordinary conditions. The reason for that is the phonon-mediated attraction energy between electrons which results in the formation of the so-called Cooper pairs, is usually smaller that the exchange (Zeeman) interaction between electrons which tend to align the electron spins. However, non-zero total momentum Cooper pairs can be accomplished even in the presence of an exchange field as surprisingly! predicted first by Fulde and Ferrel [1] and independently by Larkin and Ovchinikov [2] nearly 50 years ago. This coexistence has already been observed experimentally in both bulk samples [3, 4] and in thin films [5-7] which result from a different type of electron-pairing mechanism which electrons with spin pointing in the same direction team up to form Cooper pairs with one unit of spin, resulting in the so-called triplet superconductivity. Apart from this so-called ferromagnetsuperconductors which both superconducting and ferromagnetism order parameters are present in a uniform material, hybrid systems [8] are made form materials with different or even mutually exclusive properties. Therefore the overall property can be strongly affected by the interaction between constituent materials. The present work, concerns such a hybrid system where Nb, a superconducting metal having transition temperature below 9.5K, is placed in contact with a ferromagnetic metal, Gd with bulk Curie temperature of around 290 K in a form of a nanocomposite. The mutual immiscibility of these two elements gives us the opportunity to take advantage of both the superconduction and ferromagnetism properties of the constituents and further study the transport and magnetic behavior of the system and their effects on each other specially on the critical current of the superconductor which is expected to be modified by the proximity of the ferromagnetic metal.