Interplay of magnetism and superconductivity in a new band magnetic superconductor Y₉Co₇

Abstract

Till very recently, all the known magnetic superconductors contained magnetic rare earth ions and they could be viewed as a sublattice of magnetic ions immersed in and weakly coupled to the host superconducting matrix. The discovery) of definite unambiguous coexistence of magnetism and superconductivity in a purely transition metal binary viz. Y₉Co₇ (initially thought to be "Y₄Co₃") has added a new dimension to this field. The most distinguishing feature of this system is that the onset of magnetism precedes that of superconductivity and on further lowering the temperature the two phenomena build up together. The bulk magnetic and transport studies) suggest that the magnetism is of itinerant kind and the sources of magnetism and superconductivity cannot be considered delinked as in the earlier rare earth based systems. neutron depolarization studies on Y₉Co₇ have resulted in some very spectacular new results, the significance of which have as yet not been fully comprehensible. The spread of superconductivity to the bulk of the sample affects magnetism but does not quench it. Externa; pressure results in pushing the sritical balance between the critical balanse between superconductivity and magnetism towards the former and the replacement of > 2 atomic percent of Co by Ni enhances magnetism. All the curious properties known so far were illustrated and their significance discussed.