Conception and search for zero magnetization ferromagnets : Novel functional materials

“A magnetically ordered system in which the conduction electron polarization can compete and cancel the contribution from its ferromagnetically aligned local magnetic moments could be termed as a ‘zero-magnetization ferromagnet’. The possibility of another somewhat different type of a ‘zero-magnetization ferromagnet’ was theoretically articulated in Samarium based compounds in the beginning era of research in rare earth intermetallics in the institute in 1970s. However, the notion of ‘zero-magnetization’ in ferromagnetic Samarium inter-metallics could be experimentally claimed and established only last year. I shall trace the story of this successful search at TIFR, which has inter alia also brought out the presence of an exchange bias (EB) field in ‘zero-magnetization spin-ferromagnets’ amongst the admixed rare earth alloys. A new class of functional materials have thus emerged that generate no self-stray magnetic field, possess large spin-polarization in conduction band and have easily tunable exchange bias field; these have the potential for niche applications in Spintronics. The present day Read-Head of a magnetic Hard-Disk is a magneto-resistance device, which essentially comprises a soft ferromagnetic layer in contact with a ferro-antiferro bi-layer assembly, imbibing the notion of an EB field.  The ‘zero-magnetization admixed RE spin-ferromagnet’ can, in principle, simply replace the multi-layer assembly having an EB attribute.”