Let me start with this quote, “The theory of metallic resistance abounds in mysteries,” rightly said by Meaden (1971). One of these mysteries is about how and why electrical resistance changes when a magnetic field acts on ferromagnetic materials. And these questions have been driving a huge buzz in the scientific community, especially since the discovery of Giant MagnetoResistance (GMR) in magnetic multi-layers (Fe) separated by nonmagnetic conducting spacer (Cr).
Albert Fert and Peter Grunberg independently discovered the GMR effect in 1988 [1, 2] and won the 2007 Nobel Prize in physics for their work. Interestingly, their discovery was quickly followed by intense work — especially by IBM Almaden researchers — as a result, we have wonderful new products: high storage devices on our computers and notebooks, i-Pods, mobile phones. All within 20 years following a major new discovery!
The pioneering work of Fert and Grunberg also led to the birth of a new field called spintronics (a word coined by S.A. Wolf in 1996). Here’s spintronics in a nutshell: unlike in normal electronics, where only the electron charge is used, spintronics exploit the spin degree of freedom of electrons to store, encode, access, process and/or transmit information in some way.
Soon after the discovery of GMR many devices were proposed. Of those, the most famous is the Datta-Das spin field-effect transistor (SFET); others include race track (domain wall motion ) memory by IBM, Magnetic Random Access Memories (MRAM), spin dependent tunneling devices (tunneling magneto resistance devices), quantum computing and many more sensors based on GMR.
In the coming posts starting with GMR I will be taking up each one of these applications and go into relevant details with a focus on materials aspects and challenges faced by materials scientists in synthesis of these materials. Until then I sign off with the following “free to access” links on spintronics.
1. M. Baibich et al., Phys. Rev. Lett. 61, 2472 (1988).
2. Binasch, G., P. Gru¨ nberg, F. Saurenbach, and W. Zinn, 1989,‘‘Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange,’’ Phys. Rev. B 39, 4828–4830.
Free spintronics links. These are not behind any pay wall!
marcuslab.harvard.edu/spinvalve/Baibich1988.pdf (same as Ref 1)
PS : I sincerely thank Abi for his generous suggestions on my pre-post version of this blog article.