Giant Magnetoresistance
Introduction
Giant Magnetoresistance (GMR) is a quantum mechanical magnetoresistance effect observed in thin film structures composed of alternating ferromagnetic and non-magnetic layers. The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR.
Discovery and Early Research
The phenomenon of GMR was first discovered in 1988 independently by two scientists, Albert Fert at the University of Paris-Sud and Peter Grünberg at the Jülich Research Centre in Germany. Their discovery was the result of research into the properties of thin film magnetic structures, a field which had been active for several decades prior to their work.
Physical Principles
The GMR effect is a quantum mechanical effect that occurs in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers. The resistance of the multilayer structure decreases significantly when the magnetization of adjacent ferromagnetic layers is aligned parallel due to spin-dependent scattering of the conduction electrons.
Spin-Dependent Scattering
The key to understanding GMR is the concept of spin-dependent scattering. In a ferromagnetic material, the conduction electrons have a preferred spin orientation. When an electron with the opposite spin orientation attempts to move through the material, it is scattered, which increases the electrical resistance. In a GMR multilayer, when the magnetization of the ferromagnetic layers is aligned, electrons with the preferred spin orientation can move through the structure with less scattering, leading to a decrease in resistance.
Applications
GMR has found numerous applications in the field of electronics and information technology. The most well-known application is in the read heads of hard disk drives. Other applications include magnetic random access memory (MRAM), magnetic sensors, and spintronic devices.