The Nobel Prize in Physics 2007The Nobel Prize in Physics 2007Peter Grünberg“GMR can be considered one of the first real applications of thepromising field of nanotechnology ”- Nobel committeAlbert Fert
Magnetic Forces Mathematically,FB = qv x B|FB| = |qv| |B| sin θ( θ is angle between v and B)direction given by right-hand rule
Magnetic field pointing intopage (screen)Current-Carrying WireDirection of velocity v ofelectronsDirection of force onconduction electrons
Magnetoresistance - MR Electrons - moving charges Effect of external magnetic field perpendicularto the flow Force due to field pushes electrons off track
Concept Behind GMR• GMR is a completely different effect fromMagnetoresistance (MR)• MR is the regular “Lorenz” force on chargesmoving in a magnetic field• GMR exploits spin-dependent scattering
Spins and Scattering An electron moving into a magnetized regionwill exhibit spin-dependent scattering Scattering depends on direction of spinGMR is due to intrinsic rotation of the electronthat induces a magnetic moment – thequantum mechanical property called spin
Resistance and magnetizationThe straighter the path of the electrons, the greater theconductance of the material.Electric resistance is due to electrons diverging from theirstraight path when they scatter on irregularities andimpurities in the material.
Electron and its spin•Two types of spin, spin up and spin down•Spin up exhibited by majority of electrons in ferromagneticmaterials•Spin down exhibited by small amount of electrons•Spin up ultimately results in reduction in resistance, while spindown increases the resistance•Under the influence of external magnetic field most of theelectrons will be showing spin up so that R reduces
Other ApplicationsMagnetoresistive-Based Biosensors
Outcomes of GMR• Discovery of GMR opened the door to a newfield of science, magnetoelectronics (orspintronics)• CMR - Colossal MagnetoResistance,thousand-fold magnetoresistance in La–Ca–Mn–O• Magnetoelectronics & Nanotechnology.
SummarySummary• GMR effects was discovered by A. FertA. Fert and P.P.GrünbergGrünberg independently.• GMR shows large magnetoresistance.– GMR ~50 % > MR ~ a few %• The greatest contribution of GMR is the sensitivereading head for HDD.
References• J.A. Katine, F.J. Albert, and R.A. Buhrman,“Current-Driven Magnetization Reversal andSpin-Wave Excitations in Co/Cu/Co Pillars”• www.isoloop.com• www.ieee.org• https://buffy.eecs.berkeley.edu/PHP/resabs