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Giant magnetoresistance

Giant magnetoresistance (GMR) is a quantum effect observed in thin film structures with alternating ferromagnetic and nonmagnetic layers that can control electrical resistance at the nanoscale using magnetic fields. It was discovered in the late 1980s by Peter Grunberg and Albert Fert working independently, for which they received the Nobel Prize. GMR results from electron spin and magnetic moments, causing more or less scattering depending on whether the magnetic moments are parallel or antiparallel. This effect is observed at the nanoscale where the electron mean free path is greater than the interlayer separation. Main applications of GMR include magnetic field sensors for hard drives, biosensors, and MRAM as it allows control of electrical resistance with magnetic fields

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Presented To, Dr.Naeem Ahmed Submitted by, Jamil Ahmed. (642/fbas/s14.bs-physics.)
Giant magnetoresistance.  Giant magnetoresistance (GMR) is a quantum magnetorisitance effect observed in thin film structures composed of alternating ferromagnetic and non magnetic layers.  It is also a way to control the electrical resistance at the nano scale using magnetic field.
Discovery of GMR.  The Giant magnetoresistive (GMR) effect was discovered in the late 1980s by two European scientists working independently.  Awarded jointly to Peter Grunberg and Albert Fert Peter Grunberg Albert Fert
Discovery of GMR.  Multilayer's of Fe/Cr prepared by molecular beam.  Fe is ferromagnetic  material can be  permanently magnetized.  Cr is non-magnetic.  Magnetoresistive effect -50%.
Basic Theory.  Electron spin & atom magnetic moments.  On parallel- weak scattering  On antiparallel-strong scattering  More scattering= higher electrical reisitance
Why Nanoscale?  Most scattering occurs at interface of ferromagnetic and nonmagnetic layers.  Electron mean free path (10-100nm) must be greater than interlayer separation.  Current-perpendicular-plane (CPP) more effective than current-in-plane (CIP)—also more difficult to achieve.
Applications:  The main application of GMR is magnetic field sensors, which are used to read data in hard disk drives, biosensors, microelectromechanical systems (MEMS),spin value sensor, and other devices.  GMR multilayer structures are also used in magnetoresistiverandom-access memory (MRAM) as cells that store one bit of information.
Spin-Valve Senser  Find magnetic field by measuring electrical resistance. Hard Drive &Mram.  Information encoded in magnetic domains.  Reads heads sense magnetic fields: Relay information as electrical signals.  Before GMR ,hdd made of MRAM: Magnetic Ram low power induction coils and OMR. consumption,fast speed.
Summary  Up to 50% change in resistance under external magnetic field.  Nonmagnetic metal sandwiched between anti- ferromagnetically coupled layers.  Result of spin-dependent scattering, intrinsically quantum effect.  Huger impact on magnetic field sensors and hard drives.
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