page_title: Giant magnetoresistance
section_title: General principle
hierarchical_section_title: Giant magnetoresistance / Applications / Spin-valve sensors / General principle
caption_attribution_description: Deutsch: Nachbau: Der erste GMR-Sensor von Prof. Dr. Peter Grünberg in seiner Testvorrichtung. Dieses originalgetreue Replikat wurde von Innomag e.V. - dessen Schirmherr Grünberg ist - im April 2007 auf der Hannover Messe ausgestellt. Das Original ist im Deutschen Museum in München. An den Enden der Versuchsbank ist jeweils ein zylindrischer Permanentmagnet montiert. Dazwischen, nahe der Mitte sitzt der schwarze GMR-Sensor oben am Schlitten; von unten greift ein Mitnehmer in die helixförmige Nut (Rechtsgewinde) der Messingwelle ein. Wird diese per Drehknopf gedreht, wird mit dem Schlitten der Sensor verschoben. Je nach Position im inhomogenen Magnetfeld wirkt eine andere Feldstärke und kann ein veränderter elektrischer Widerstand am Sensor gemessen werden. Über den örtlichen Verlauf kann die Abhängigkeit des Widerstands vom B-Feld untersucht werden. English: Replicate of the first GMR Sensor (black, on top of the slider on the bench, its position between two magnets can be changed) made by Peter Grünberg. The original one is in Deutsches Museum in Munich.
context_page_description: Giant magnetoresistance is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers. The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR.
  The effect is observed as a significant change in the electrical resistance depending on whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel alignment. The overall resistance is relatively low for parallel alignment and relatively high for antiparallel alignment. The magnetization direction can be controlled, for example, by applying an external magnetic field. The effect is based on the dependence of electron scattering on the spin orientation.
  The main application of GMR is magnetic field sensors, which are used to read data in hard disk drives, biosensors, microelectromechanical systems and other devices. GMR multilayer structures are also used in magnetoresistive random-access memory as cells that store one bit of information.
context_section_description: One of the main applications of GMR materials is in magnetic field sensors, e.g., in hard disk drives and biosensors, as well as detectors of oscillations in MEMS. A typical GMR-based sensor consists of seven layers:
  Silicon substrate,
  Binder layer,
  Sensing (non-fixed) layer,
  Non-magnetic layer,
  Fixed layer,
  Antiferromagnetic (Pinning) layer,
  Protective layer.
  The binder and protective layers are often made of tantalum, and a typical non-magnetic material is copper. In the sensing layer, magnetization can be reoriented by the external magnetic field; it is typically made of NiFe or cobalt alloys. FeMn or NiMn can be used for the antiferromagnetic layer. The fixed layer is made of a magnetic material such as cobalt. Such a sensor has an asymmetric hysteresis loop owing to the presence of the magnetically hard, fixed layer.
  Spin valves may exhibit anisotropic magnetoresistance, which leads to an asymmetry in the sensitivity curve.
caption: A copy of the GMR sensor developed by Peter Grünberg
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