Giant Magneto Resistance(GMR)2007 10/30by
The Nobel Prize in Physics 2007Albert Fert ()Unit Mixte de Physique CNRS/THALES, Universit Paris-Sud, Orsay, France((CNRS) ( ))
Peter Grnberg()Forschungszentrum Jlich, Germany()This year's physics prize is awarded for the technology that is used to read data on hard disks. It is thanks to this technology that it has been possible to miniaturize hard disks so radically in recent years. Sensitive read-out heads are needed to be able to read data from the compact hard disks used in laptops and some music players, for instance.
ContentsBackgroundsFerromagnetic metalsMagneto ResistanceGiant Magneto ResistanceHDDSummary
Ferromagnetic metals ()SSSSW/o Magnetic fieldW/ Magnetic fieldThe characteristic of Ferromagnetic metals are determined from the behavior of the valence electrons under the Fermi surface.The magnetization occurs from the polarization of those electrons.Ex. Fe, Co, Ni : 3d and 4s electrons (Transition metals:)Parallel: Energy decreasedAnti-parallel : Energy increased
Magneto ResistanceResistance : The scattering of conduction electrons by the vibration of lattice The electrical resistance has no difference between spin-up and spin-down electrons.
Resistance of transition metalsThe conductivity of transition metals are mainly determined by 4s electrons.4s electrons can be scattered into 3d states. Resistance of transition metals (For Cu, all 3d states are occupied and it shows high conductivity) Scattering process (resistance) is related to the spin-orbital transition.
By the magnetic field, the scattering process of ferromagnetic metals can be changed. Spin-up electrons feel the different resistance from Spin-down ones.(The electronics considering the spin direction of electrons is called spintronics.)
Magnet resistance : DR/R ~a few %.
Giant Magneto ResistanceFe | Cr | Fe layersCr (non-ferromagnetic metals) sandwiched by Fe (ferromagnetic metals)I:FM-3d NFM-3d: R,largeNFM-3d FM-3d: R,smallI:FM-3d NFM-3d: R, smallNFM-3d FM-3d: R,large Larger resistanceBBCurrent : IFMNFMFMI:FM-3d NFM-3d: R, largeNFM-3d FM-3d: R, largeI:FM-3d NFM-3d: R, smallNFM-3d FM-3d: R, small Smaller resistance
Giant Magneto ResistanceBBFe | Cr | Fe layersCr (non-ferromagnetic metals) sandwiched by Fe (ferromagnetic metals)
Experimental resultDR/R ~1.0 0.5 (50 % changed)
GMR @ Half-metalCrO2: Only one electron state for conductivity at the Fermi levelBy the magnetic field, one spin direction state dose not shows the conductivity.
The multilayer material shows strong GMR effects.
TMR : Tunneling magnetoresistanceThe insulating material has only a few atomic layers thick.The probability of the tunneling through the insulator is large.
The resistance can be changed by the external magnetic field as similar the GMR effects.DR/R ~500 % increased (
GMR researchDiscovery of GMRThe begging of SpintronicsSensitive magnetic probe
Technological backgroundDevelopment of nano-technologyGrowth of lattice (Epitaxial growth)
The greatest contribution HDD
Requirements for HDDCompact size and fast readingThe size of magnetized area should be small. It is difficult to read the direction of magnetization (binary) because of its weakness.Writing :Reading :
The sensitive head is needed to achieve the compact HDD.GMR head
Property of HDD: WikipediaPresent capacity of HDD ~200 GBit/inch2 (25 GB/inch2)inch2= 500 coin size*First HDD ~4 MB @ Refrigerator size
Future growthGMR head TMR headMRANMagnetic working Random Access MemoryMARN combines RAM with HDD.
SummaryGMR effects was discovered by A. Fert and P. Grnberg independently.
GMR shows large magnetoresistance.GMR ~50 % > MR ~ a few %
The greatest contribution of GMR is the sensitive reading head for HDD.
The TMR effect is based on the idea of GMR.More sensitive reading head is being developed.