giant magneto resistance (gmr)

Giant Magneto ResistanceGiant Magneto Resistance(GMR)(GMR)

2007 10/30論文紹介

by 白鳥昂太郎( ちなみに去年は 10/31 発表でした )

PaperPaper

The Nobel Prize in Physics 2007The Nobel Prize in Physics 2007

Albert Fert Albert Fert (( アルベール・フェールアルベール・フェール ))

Unité Mixte de Physique Unité Mixte de Physique CNRS/THALES, Université CNRS/THALES, Université Paris-Sud, Orsay, FranceParis-Sud, Orsay, France(( 国立科学研究センター国立科学研究センター (CNRS)(CNRS) の科学の科学主任 主任 (( とタレスグループ合同科学主とタレスグループ合同科学主任 任 ))))

Peter GrünbergPeter Grünberg(( ペーター・グリューンベルクペーター・グリューンベルク ))

Forschungszentrum Jülich, GermanyForschungszentrum Jülich, Germany(( 独ユーリヒ固体物理研究所教授独ユーリヒ固体物理研究所教授 ))

This year's physics prize is awarded for the technology that is used to read 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 data on hard disks. It is thanks to this technology that it has been possible to miniaturize hard disks so radically in recent years. miniaturize hard disks so radically in recent years. Sensitive read-out headsSensitive read-out heads are needed to be able to read data from the compact hard disks used in laptops are needed to be able to read data from the compact hard disks used in laptops and some music players, for instance. and some music players, for instance.

ContentsContents

• Backgrounds– Ferromagnetic metals– Magneto Resistance

– Giant Magneto Resistance

• HDD• Summary

BackgroundsBackgrounds

Ferromagnetic metals Ferromagnetic metals (( 強磁性体強磁性体 ))

S↓ S↓S↑ S↑

W/o Magnetic field W/ Magnetic field

The 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: 遷移金属 )

Parallel: Energy → decreasedAnti-parallel : Energy → increased

Magneto ResistanceMagneto Resistance• Resistance : 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 metals– The 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 : R/R ~a few %.

Giant Magneto ResistanceGiant Magneto ResistanceFe | Cr | Fe layersFe | Cr | Fe layersCr (non-ferromagnetic metalsferromagnetic metals) sandwiched by Fe (ferromagnetic metalsferromagnetic metals)

I↑:FM-3d → NFM-3d: R 大 ,large

NFM-3d → FM-3d: R 小 ,small

I↓:FM-3d → NFM-3d: R 小 , small

NFM-3d → FM-3d: R 大 ,large

⇒ Larger resistance

B↑ B↑

Current : IFM→NFM→FM

I↑:FM-3d → NFM-3d: R 大 , large

NFM-3d → FM-3d: R 大 , large

I↓:FM-3d → NFM-3d: R 小 , small

NFM-3d → FM-3d: R 小 , small

⇒ Smaller resistance

Giant Magneto ResistanceGiant Magneto Resistance

B↑ B↑

Fe | Cr | Fe layersFe | Cr | Fe layersCr (non-ferromagnetic metalsferromagnetic metals) sandwiched by Fe (ferromagnetic metalsferromagnetic metals)

Experimental resultExperimental result

R/R ~1.0 R/R ~1.0 ⇒ ⇒ 0.5 (50 % changed)0.5 (50 % changed)

GMR @ Half-metalGMR @ Half-metal

CrO2

: Only one electron state for conductivity at the Fermi level→By the magnetic field, one spin direction state dose not shows the conductivity.

The multilayer material shows strong GMR effects.

TMR : Tunneling magnetoresistanceTMR : Tunneling magnetoresistance

The 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.R/R ~500 % increasedR/R ~500 % increased大　野　研　究　室　大　野　研　究　室　(( 池田准教授研究室）池田准教授研究室）

東北大学電気通信研究所 ナノスピン実験施設東北大学電気通信研究所 ナノスピン実験施設

GMR researchGMR research

• Discovery of GMR– The begging of Spintronics– Sensitive magnetic probe

• Technological background– Development of nano-technology– Growth of lattice (Epitaxial growth)

• The greatest contribution ⇒ HDD

HDDHDD

Requirements for HDDRequirements for HDD

• Compact size and fast reading– The 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 HDDProperty of HDD

• ハードディスクドライブ– 出典 : フリー百科事典『ウィキペディア

（ Wikipedia ）』• Present capacity of HDD

– ~200 GBit/inch2 (25 GB/inch2)

inch2= 500 円 coin size*First HDD ~4 MB

@ Refrigerator size

Future growthFuture growth

• GMR head ⇒ TMR head

• MRAN– Magnetic working Random Access Memory– MARN combines RAM with HDD.

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 sensitive reading head for HDD.

• The TMR effect is based on the idea of GMR.– More sensitive reading head is being developed.