Molecular SpintronicsPhysical Chemistry using Spin-Orbit Interaction

Research Center for SpectrochemistryJun Okabayashi jun@chem.s.u-toko.ac.jp

2020. 5. 22 物理化学特論 II

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Spinelectronics (Spintronics)

transport

light

Spin-dependentdevices

Magnetism Semiconductor

Opto-electric devices and circuit

Quantum computing

Quantum communication

Optical isolator

Quantum calc. Sensor

Non-volatile memory

Spin Adding novel functionalities

Spin controllingCarrier controlling

Light controlling

spinstorage Amprifer

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What spintronics had done ? What is next?

Prof. A. Fert Prof. P. Grunberg

Novel prize in 2007

Discovery of giant magnetoresistance(GMR)(1986)

HDD with large memory size

Industry of MRAMHigh density HDD

Tunnel magnetoresistance(TMR)(1994)Tohoku univ. Prof. Miyazaki

What is next ?

Spin RAM

Large size storage

Quantum computor

Spin optical memory

Spin transistor

Spintronics with physical chemistry

GMR

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Orbitronics

Giant Magneto Resistance (GMR)

Baibich et al.: PRL 62 (1988) 2472

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５

Tunnel magnetoresistance (TMR) using Magnetic Tunnel Junction (MTJ)

Parallel Anti-Parallel

F I F TMR is a fundamental principle for non-volatile memory.

Novel electronics without dissipation by spin currents

Charge current Spin current

Devise design using spin torque and domain wall motion

Spin-Hall effect (SHE)

Conduction is independent on lattices.

Ｉ↑＋Ｉ↓ Ｉ↑- Ｉ↓

Magnetic field(SOI)

６

Electric current

Spin current

Motion of spin Spin dynamics

No energy dissipation !

Electric current and spin current

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Information transfer using spin wave

Spin wave transfer using insulator Y3Fe5O12

８

ＭＲＡＭ

Manipulation of information using write and read linesmagnetic layer: non-volatile

TMR devices connected on the transistor

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Magnetization reversal using spin injection！

Not magnetic field but current or voltage can be utilized for spin controlling!

Field

Current

Magnetic field writing MRAM

Current

Spin injection type MRAM (SPRAM)

10

8

6

4

2

0

Writ

ing

curr

ent (

mA

)

0.01 0.1 1Memory cell size (µm)

10

8

6

4

2

0

Writ

ing

curr

ent (

mA

)

0.01 0.1 1Memory cell size (µm)

MRAM

Gbit

107 A/cm2

SPRAMMbit ~kbit

９

Magnetic Random Access Memory (MRAM)

新しい概念による動作の創製 （たとえば、核スピン利用）

MRAM

高品質TMR素子開発

Field

Current

DRAM SRAM Flash FeRAM MRAM

データ保持機構 電荷 電荷 電荷 誘電分極 磁化

不揮発性 × × ○ ○ ○

読み出し形式 破壊 非破壊 非破壊 破壊 非破壊

読み出し時間(ns)

30 3 20-120 30-200 10-50

書き込み時間(ns)

30 2 1×106 30-200 10-50

書換え可能回数 >1015 >1016 106 1010 >1016

セルサイズ 8 F2 70 F2 4.4 F2 80 F2 10 F2

容量(b)/D. R. (µm)

25 M/

0.175

4 M/ 0.25

1 G/

0.1632 M/0.2 1 M/0.6

用途PC main

PC携帯buffer

携帯電話memory card

IC card 汎用

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Spin-Hall effect (SHE)

Magnetic field(Spin-orbit interaction）

Spin Hall Effect

By using spin orbit interaction, spin distribution changes without magnetic field.

Y. Kato et al. Science 306, 1910 (2004).

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The scales of less than spin diffusion length are required for spintronics devices because spins are not conserved and scattered.

Charge

Spin

Spin diffusion length < 10 μm

：Charge conservation

：Spin scattering by HLS

Ranges where spins operate

Quantum infrmation

• Nanoscaled fabrication for spintoronics14

Future in SpintronicsInterfaces between magnetic layer: spintronics field(ultra-high density recording media, low energy consumption)

Interfacial spin-orbit coupling -> Spin-Orbitronics

What is the next ?-> Quadrupoles

磁性金属

非磁性金属

In-plane Out-of-plane漏れ磁場なし、熱安定性よし

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Slater-Pauling curves

Three important points in Slater-Pauling curves;Less than half : bcc, increased magnetic momentsMore than half: fcc, decreased magnetic momentsWhat is the origin of the branch ?

Electron number

Mag

netic

mom

ent (

u B)

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Graphene Spintronics

グラファイト1層からなる2次元層 バンド構造が特異的：Schrodinger方程式ではなく、Dirac方程式に従うスピン拡散長が長いのが利点

高い移動度

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Graphene is consisted by single layer.High mobility in light mass of carbon

• Schrödinger equation (non-relativity)

• Relativity formulation

22( ) ( )

2ri r

t mψ ψ∂

= − ∇∂

2

2pm

ε =

it

ε ∂↔

∂ p i↔ − ∇

2 2 2 2 2 2( ) ( )x y zp p p m ccε

+ + − = −

it

ε ∂↔

∂ p i↔ − ∇

？spin

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From molecular orbitals to band structures

熱との戦い

From Intel web pageFrom wikipedia

Tran

sist

or c

ount

s on

circ

ular

chi

ps

Year of introduction

Controlling of Spins and orbitals can be breakthrough.

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Operation of MOS-FET

小長井誠 半導体物性 培風館Q26: Summarize the MOS-FET transister operation.

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Single Molecular Magnet : Mn12

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Lapo Bogani & Wolfgang Wernsdorfer, Nature Materials 7, 179 - 186 (2008)

Application for Molecular Spintronics

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Lapo Bogani & Wolfgang Wernsdorfer, Nature Materials 7, 179 - 186 (2008)

Spin transister using SMM

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What is synchrotron radiation ?

http://en.wikipedia.org/wiki/Synchrotron_light_source

Linearc

Storage ring

Acceleration ring

Synchrotron radiationBrightPolarizedTunable photon energy

Electron beam orbits are bent by magnetic field.

Generation of synchrotron radiation

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Research Center for Spectrochemistry (RCS), The University of Tokyo

RCS has a beam line at Photon Factory in KEK.

BL-7A: Bending magnet is used. Energy ranges of hv=50-1300 eV are obtained.

Suitable for K-edge absorption for C, N, and O, L-edge absorption for transition metals, and high-resolution core-level photoemission spectroscopy

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スペクトルセンターのビームライン

Spin-orbit interactionElectrons round the central nuclear, resulting the generation of currents.Spin-orbit interaction promotes to split j=l+1/2, j=l-1/2. Intensity ratios; l+1 : l Degeneracy; 2j+1電子が原子核の回りを運動することにより円電流を感じ、磁場を生じる。スピン軌道相互作用；j=l+1/2, j=l-1/2 に分裂

強度比；l+1 : l (縮退度2j+1の比に対応）

HSO=ζ(l・s)= ζ/2 (j2-l2-s2)

j=l+1/2; E(l+1/2) = 1/2 ζh2lj=l-1/2; E(l-1/2) = -1/2 ζh2(l+1)

ζ=0 ζ≠0

j=l+1/22(2l+1)

j=l-1/2

縮退度2l+2 (2j+1)

2l (2j+1)

1/2ζh2l

1/2ζ h2(l+1)

軌道 量子数 面積比l j

s 0 1/2 __p 1 1/2 1

1 3/2 2d 2 3/2 2

2 5/2 3f 3 5/2

3 7/2 4

1.0

0.8

0.6

0.4

0.2

0.0

-106 -104 -102 -100 -98eVBinding Energy (eV)

Si 2p2p3/2

2p1/2

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Chemical shift of core-level spectra

Origin of chemical shift

∆EB=k∆q + ∆V - ∆ER

q : chargeV = Σqj/Rj ：Madelung potential（Sum of static potential around ligand) ER : Relaxation energy(Screening of core hole）

Li - Li2O Fe compounds

Chemical Shift occurs by the valence states and photoelectron emission process.

表面分析技術選書「X線光電子分光法」（丸善）

価電子が結合に使われると内殻電子の原子核への束縛は強くなる。

プラス価数が増えると高結合エネルギー側へシフトする。

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XPS of Polyethylene terephthalate (PET)

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Induced Magnetism in Pt cluster30

Non-magnetic Pt atoms in clusters behave as magnets !(Surface effect)

C60-Co分子のXMCD測定

Y. Matsumoto et al. Chem. Phys. Lett. 470, 244 (2009)

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Angle-Resolved Photoemission Spectroscopy (ARPES)

XPS of Graphene on Cu

ARPES of Graphene on Cu

José Avila et al., Sci. Rep. 3, 2439 (2013).

ARPES of Graphene 33

A. Varykhalov et al., Phys. Rev. Lett. 101, 157601 (2008).

Q:Explain about the principles of ARPES.

Q:Explain about the properties of graphene.

Topological insulators34

C60 Spintronics 35