Регулярный семинар аспирантов и молодых ученых КФТИ Вторник 15. 0 0

Регулярный семинар аспирантов и молодых

ученых КФТИ

Вторник 15.00

1.Цели и задачи

2.Структура докладов

3.Пожелания к презентациям

4.Обязательная информация при подготовке к докладу

5.Слушатели

1.Научиться выступать с докладами и делать презентации

2.Получить информацию о проблемах, объектах и методах

3.«Обкатать» выступления на конференциях, защитах и т.п.

4.Учебные лекции сотрудников института и гостей

1.Цели и задачи

1.Заголовок, автор2.План3.Краткий обзор проблемы, мотивация

4.Описание исследуемой системы.5.Используемый метод6.Полученные результаты7.Выводы8.Заключение, планы, благодарности, список соавторов





Vanadium Oxide Nanotubes(VOx-NT)

Vanadium Oxide Nanotubes(VOx-NT)

Electron Spin Resonance inElectron Spin Resonance in

Yulieth Cristina Arango, IFW-DresdenYulieth Cristina Arango, IFW-Dresden

Leibniz Institutefor Solid State andmaterials researchDresden




● Motivation ● Why VOx-NTs are interesting?

● Introduction● Morphology and structure of VOx-NT

● Basic principles on ESR

● Experimental data and discussion● VOx-NTs – Temperature dependence in ESR

and

comparison with magnetization

data

● Influence of Lithium doping - ESR

measurements

● Conclusions & Outlook

● Motivation ● Why VOx-NTs are interesting?

● Introduction● Morphology and structure of VOx-NT

● Basic principles on ESR

● Experimental data and discussion● VOx-NTs – Temperature dependence in ESR

and

comparison with magnetization

data

● Influence of Lithium doping - ESR

measurements

● Conclusions & Outlook

OutlineOutline




Why VOx-NT becomes interestingWhy VOx-NT becomes interestingNanoscale magnetic materials novel aspects in

magnetic structure and dynamic on the nanometer scale

VOx-NT and its character of mixed valence vanadium

oxide

Mixed valenceMixed valence

coexistence of two valence states

V4+ V5+and

3d1 3d0Configurations of a partially

filled d-shell

ferromagnetism by ferromagnetism by doping with either doping with either electrons or holeselectrons or holes

Strong electronic correlations in the spin and

charge sectors

transition-metal (TM) oxide low-D structural units

based on

Nanoscale materials


4.Описание исследуемой системы.

5.Используемый метод6.Полученные результаты7.Выводы8.Заключение, планы, благодарности, список соавторов


TEM

Inner diameters:Inner diameters:Between 20 and 30 nmBetween 20 and 30 nm

VOx-layer

Organic molecules Organic molecules Dodecylamine, CDodecylamine, C1212HH2525NHNH22

TEM image of VOx-NT

Outer diameter:Outer diameter:Range from 50 to 100 nmRange from 50 to 100 nm

Synthesis &Synthesis & MorphologyMorphology

Hydrothermal procedure

Multiwall NT+

scroll

Two dimensional quasi-tetragonal

cell

side view

O

V

Distorted Distorted octahedronoctahedron

tetrahedrontetrahedron

VV77OO1616 layer layeredge-sharing VO-Octahedra edge-sharing VO-Octahedra coupled in zig- zag chainscoupled in zig- zag chainsisolated VO-Tetrahedraisolated VO-Tetrahedra

O V

StructureStructure

Electron diffraction pattern

Similar structure Similar structure

in BaVin BaV77OO1616 xx nH nH22O O

mixed valency

60% V4+ [3d1] , magnetic (S = ½)40% V5+ [3d0] , non-magnetic (S = 0)

Core level photoemission(XPS) data from the V 2p levels of VOx-

NT

Increase in the number of the 3d electrons

Vanadium valenceVanadium valence

V 2p

VO2

V2O5

V4+

V5+

V4.4+Binding energy in-between

14% free spins14% free spins Tetrahedral coordinationTetrahedral coordination+ 28% spins coupled in dimers28% spins coupled in dimers+ 18% spins coupled in trimers 18% spins coupled in trimers Octahedral coordinationOctahedral coordination

Expected:Expected:

Found:Found: (Magnetization and NMR measurements)

downshift the binding energy

}




BgBU B2

1

The energy separation of the two spin states:

Zeeman Energy: Describes the Interaction between the spin and the field.

g-factor

Spin susceptibility

Electron Spin Resonance ESRElectron Spin Resonance ESR

SBe g

Electron magnetic moment

Absorption: PAbsorption: P

dP/dHdP/dH

Spin-spininteracti

on

Bg B2

1

Bg B2

1

0B

RF-inducedtransition

Energy

Increasing magnetic field B

h

H0

Hres:

Line-width:

Area:Spin angular momentum

2

1 , ssz mmS

Effective magnetic field experienced by each Effective magnetic field experienced by each electronelectron

SIAHHSLHH Zcfˆ.ˆˆ.ˆ0

Electron-electroninteraction

Spin-orbit coupling

Hiperfine Coupling

Crystal field Zeeman interaction

3d

En

erg

y3

d E

nerg

y eg eg

t2g t2g

2L+1 = 5

2L+1 = 5

3z2-r23z2-r2x2-y2x2-y2

xzxzxyxy yzyz

x2-y2x2-y2

3z2-r23z2-r2

xyxy

xzxz yzyz

b1t b1t

a1t a1t

b2t b2t

et et

free Vanadiumfree Vanadium V4+ in cubic symmetryV4+ in cubic symmetry

V: [Ar] 3d3 4s2[3d1], S=1/2

V

O

V

O

V4+ in tetragonal symmetryV4+ in tetragonal symmetry

V




2000 3000 4000 5000

-10

-5

0

5

10Line 1:g

1 = 2.00

free spins

dP

/dH (a.

u.)

Field (G)

Experiment T=300 K

Total Fit

Line 2:g

2 = 1.97

trimers dimers at high temp.

g2

g1

ESR Signal from VOx-NanotubesESR Signal from VOx-Nanotubes

Two Lorentzian linesTwo Lorentzian lines

Two nonequivalent magnetic

V4+ (S = 1/2) sites

Line 1: Individual V spins in tetrahedral positions Line 2: spin trimers and

thermally excite spin dimers in distorted octahedral positions

X-band ESRX-band ESR 9.52 GHz9.52 GHz

Field = 0 G to 9000 GField = 0 G to 9000 G

Broad lineBroad lineBroad lineBroad line

Narrow lineNarrow line

0 50 100 150 200 250 3000

100

200

300

400

500

600

700

800

dimers

quasi-free spinstrimers

Line

widt

h (G

)

Temperature (K)

Narrow line Broad line

0 50 100 150 200 250 300

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

dimerstrimers(narrow line)

Inv.

Are

a(no

rm.

RT) -

(a.u

)

Temperature (K)

ESR Magnetization

quasi-free spins(broad line)

0 50 100 150 200 250 3001.96

1.98

2.00

2.02

2.04

2.06

dimers

quasi-free spinstrimers

g-fa

ctor

Temperature (K)

Narrow line Broad line

Quasi-free spinsin V(3)-sites

DimersDimers

(thermall(thermall

y y activatedactivated

))

DimersDimers

(thermall(thermall


))

= 4.4 K= 4.4 K

Dimers in the chainsHigh temperature

Trimers in the chains

14 %

28 %

18 %

DimersDimers

(thermall(thermall


))

DimersDimers

(thermall(thermall


))




Undoped VOx-NTs:Undoped VOx-NTs:

Different spin species identified by ESRDifferent spin species identified by ESR- Individual spins- Individual spins Equal amount Equal amount - Trimers- Trimers

- Dimers- Dimers Thermally activated above 100 KThermally activated above 100 KGood agreement with Magnetization measurements and NMRGood agreement with Magnetization measurements and NMR

Li-doped VOx-NTs:Li-doped VOx-NTs:

Focus on the Ferromagnetic sample Li = 0.1Focus on the Ferromagnetic sample Li = 0.1

- Individual spins and trimers present- Individual spins and trimers present- Dimers do not survive- Dimers do not survive- Additional narrow line - Additional narrow line Ferromagnetic resonance ??Ferromagnetic resonance ??

ConclusionsConclusions

}

1.Заголовок, автор2.План3.Краткий обзор проблемы, мотивация4.Описание исследуемой системы.5.Используемый метод6.Полученные результаты7.Выводы8.Заключение, планы, благодарности, список соавторов


- Determine Li position (X-rays)Determine Li position (X-rays)

- Spin dynamics vs. Lithium concentration by ESR Spin dynamics vs. Lithium concentration by ESR and NMRand NMR

- Confront ferromagnetismConfront ferromagnetism

- ESR on newly prepared samplesESR on newly prepared samples

- High field ESR (Good spectral resolution)High field ESR (Good spectral resolution)

OutlookOutlook

B. Büchner, V. Kataev

Christian, Ferenc, Uwe and Mohammed from the ESR group

Christine Täschner, Andreia Ioana Popa, Rüdiger Klingeler, Ingo Hellmann, Jenia Vavilova

B. Büchner, V. Kataev

Christian, Ferenc, Uwe and Mohammed from the ESR group

Christine Täschner, Andreia Ioana Popa, Rüdiger Klingeler, Ingo Hellmann, Jenia Vavilova

Financial support by the Alban OfficeFinancial support by the Alban OfficeFinancial support by the Alban OfficeFinancial support by the Alban Office

AcknowledgementsAcknowledgements

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3.Пожелания к презентациям

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2000 3000 4000 5000

-10

-5

0

5

10

dP

/dH (a.

u.)

Field (G)

Experiment T=300 K

Total Fit


2000 3000 4000 5000

-10

-5

0

5

10

dP

/dH (a.

u.)

Field (G)

Experiment T=300 K

Total Fit




V4+ (S = 1/2) sites

Line 1: g=2.0 Individual V spins in tetrahedral positions

Line 2: g=1.97 spin trimers and thermally excite spin dimers in distorted octahedral positions



2000 3000 4000 5000

-10

-5

0

5

10Line 1:g

1 = 2.00

free spins

dP

/dH (a.

u.)

Field (G)

Experiment T=300 K

Total Fit

Line 2:g

2 = 1.97

trimers dimers at high temp.

g2

g1




V4+ (S = 1/2) sites

Line 1: Individual V spins in tetrahedral positions Line 2: spin trimers and

thermally excite spin dimers in distorted octahedral positions



Broad lineBroad lineBroad lineBroad line

Narrow lineNarrow line

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[email protected]@[email protected]

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Регулярный семинар аспирантов и молодых ученых КФТИ Вторник 15. 0 0