Inhomogeneities in magnetic systems Inhomogeneous magnetic systems: - - PowerPoint PPT Presentation

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Inhomogeneities in magnetic systems Inhomogeneous magnetic systems: - - PowerPoint PPT Presentation

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European School on Magnetism 2009 Inhomogeneities in magnetic systems Inhomogeneous magnetic systems: control and applications Alberta Bonanni Institute for Semiconductor and Solid State Physics, Johannes Kepler University, Linz Austria

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SLIDE 1

Inhomogeneities in magnetic systems

Alberta Bonanni

Institute for Semiconductor and Solid State Physics, Johannes Kepler University, Linz – Austria

European School on Magnetism 2009

Inhomogeneous magnetic systems: control and applications

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SLIDE 2

Control over magnetic ions aggregation

Strain

e.g. vertical alignement of InAs QDs in GaAs

G.Springholz et al. Science 282, 734 [1998]

PbSe/Pb1-xEuxTe superlattices

Review: J.Stangl, V.Holý, G.Bauer, Rev.Mod.Phys. 76, 689 [2004]

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SLIDE 3

Ways to control the aggregation of TM

1] growth rate

L.H. Ye and A. Freeman, Phys.Rev. B 73, 81304 [2006]

2] growth temperature

  • T. Dietl, Nature Mat. 5, 673 [2006]

3] co-doping with donors or acceptors

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SLIDE 4

Unique aspect of our material systems:

▪ d-levels in the gap ▪ contribute to the bonding ▪ foster attractive force between magnetic ions ▪ kinetic barrier to the formation of ferromagnetic nanocrystals

By changing the valency

▪ modification of the attractive force ▪ influence on the magnetic ions aggregation

Why aggregation of magnatic ions?

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SLIDE 5
  • A. Bonanni et al. Phys.Rev.Lett. 101, 135502 [2008]

3] co-doping with donors or acceptors

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SLIDE 6

Control by co-doping

▪ TM-related states reside in the host band gap ▪ charge state and intersite Coulomb repulsion can be changed by co-doping with shallow impurities ▪ the Coulomb repulsion between TM ions hinders spinodal decomposition

Fe+3 EF GaN GaN:Si GaN:Mg

  • T. Dietl, Nature Mat. 5, 673 [2006]
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SLIDE 7

Control by co-doping

▪ TM-related states reside in the host band gap ▪ charge state and intersite Coulomb repulsion can be changed by co-doping with shallow impurities ▪ the Coulomb repulsion between TM ions hinders spinodal decomposition

Fe+3 EF GaN EF Fe+2 GaN:Si GaN:Mg

  • T. Dietl, Nature Mat. 5, 673 [2006]
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SLIDE 8

Control by co-doping

▪ TM-related states reside in the host band gap ▪ charge state and intersite Coulomb repulsion can be changed by co-doping with shallow impurities ▪ the Coulomb repulsion between TM ions hinders spinodal decomposition

Fe+3 EF GaN EF Fe+2 GaN:Si EF Fe*4= Fe+3 + h GaN:Mg

  • T. Dietl, Nature Mat. 5, 673 [2006]
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SLIDE 9

N-doped

50nm

Optimized

N-doped Inhomogeneous Homogeneous

10

20

10

21

100 200 300

TC ΘP

Critical Temp. [K] [N] [cm

  • 3]

100 200 300

ΘP Critical Temp. [K]

240220200 180 160 140 120TCdI2 [

  • C]

10

19

10

18

10

17

TB TC

[ I ] [ cm

  • 3]

(Zn,Cr)Te – effect of codoping on Cr distribution

  • S. Kuroda et al., Nature Mater. 6, 440 [2007]
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SLIDE 10

Effect of Si-doping

Quenching of ferromagnetic response

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SLIDE 11

Effect of Si-doping [on secondary phases]

Quenching of ferromagnetic response Reduction/dissolution of secondary phases * *

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SLIDE 12

Effect of Si-doping [on chemical decomposition]

Quenching of ferromagnetic response Reduction/dissolution of chemical decomposition

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SLIDE 13

Si doping – effect on Fe charge state

(Ga,Fe)N:Si – synchrotron XANES

  • M. Rovezzi, ..AB, ...Phys.Rev. B 79, 195209 [2009]
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SLIDE 14

Si doping – effect on Fe charge state

(Ga,Fe)N:Si – synchrotron XANES

Fe3+

  • M. Rovezzi, ..AB, ...Phys.Rev. B 79, 195209 [2009]
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SLIDE 15

Si doping – effect on Fe charge state

(Ga,Fe)N:Si – synchrotron XANES

Fe3+

  • M. Rovezzi, ..AB, ...Phys.Rev. B 79, 195209 [2009]
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SLIDE 16

Si doping – effect on Fe charge state

(Ga,Fe)N:Si – synchrotron XANES

Fe3+ Fe3+

  • M. Rovezzi, ..AB, ...Phys.Rev. B 79, 195209 [2009]
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SLIDE 17

Si doping – effect on Fe charge state

(Ga,Fe)N:Si – synchrotron XANES

Fe3+ Fe2+ Fe3+

  • M. Rovezzi, ..AB, ...Phys.Rev. B 79, 195209 [2009]
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SLIDE 18
  • A. Bonanni et al. Phys.Rev.Lett. 101, 135502 [2008]

Co-doping and TM aggregation

summary

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SLIDE 19

Outlook

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SLIDE 20
  • M. Jamet et al., Nature Mat. 5, 653 [2006]

Outlook: self-organized nanocolumns

Ge1-xMnx

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SLIDE 21
  • M. Jamet et al., Nature Mat. 5, 653 [2006]

Outlook: self-organized nanocolumns

  • L. Gu et al., JMMM 290, 1395 [2005]

(Al,Cr)N Ge1-xMnx

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SLIDE 22
  • G. Meier et al., Phys.Rev.Lett. 98, 187202 [2007]

Domain walls for 3D memories

electric current induces the shift of magnetic regions along a wire HD does not need to spin

increased data storage and speed Unclear: how to fabricate dense arrays of required nanocolumns self-organized nanocolumns in DMS [?]

Self-organized nanomagnets in semiconductors

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SLIDE 23
  • P. Nam-Hai et al., Nature 458, 489 [2009]

Spin-battery – GaAs:MnAs

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SLIDE 24

▪ nanometallization:

nanoelectronics, optoelectronics, plasmonics ▪ large magnetotransport effects field sensors ▪ large magnetooptical effects

  • ptical isolators, tunable photonic crystals

▪ spintronic structures high density MRAMs/race track memories/logic

▪ spin battery

▪ large spin entropy thermoelectricity

Functionalities

  • P. Nam-Hai et al., Nature 458, 489 [2009]
  • H. Katayama-Yoshida et al.,

Jpn.J.Appl.Phys 46, L777 [2007]

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SLIDE 25

R.E. Lechner, and G. Bauer

Institute for Semiconductor Physics, Johannes Kepler University, Linz – Austria

  • Z. Matěj, and V. Holý
  • Dept. of Cond. Matter Physics, Charles University, Prague – Czech Republic
  • M. Rovezzi, and F. D‘Acapito

INFM, GILDA ESRF beamline, Grenoble – France

  • W. Stefanowicz, M. Kiecana, R. Jakieła, M. Sawicki, and T. Dietl

Institute of Physics, Polish Academy of Sciences, Warsaw – Poland

  • A. Navarro-Quezada, B. Faina, T. Li, M. Wegscheider, D. Leite, A. Grois

and T. Devillers

Institute for Semiconductor Physics, Johannes Kepler University, Linz – Austria

In collaboration with

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SLIDE 26