Neutron scattering studies of magnetic semiconductor thin films and superlattices - PowerPoint PPT Presentation

Loading...

PPT – Neutron scattering studies of magnetic semiconductor thin films and superlattices PowerPoint presentation | free to view - id: 8a5d1-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Neutron scattering studies of magnetic semiconductor thin films and superlattices

Description:

Neutron scattering studies of magnetic semiconductor thin films and ... Polarized neutrons and the in-plane magnetic anisotropy in EuS/PbS & EuS/YbSe. x=1 ... – PowerPoint PPT presentation

Number of Views:55
Avg rating:3.0/5.0
Slides: 48
Provided by: henry48
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Neutron scattering studies of magnetic semiconductor thin films and superlattices


1
Neutron scattering studies of magnetic
semiconductor thin films and superlattices
  • T. M. Giebultowicz1 and Henryk Kepa2,1
  • 1. Dept. of Physics, Oregon State university,
    Corvallis, OR,USA
  • 2. Institute of Experimental Physics, Warsaw
    University, Poland
  • Subtitle
  • Doing neutron scattering in Oregon?

2
(No Transcript)
3
Well, Oregonians still can doneutron scattering,
if they have
  • Generous support for their research projects from
    CNR NIST, and from National Science Foundation
  • Good collaborators and good friends!

4
(No Transcript)
5
Outline
  • magnetic neutron diffraction and interlayer spin
    correlations in all-semiconductor
    antiferromagnetic systems, e.g. EuTe/PbTe
  • Interlayer exchange coupling in ferromagnetic
    EuS/PbS and EuS/YbSe superlattices
  • magnetic domain structure of EuS/PbS, EuS/YbSe
    and Ga(Mn)As/GaAs superlattices studied by
    polarized neutron reflectometry.

6
Magnetic semiconductors - historical remark
MOTHER NATUREmade them almost
exclusivelyantiferromagnetic!
  • When we started our research long time ago, we
    had no other choice
  • than to study
  • Antiferromagnetic / NonmagneticSuperlattices
    (e.g., EuTe/PbTe)

7
AFM Bragg reflection
bulk TN 9.6 K
EuTe 3-?m epilayer
8
(No Transcript)
9
EuTe/PbTe superlattices NIST Center for Neutron
Research NG1reflectometer ? 4.75 ?
10
Advent of semiconductor spintronics
  • End of 1990s successes in the sythesis of new
    epitaxial ferromagnetic semiconductors, most
    notably Ga(Mn)As (Curie T may be as high as 175
    K).
  • Much new excitement about magnetic semiconductors
    and their superlattices. All-semiconductor
    heterostructures are expected to play a crucial
    role in second-generation spintronics devices
    (first-generation metallic systems)

11
New epitaxial systems Theoretically
predicted Curie temperatures for strongly p-type
alloys with 5 Mn.
  • Neutrons can be used for
  • Investigating the new systems (transition
    temps., exchange parameters, etc.)
  • Studying effects of current
  • interest, such as, e.g.,
  • interlayer magnetic coupling
  • or the domain structure in
  • superlattices (not necessarily
  • using new materials intere-sting things can be
    done on old systems, e.g.,EuS.

Year 2000 We find Dr. A. Sipatov from Ukraine,
who grows very interesting EuS/PbS and EuS/YbSe
superlattices!
12
Ferromagnetic EuS/PbS and EuS/YbSe SLs
EuS Heisenberg ferromagnet TC 16.6 K (bulk),
Eg1.5 eV PbS narrow-gap (Eg0.3 eV)
semiconductor (n 1017 cm-3) YbSe wide-gap
(Eg1.6 eV) semiconductor (semiinsulator) all
NaCl-type structure with lattice constants 5.968
? 5.936 ? 5.932 ? (lattice mismatch 0.5)
4-200 ?
30-60 Å
number of repetitions 10-20
(001) a6.29 Å
13
(No Transcript)
14
(No Transcript)
15
Unpolarized neutron reflectivity experiments on
the EuS/PbS system (NG-1 reflectometer, NIST
Center for Neutron Research)
16
Electronic band structure in EuS
17
Interlayer exchange coupling mediated by valence
band electrons
J.Blinowski P.Kacman, Phys. Rev. B 64 (2001)
045302. P.Sankowski P.Kacman, Acta Phys. Polon.
A 103 (2003) 621
18
Alternative explanations...
  • PbS is a narrow-gap material. At low T the
    concentrations of carriers may be still pretty
    high. Perhaps the effect seen in EuS/PbS is a
    carrier-mediated coupling?
  • Crucial test make a EuS/XY system, in which XY
    is a wide-gap semiconductor or an insulator
  • An ideal material, YbSe was found for that
    purpose.

19
Unpolarized neutron reflectivity experiments on
the EuS/YbSe system(NG-1 reflectometer, NIST
Center for Neutron Research)
20
EuS/PbS
EuS/YbSe
21
(No Transcript)
22
(No Transcript)
23
EuS/PbS
EuS/YbSe
24
(No Transcript)
25
Advantages of using polarized neutrons FM
domains in Ga(Mn)As/GaAs superlattices
Here are data from a Ga(Mn)As/GaAs
superlattice (6 of Mn) obtained using an
unpolarized beam
26
Polarized neutron beam experiments the
principles
Atomic spins S and the applied magnetic field H
lie in the x-z reflecting planes. External field
H and the neutron polarization P are parallel to
z-axis
Parallel to H projections of S ? non-spin-flip
(NSF) scattering (nuclear-magnetic
interference) Perpendicular ones ? purely
magnetic spin-flip (SF)
27
(No Transcript)
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
Polarized neutron reflectivity profiles for
the EuS/YbSe (46/20) Å. in-plane 110 axis
horizontal
EuS/PbS (30/4) Å - polarization analysis of the
1-st AFM SL Bragg peak
34
Polarized neutrons and the in-plane magnetic
anisotropy in EuS/PbS EuS/YbSe
x1
x1
35
EuS/PbS superlattices on (111)BaF2
  • Polarized neutron reflectivity studies

36
Unpolarized neutron reflectivity measurements
37
Unpolarized neutron reflectivity measurements
38
Unpolarized neutron reflectivity measurements
39
The first SL-peak for different sample rotation
angles
40
The model
. etc., where
and
is the angle of rotation of the sample about Q
41
(No Transcript)
42
Different flipping ratios vs. angle of rotation
of the sample about Q
43
(No Transcript)
44
(No Transcript)
45
CONCLUSIONS
  • Neutron reflectometry offers insight into some
    properties of magnetic semiconductor
    superlattices that cannot be obtained by other
    techniqes (interlayer coupling, domain
    structure)
  • Although the experiments, essentially, offer
    support for the model of intelayer coupling
    conveyed by the valence electrons, they also
    reveal that some ingredients may still be
    missing in that theory
  • In all investigated systems, polarization
    analysis reveals a significant asymmetry in the
    population of domain states - the reasons are not
    yet clearly understood, but this phenomenon may
    have important practical implications and
    studying it is certainly worth pursuing.

46
Neutron polarization analysis
47
For saturated sample a90º
Calculated ratio
Experimental value
About PowerShow.com