i06 diamond light source stuart cavill sarnjeet dhesi francesco maccherozzi kevin edmonds
DESCRIPTION
X-ray PhotoEmission Electron Microscopy of domains in GaMnAs. I06 Diamond Light Source Stuart Cavill Sarnjeet Dhesi Francesco Maccherozzi Kevin Edmonds Robin Marshall James Haigh. X-ray PhotoEmission Electron Microscopy. In normal XMCD measurements, the difference in the x-ray - PowerPoint PPT PresentationTRANSCRIPT
I06 Diamond Light Source
Stuart CavillSarnjeet DhesiFrancesco Maccherozzi
Kevin EdmondsRobin MarshallJames Haigh
X-ray PhotoEmission Electron Microscopy of domains in GaMnAs
In normal XMCD measurements, the difference in the x-ray absorption spectra for positive and negatively circular polarised x-rays is measured, and difference in absorption is proportional to the magnetic moment in the direction of the polarisation.
The absorption is measured by secondary process:•Auger emission of electrons, by measuring the drain current.•Fluorescence, by measuring the intensity of light emitted by the sample under illumination with x-rays.
In PEEM, we measure the emitted electrons from the sample by accelerating them away from the sample and focusing the image onto a fluorescent screen.
This gives a measure of the local x-ray absorption.
Can measure in positive and negatively circular polarised light to get local XMCD.
energy
X-ray PhotoEmission Electron Microscopy
e-
-2kV
optics, analyser
fluorescent screen
camera
e-
0V
hν
1. on peak, negative circular
2. off peak, negative circular
3. on peak, positive circular
4. off peak, positive circular
L3
L2
1.
2.
3.
4. energy
X-ray PhotoEmission Electron Microscopy
X-ray PhotoEmission Electron Microscopy
ave 22948-22972
20mm FOVj= 0 (107 on manip)T=-175C
ave 22992-22307 ave 23010-23025
20mm FOVj= 5 (102 on manip)T=-172C
10mm FOVj= 5 (102 on manip)T=-172C
20mm FOVj= 5 (102 on manip)T=-172C ave 23128-23143
OOMMF simulation of domains.
•Initial state is with each element having a random direction of magnetisation.•State is allowed to evolve to minimise energy.•Domains form as different regions have different direction magnetisation.•The domains grow and merge.
LEEM image.
25nm Ga(1-x)MnxAs , x = 0.12
50μm
50 100 150 200 250 300 3506
7
8
9
10
11
12
13
14
300 350 400 4505
5.5
6
6.5
7
7.5
8
8.5
9
9.5
a
ab
b
d
c
dcas
ymm
etry
(%)
asym
met
ry (%
)
-180 -170 -160 -150 -140 -130 -120
0
5
10
15
20
25
30
35120 130 140 150 160 170
0
10
20
30
Asy
mm
etr
y (%
)
T - T1 (thermocouple)
PEEM
T (K)
SQUID
Mag
netisation (emu/cc)
1 2 3 4 5
1
2
3 4
5
Heating above Tc
below TcHeat above Tc Cool below Tc