•Correlation between structure and magnetism in thin films
INFM, Unità di Genova
Francesco Bisio
Experimental techniques:
Magnetism+ structure in situ
MOKE + MSHG,Polar+longitudinal
QLEED
UHV chamber:p~1.5·10-10 mbar;Electromagnet ~800 Oe;MOKE: 670 nm laser diode;SHG: Ti:sapphire 720÷880 nm, <100fs pulse.
viewport
sample
Phosphor-screen
Magnet
Magnet
LEED
Laser 670 nm
viewport
polarizer
polarizer
Mon
och
r.PM
T
Kerr
sig
nal [a
. u
.]
3000200010000time [s]
sampleMagnet
Magnet
Magnetism + Structure: Fe/Cu3Au
Kerr
sig
nal (a
.u.)
4000300020001000time(s)
T=185 K
SROOnset of
Magnetic order
PO
LA
R
Magnet
sample
Magnet
LO
NG
ITU
DIN
AL SRO
T=290 K
sampleMagnet Magnet
LEED
LEED
43210 k||
LE
ED
inte
nsi
ty [
a.
u.]
(00)
(11)
Fe/Cu3Au thin films
•Fcc substrate, a=3.745 Å
•Possibility of stabilising metastable Fe structures
•Possible coexistence of different structural phases within the same film
AF
NMFM
P. M. Marcus et al. PRB 60, 369 (1999)
Rws (a. u.)
Fcc Fe:
Magnetic properties
depend upon lattice
parameter
(110)
(100)
(-110)
a=2.65 Å
c/a=2Au
CuFe
10
8
6
4
2
0x1
03
2.001.95 1.90 1.80
'
30 Å
25 Å
21 Å
17 Å
11 Å
Fe / Cu3Au: structural properties
Inte
nsity
[a.
u.]
Bcc Fe R45°
H [r. l. u.]
Substrate,Pseudomorphic Fe
F. Bruno et al. PRB 66, 045402
GIXRD radial scans vs. film thickness
Structure and morphology
~150 Å
thk >30 Å
Low coverage: thk<10 Å
Medium coverage: 10 Å<thk< 20 Å
High coverage: thk>25 Å
Fe
substrate
Fe
substrate
’ Fe
Fe
substrate
’ Fe
Fe
Structure-magnetism correlationKerr
Asy
mm
etr
y (
arb
. U
n.)
302520151050
Thickness (Å)
Cu3Au
Cu3Au
’
Cu3Au
’
Tdep~295 KHext=± 50 OeHext|| (100)
MM
M
Optical – Magneto Optical response ?Interface hybridization ?Different per atom ?
25
20
15
10
5
0
Coerciv
e fi
eld
[Oe]
6050403020100
Thickness [Å]
Kerr
asy
mm
etr
y [
Arb
. U
n.]
Morphology-magnetism correlation
20
15
10
5
0
Coerciv
e Fie
ld [O
e]
403020100
Thickness [Å]
Kerr
Asy
mm
etr
y [
a. u
.]
Tdep~295 KHext=± 50 OeHext|| (100)
Tdep~295 KHext=± 50 OeHext|| (110)
-40 -20 0 20 40
H (Oe)
35 Å 45 Å
Morphology-magnetism correlation
-40 -20 0 20 40
H (Oe)
40 Å
Hext|| (100)
Kerr
Sig
nal [a
. u
.]
40200-20-40
H (Oe)
9 Å 15 Å 20 Å 25 Å 30 Å
Kerr
Sig
nal [a
. u.]
-40 -20 0 20 40
H (Oe)
10 Å 21 Å 31 Å
Hext|| (110)
10x10-3
8
6
4
2
0
Kerr
Asy
mm
etr
y [
a.
u.]
302520151050
Thickness (Å)
Tdep=345 K Tdep=295 K
Temperature dependence of magnetic properties
Morphological effect
Intermixing + Curie temperature
shift
Kerr asymmetry during growth vs. substrate temperature
People
Università di Genova e UdR INFM
G. Gonella
R. Moroni
S. Terreni
M. Canepa
L. Mattera
Conclusions
Experimental apparatus devoted to the study of structure-magnetism correlation;
Application to heteroepitaxial ultrathin magnetic films;
Study of buried interface properties (MSHG);
Dependence of magnetism upon crystallographic
parameters;
Kerr
sig
nal [a
. u
.]
3000200010000time [s]
sampleMagnet
Magnet
LEED
Experimental techniques: real time MOKE
Kerr
sig
nal (a
.u.)
4000300020001000time(s)
T=185 K
SRO
Onset ofMagnetic order
POLAR Fe/Cu3Au
sample
Magnet
Magnet
LEED
LONGITUDINAL
SRO
T=290 K
Fe/Cu3Au
20x103
15
10
5
0
Inte
nsity
(ar
b. u
nits
)
2.001.951.901.851.80
H (r.l.u.)
~ 2.4 nm
~ 2.1 nm
~ 1.8 nm Fe
~ 2.9 nm
~ 3.7 nm
in= 1.8 deg.
in= 0.8
40
35
30
25
20
15
Spe
ssor
e (Å
)
2.001.951.901.851.80
H (r.l.u.)
in= 0.8 in= 1.8 deg.
fctbct
Inte
nsity
[a.
u.]
H [r. l. u.]
Fe/Cu3Au: structural properties
Coexistence of multiple structural phases on the film
In-depth scan of the film
’
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