•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

’