Bulk and Interface Properties of Bulk and Interface Properties of Multilayer SystemsMultilayer Systems

Edson Passamani Caetano

Universidade Federal do Espírito Santo Physics Departament/Espírito Santo/Vitória/Brazil

530 km

Winter season

Studied problems• Non-collinear magnetic coupling

• Exchange bias effect

Sample preparations• Fe/Mn/Fe trilayers (MBE)

• FeNi/FeMn/FeNi trilayers (Sputtering)

Mössbauer results• Fe/Mn/Fe trilayers• FeNi/FeMn/FeNi trilayers

General Remarks

Introduction• Thin films/Multilayers

• Relevant discorverings in multilayers

Outline

Thin films/Multilayers

If the effusion cells

can be independently controlled

substrate

materials A+B

substrate

material A

substrate

System with one of its dimension in nanometer scale

From especial issue of J3M (1999)~1400

AFM Coupling

GMR

RKKY

Relevant Discoverings in Multilayers

Exchange bias+ Spin-Valves

Studied Systems

Influence of interfacial roughness/alloy on the:

(i) Non-collinear coupling of Fe/Mn/Fe trilayers

(ii) EB effect in FeNi/FeMn/FeNi trilayers

AFM

FM

90o

FM90oAFM

90o

FM

M1 upper Fe

M2 lower Fe

Wegded-sample: Fe(10nm)/Cr(xnm)/Fe(10nm)

Pictures from Grunberg´s group

How do Fe layers interact in the simplest multilayer system?

Fe

Fe

AFM

Yan et al. have found non-collinear coupling in Fe/Mn/Fe (PRB 59 (1999))

Fe (5nm)Mn

Fe(5nm)0.5 nm 0.9 nm 1.4 nm

Sample preparation : MBE (KULeuven)Vacuum during the deposition 6x10-11 mbar

Substrate temperature (Ts) = 50-175 ºC

MgO(001)

4 up to 9 nm – natFe Rate of 0.16 Å/s(lower layer)

57Fe (1nm) deposited in both interfaces with 0.07 Å/s

MgO (001)

Mn (x nm) deposited with 0.04 Å/s

natFe 4 nm

Si – 8 nm

MgO(001)

Ag(100nm)or

• Reflection High Energy Electron Diffraction (RHEED) – [KULeuven]

• Rutherford Back-Scaterring (RBS) – [KULeuven]

•X-ray Diffraction (low and high angles) – [KULeuven]

Structural characterization

• VSM and PPMS – [KULeuven and UFES/Brazil]

• X-ray Magnetic Circular Dicroism (XMCD) – [LNLS/Brazil]

• Ferromagnetic Ressonance (FMR) – [UFG/Brazil]

Magnetic Characterization

Hyperfine Characterization

• Conversion Electron Mössbauer Spectroscopy (CEMS) – [KU Leuven and UFES/Brazil]

Experimental Characterization Methods

57Fe Mössbauer Spectroscopy

+1/2

+3/2

-3/2

-1/2

+1/2-1/2

57Fe nucleus

γ-rays direction Mn

57Fe

MgO(001)

Ideal interface

Interface Bhf

Bhfbulk (natFe layer)

-10 -8 -6 -4 -2 0 2 4 6 8 10

0,5

1,0

Con

tage

m (

u.a.

)

Energia = f(v) (mm/s)

Rel

ativ

e tr

ansm

issi

on (

a.u.

)

V(mm/s)

Transmission mode

MLK 10% 14.4 keV

e-

80% 7.3 keV

90%100% 14.4 keV

Rel

ativ

e em

issi

on

Emission mode

V (mm/s)

MgO/Fe(5nm)/Mn(0.5nm)/Fe(5nm) prepared at different Ts

0.4 nm Fe bulk

0.6 nm Fe bulk 57Fe Mn

Si

MgO(001)

Si

MgO(001)

Field direction

MgO/Ag/(100nm)/Fe(10nm)/Mn(x nm)/Fe(5nm)

x = 1.4 nm

-0.1 0.10

TS=500C

-0.3 0 0.3

M/M

S

x=1.0 nm

0H(T)

Magnetometry: Field Applied // to the Film PlaneMagnetometry: Field Applied // to the Film Plane

0.30-0.3

M/M

s

μoH(T)

x = 1.0 nmET= Eanistopry + EZeeman + Eexchange

2 2( )E C C

C

C C

Coupling energy

exch

MgO/Ag(100nm) substrate (TS = 50o C)

Upper Fe layer

Lower Fe layer

θ=470

θ~900

MgO/Fe(5nm)/Mn(1nm)/Fe(5nm) TS=150oC

MgO/Ag(100nm)/Fe(10nm)/Mn(1nm)/Fe(5nm) TS=50oC

17 % of bulk α-Fe

38% of bulk α-Fe

=47o

=72o

EB effect

2nd problem to be shown

Meiklejohn and BeanJAP 33 (1962) 1328

EB effect - Shifting of the

M(H) curve along field axis

Hc1

Hc2

Heb= [HC1–HC2]/2

Py (30 nm)

Py (10nm)FeMn (15 nm)

WTi (10nm)

WTi (10nm)

Si (100)

Deposition conditions:

Vacuum: 5 x 10-8 TorrArgon working pressure (PW): 2, 5 and 10 mTorr;Applied field during deposition ( 460 Oe)TS: 20 oC

Sample preparation: Sputtering (CBPF)

Py=Ni80Fe20

AFM

FM

FM

Samples: A2, A5 and A10 PW= 2, 5 and 10 mTorr

Interfacial effect/EB system

Heb values reduce with roughness

[Nogués et al., PRB 59 (1999) 6984]

Heb values increase with roughness

[Uyama et al., J. Magn. Soc. Jpn. 21 (1997) 911]

Samples: A2, A5 and A10 PW= 2, 5 and 10 mTorr

X-ray Reflectivity data

0 1 2 3 4 5 6 7 80,010,1

110

1001000

10000100000

1000000

2 (degree)

A2

0,11

10100

100010000

1000001000000

A5

Rel

ativ

e in

tens

ity (

a.u.

)

0,11

10100

100010000

1000001000000

A10

X-ray Reflectivity results

Sample Thickness and roughness (nm) from the fits

A2 Py(30.5)/0.3/FeMn(13.6)/0.7/Py(10.1)

A5 Py(30.6)/0.8/FeMn(13.8)/1.1/Py(10.3)

A10 Py(30.2)/1.0/FeMn(13.1)/2.7/Py(10.1)

Py

Py

FeMnUpper Interface

Lower interface

Si/WTi/Py(30)/FeMn(15)/Py(10)/WTiPW= 2, 5 and 10 mTorr (A2, A5 and A10)

-200 -100 0 100 200-800

-600

-400

-200

0

200

400

600

800

Heb2

M

(e

mu

/cm

3 )

H (Oe)

A2 A10

Heb1

A2 A10

Samples: A2 and A10 PW= 2 and 10 mTorr

Sample Heb1 (Oe) HC1(Oe) Heb2(Oe) HC2(Oe)

A2 41.4 3.1 116.1 8.4

A5 25.7 3.7 101.6 11.2

A10 29.0 5.5 62.4 20

Magnetometry

Si/WTi/Py(30)/FeMn(15)/Py(10)/WTiPW= 2, 5 and 10 mTorr (A2, A5 and

A10)

Heb values decrease while

Hc values increase with roughness

Si/WTi(10)/Py(30)/FeMn(15)/Py(10)/WTi(10)

PW= 2, 5 and 10 mTorr (A2, A5 and A10)

ComponentsHyperfine

parametersSamples

A2 A5 A10

Ni80Fe20 (Py)

Bhf (T) 29 2 29 1 28 2

(mm/s)0.04 0.05

0.05 0.01 -0.02

0.09

A % 44 39 35

FeMn +AFM and/or PM interface

phases

A % 56 57 58

FM interfacialalloy

Bhf (T) - 16.6 0.1 16.2 0.4

(mm/s) - -0.08 0.01-0.06

0.01

A % - 4 7

Hyperfine parameters

“chemical roughness (alloy) ” exceeds the interfacial roughness

Ni80Fe20 52%

Fe50Mn50 48%

Calculated fraction

Proposal model Transversal view

Ni

Fe

Roughness and/or alloy

FM phase at the interface

AFM (FeMn + (NiFe)xMny)

Mn

Fase PMAt the interface

Rich- Fe – phase from the NiFe

(sextet)

NiFe

NiFe

FeMn

Py (30 nm)

Py (10nm)FeMn (15 nm)

WTi (10nm)

WTi (10nm)

Si (100)

• In trilayer systems, the upper interface is usually rougher than the lower one. In addition, the “chemical roughness (alloy)” is in general larger than the interfacial/surface roughness.

• The magnetic coupling angles in Fe/Mn/Fe trilayers are related to their interfacial roughnesses and therefore it is not due to the quasi-helicoidal AFM state of Mn layer in the trilayer.

• Bulk magnetic properties of multilayer systems are intrinsically associated with their interface properties.

General Remarks

• The Py/FeMn/Py trilayers Heb 1/roughness and HC roughness. Theirs values are intrinsically related to the fraction of each Mössbauer component.

Prof. Dr. André Vantomme (KULeuven-Belgium)

Prof. Dr. Elisa Baggio-Saitovitch (CBPF/Brazil)

Prof. Dr. Fernando Pelegrini (IFG/Brazil)

Dr. Bart de Groot (KULeuven-Belgium)

Dr. Bart Croonenborghs (KULeuven-Belgium)

Dr. Valberto Pedruzi Nascimento (CBPF/Brazil)

MSc. Breno Segatto (UFES/Brazil)

MSc. Francisco Almeida (KULeuven-Belgium)

UFES KULeuven IF - UFGCBPF

Sponsors:

Thank you!

NiFe

NiFe

phase FM

H direction during deposition

Spins FM planar

Spins AFM planaresFeMn

Spins non-colinear

x Frustation

phase PM and AFM (FeMn and NiFeMn)

Ni(+)FeMn

PM clusters

Spins AFM planarNiFeMn

x

x

x

Spins FMperpendicular

Magnetic structure model