FIRB “Microsistemi e Nanomateriali Magnetici”Tematica T4 “Films e Multistrati”

Nanocompositi Magnetici MultistratoLaboratorio “Superfici”

M. Carbucicchio, M. Rateo, M. Prezioso, F. Zini Dipartimento di Fisica – Università di Parma

Steve BennettDepartment of Synchrotron RadiationDaresbury LaboratoryWarrington, UK

Frank J. BerryDepartment of ChemistryThe Open UniversityMilton Keyness, UK

Michel LabruneLaboratoire PMTM-CNRSUniversité Paris-13Villetaneuse, France

Collaborazioni:

G. Asti, M. Ghidini, M. SolziLaboratorio “Magnetometria”Dip. Fisica, Università, Parma

A. Paoluzi, G. TurilliLaboratorio IMEMCNR, Parma

Ultra-High Vacuum Growth by Electron Beams

Vacuum: Starting10-8 Pa Operating 10-6 PaDeposition Rate: 0.5 ÷ 0.8 nm/minSubstrates:Amorphous Quartz

Si(100), Si(111) no native oxide removal

Characterization:

Auger Electron SpectroscopyLayer Thickness, Very Low Contamination

Grazing Incidence X-Ray Diffraction (SRS Daresbury, UK)Crystallographic Structure, Textures, Grain Sizes

Grazing Incidence X-Ray Reflection (SRS Daresbury, UK)Thickness, Density, Interface Roughness

Atomic Force MicroscopyMorphology of Surfaces

Transmission Electron Microscopy (Erlangen, DE)Morphology of Multilayers and Interfaces

Conversion Electron Mössbauer SpectroscopyComposition and Dimensions of InterfacesDirection of Magnetization

Magnetic Force MicroscopyMagnetic Domains

1. Model System

Co/Fe + Co Multilayers Co: 5.0 ÷ 15.0 nmFe 0.5 ÷ 45.0 nm

2. RE-TM Systems

Co/NdFeB/Co + Mo Nd2Fe14B arc evaporated5[SmCo/Fe] + SmCo + Au SmCo5 arc evaporated

3[SmCo/Co] SmCo5 from 10[Sm0.3/Co0.5]Co/SmCo5/Co SmCo5 co-evaporated

Materials:

In-plane AGFM Hysteresis Loops (IMEM)

Interaction-based deviation parameter

MR = saturation remanenceIIRM(H) = isothermal remanenceIDCD(H) = dc demagnetization remanence

M > 0 positive exchange coupling(ferromagnetic interaction)

Model System: simple materials soft/hard ratio = 3

Depth (nm)

0 1 2 3 4 5 6 7 8 9 10 11 12

Co

Con

cent

rati

on %

0

20

40

60

80

100

120

Fe C

once

ntra

tion

%

0

20

40

60

80

100

120

Co CoFe

Pure IronInterfaces

Hhf distribution:- main peak (35 T)

narrow linewidth similar sublattices sharp Fe concentration gradient

- small peak (32 T)broad linewidth a few Fe into Co

Interface Analysis: CEMS

Applied Magnetic Field (Oe)

-100 -50 0 50 100

Mag

neti

zati

on (

emu)

-1e-3

-5e-4

0

5e-4

1e-3

For Fe layer thickness up to 24 nmStrong Uniaxial Magnetic Anisotropy

Hard Axis Low Hysteresis (Mr/Ms 0)Easy Axis High Squareness (Mr/Ms 1)

Remanence ratio Mr/Ms vs the in-plane applied magnetic field angle

180° periodicity with |sin| behaviourAnisotropy constant K1 (1.77 7.63) 104 erg/cm3

Co5nm/Fe2nm

Magnetic Anisotropy

AGFM Hysteresis Loops (IMEM)

Fe layer thickness:< 5 nm in-plane magnetization 5 24 nm out-of-plane ~10° > 24 nm out-of-plane ~40°

Fe layer thickness (nm)

0 5 10 15 20 25 30

out-

of-p

lane

ang

le

(deg

)

0

10

20

30

40

No stray fields Stretched domains Stripe domains

CEMS MFM

First Endeavors: RE-TM Hard Layer

AGFM Hysteresis Loop (IMEM)

Problems: - Uncoupled Phases- Low Coercive Field- Composition

Co/NdFeB/Co

H (Oe)

-100 -80 -60 -40 -20 0 20 40 60 80 100

M (

emu/

g)

-60

-40

-20

0

20

40

60

Single Phase Magnetic Behaviour

AGFM Hysteresis Loop (IMEM)

H (Oe)-1000 -500 0 500 1000

M/M

s

-1.0

-0.5

0.0

0.5

1.05[SmCo/Fe]+SmCo+Au

Problems: - Stoichiometry- Reproducibility- Interdiffusion (GIXRR, CEMS)

CEMS for 5[SmCo/Fe] + SmCo + Au

AGFM Hysteresis Loop (IMEM)

Synchrotron Radiation GIXRD Pattern

Single Phase Magnetic BehaviourLow Coercive Field: NanostructurationSmCo5 Stoichiometry

Co/SmCo5/Co co-evaporated

H (Oe)

-400 -200 0 200 400

M/M

s

-1.0

-0.5

0.0

0.5

1.0

Co/SmCo5/Co co-evaporated

2 Angle (deg)

20 30 40 50 60 70 80 90

Cou

nt r

ate

(cps

)

0

500

1000

1500

2000

Future Activities

TEM and HEED Analyses both in plane and in cross-section

- Morphology, Defectivity - Continuity, Thickness of layers- Grain Sizes, Crystallographic textures - Phase Composition Mapping - Roughness, Interdiffusion, Dimensions of Interfaces

Synchrotron Radiation GIXRD

- Phase Composition - Grain Size, Textures- Kind and Intensities of Stresses- Depth-profiling: different X-ray incidence angles

Ultra-High Vacuum Electron Beam Deposition of

- RE-TM Films with High Coercive Fields- RE-TM/Fe Bilayers and Multilayers

AFM and MFM observations- Morphology - Magnetic Domains

CEMS- Composition and Dimensions of Interfaces- Direction of Magnetization