-CoFe 2 O 4 nanocomposite films Magnetic Properties of BaTiO 3 -CoFe 2 O 4 nanocomposite films ::::...

Magnetic Properties of BaTiO3-CoFe-CoFe22OO44 nanocomposite films nanocomposite films

:::: Grupo FCD :::: Centro de Física da :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: Universidade do Minho ::::

Univ. Minho: B.G. Almeida, J.A. Mendes and A.G. Rolo

J. Barbosa

IFIMUP: J.P. Araújo and J.B. Sousa

• Introduction

• Samples Preparation

• Structural Characterization

• Magnetic Characterization

• Conclusions


Introduction• Magnetoelectric materials exhibit a coupling between

their electric and magnetic degrees of freedom


Piezoelectric Phase + Magnetostrictive Phase

•The magnetic properties of these nanostructures depend critically on the phase morphology and internal stress distribution

• Nanostructured composites:

Magnetoelectric response

Elastic interactions

Samples Preparation• The BaTiO3/CoFe2O4 samples were produced by laser

ablation.


Substrates: Si(001)PO2=1 mbar TSub= 600ºCLaser: = 248 nm, fluence of 1.5 J/cm2 , 10 Hz repetition rate

• The ablation targets:

• Deposition Conditions:

CoFe2O4 and BaTiO3 mixed and compressed powders with CoFe2O4 concentrations: 20%, 30%, 40%, 50%, 60% and 70%.

Structural Characterization

30 40 50 60

BaTiO3

(101)(110)

BaTiO3

(102),(201),(210)

(BaTiO3)1-x - (CoFe2O4)x

BaTiO3

(112)(211)

BaT

iO3

(200

)

BaTiO3

(111)

Inte

nsi

ty (

a.u

.)

x=20%

x=30%

x=40%

SS

x=50%

x=70%

2(degrees)

SCoFe2O4

(311) (222)S

X-Ray Diffraction:

Unit Cell BaTiO3 Tetragonal CoFe2O4 Inverse Cubic Spinel


Structural Characterization (cont.)

Grain Size:

0 10 20 30 40 50 60 70 80

20

30

40

50

60

70

80

90

100

BaTiO3

Gra

in S

ize

(nm

)

% CoFe2O4

CoFe2O4

CoFe2O4 average grain size approximately constant with increasing CoFe2O4 concentration (~30nm).

BaTiO3 as the concentration of the CoFe2O4 increase, the grain size of the BaTiO3 phase decreases, from 91.5 nm to 30nm.



Lattice Parameters:


20% 30% 40% 50% 60% 70%

3.80

3.84

3.88

3.92

3.96

4.00

4.04

4.08

4.02

4.08

4.14

4.20

4.26

4.32

4.38

4.44

Bulk value

c axes (Å

)a a

xes

(Å)

%CoFe2O4

Bulk value

CoFe2O4 Lattice Parameter BaTiO3 Lattice Parameteres

CoFe2O4 compressed related to bulk, stress relaxing with increasing CoFe2O4 concentration

BaTiO3 progressively lattice distortion with the increase of CoFe2O4 concentration

20 30 40 50 60 70 80 90 100

8.25

8.30

8.35

8.40

8.45

a CoFe2O4

a Bulk

La

ttic

e p

ara

me

ters

of C

oF

e2O

4 p

ha

se

(Å

)

xCoFe2O4

(%)


Raman Spectroscopy:

CoFe2O4 characteristic modes are present


300 400 500 600 700Raman shift (cm-1)

x=20%

x=30%

x=40%

Ram

an in

tens

ity

(a.u

.)

x=50%

x=60%

x=70%

(BaTiO3)

1-x - (CoFe

2O

4)

x

BaTiO3

CoFe2O

4

Reference powders

20 40 60

480

500

a) O-site CoFe

2O

4

Ram

an s

hift

(cm

-1)

xCoFe

2O

4

(%)

Bulk

20 40 60

700

720

Bulk

b) T-site CoFe

2O

4

Ram

an shift (cm-1)

xCoFe

2O

4

(%)

The blue shift in CoFe2O4 modes with CoFe2O4 concentration results from the lattice strain

Magnetic Characterization


-60 -40 -20 0 20 40 60

-2

-1

0

1

2

x=50%

x=70%

m

(x1

0-3 e

mu)

H (kOe)

T = 10 K

x=20%

x=40%

Magnetic moment increases with increasing cobalt ferrite concentration

Hysteresis Cycles:

Magnetic Characterization (cont.)

The coercivity (Hc) decreases with increasing CoFe2O4 concentration.

20 30 40 50 60 70 800

2

4

6

8

10

T = 300K

T = 10K

(BaTiO3)1-x

- (CoFe2O

4)x

Hc (kO

e)

xCoFe2O4 (%)

for x=100%

Hc of small grains (< 40nm in CoFe2O4) to magnetocristaline anisotropy.Hc of big grains (> 40nm in CoFe2O4) stress.

Hc decrease dueto the relaxation of the stress in big grains

to the increase of small grains agglomeration in bigger polycrystalline clusters


Coercive Field (Hc):

Conclusions•BaTiO3/CoFe2O4 deposited films are polycrystalline and composed by a mixture of tetragonal-BaTiO3 and CoFe2O4 with the inverse cubic spinel structure. The grain sizes are in the range 30nm to 100nm.

•CoFe2O4 phase is under compressive stress that relaxes with increasing cobalt ferrite concentration.

•A decrease of the coercive field with increased CoFe2O4

concentration was observed, due to the relaxation of the stress in the films as well as to the increase of particle agglomeration in bigger polycrystalline clusters with increasing cobalt ferrite concentrations.


End!!!


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