properties of ferromagnetic layers grown on semiconductor …...properties of ferromagnetic layers...

Properties of ferromagnetic layers grown on semiconductor by electrodeposition

C. Scheck, P. Evans, R. Schad and G. Zangari

University of AlabamaCenter for Materials for Information Technology, Box870209

Tuscaloosa, AL 35487, USA

Research supported by NSF-ECS-0070236. Made use ofNSF MRSEC Shared Facilities grant DMR-98-09423

Fall review MINT, 18 Nov. 2002Center For Materials For Information Technology

An NSF Materials Research Science and Engineering Center

Motivation• Integration of ferromagnetic films with semiconductors⇒ implementation of novel devices based on spin-

dependent transport (spin transistor, MRAM)

• ECD is a particularly suitable process:• low energy → avoid interdiffusion, clean interface• high quality, epitaxial films can be produced

• Objective: understand and control growth and magnetic properties of magnetic films on GaAs(structure, intermixing, Hc, anisotropy, electric properties)

Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering Center

ExperimentalGrowth

• Substrate: n-GaAs (011)/(001)• 1017 cm-3 Te doped• Back contact: Ga/In eutectic• EG&G 273A Galvanostat• Room Temperature• Graphite counter electrode

Galvanostat

Characterization• Structural: XRD (θ, φ), NMR,TEM• Magnetic: VSM, Torque• Electrical: 4-point probe• Thickness: XRR, XPS

Electrolyte: sulfate solution 0.1 M, pH 2.5Center For Materials For Information Technology

An NSF Materials Research Science and Engineering Center

Thickness calibration


0 50 100 150 2000

40

80

120 ~45% current efficiency

Thic

knes

s (n

m)

Deposition Time (Sec)

1° 2° 3° 4°

102

103

104

105

106 50 seconds 3.5mAcm2 GaAs (001)

Inte

nsity

(CPS

(log

10))

2θ

• X-ray reflectivity carried out on center part of large sample

• XRD measures Ni film + oxide layer

Interface properties: XPS analysis (2)

-865 -860 -855 -850

0

100

200

pure Nioxidizedfilm

∆EDifference

Ni 2p

Inte

nsity

(Cou

nts

X 1k

)

Binding energy (eV)

∆E=3.2eV corresponds to Ni(OH)2

Oxide thickness Ni(OH)2 = 1.9nm

Shift in energy NiO = 1.4eV,Ni(OH)2 = 3.2eV

Center for Materials for Information Technology

A NSF Materials Research Science and Engineering Center

Interface properties: XPS analysis (3)

X-rays

X-rays

-50 -45 -40 -35 -30 -25 -2050

100

150

200

250

300

350

6 nm 0°

6 nm 40°

14 nm 0°

As 3d

Inte

nsity

(Cou

nts)

Binding energy (eV)

-1170 -1140 -1110

5200

5400

5600

5800

6000

6200

6400 Ga 2p6nm 0°

Inte

nsity

(Cou

nts)

Binding energy (eV)

No Ga, As at the surfaceNo or little diffusion at interface

mfp @ 1444eV(As 3d) in Ni = 1.9nm

mfp @ 370eV(Ga 2p) in Ni = 0.75nm

Center for Materials for Information Technology

A NSF Materials Research Science and Engineering Center

Electrical and magnetic measurements

No or little intermixing at the interface

Fuchs model:ρ(T) = ρ∝ + (3/8) (1-p)(ρ∝ × l∝ ) / T

with the bulk resistivity ρ∝ , the bulk mean free path l∝ , the “reflectivity” coefficient p0 20 40 60 80 100 120

0

400

800

1200

16000

200

400

600

(a)

0 10 20 300

250

500

ρ *T

(µΩ

.cm

.nm

)

Ni layer Thickness (nm)

(b)

MS (

emu/

cc) Bulk Ni : Ms=484 emu/cc


Ni-Crystalline Structure (XRD):Out of plane In plane

30° 40° 50° 60° 70° 80° 90°

100

200

300

40° 45° 50°

100

200

300

GaAs (220)

Ni (111)

GaAs (220)

Ni (111) θ offset by 0.5°

Inte

nsity

(Cou

nts)

2θ

-180° -90° 0° 90° 180°

220

200

111

NiGaAs[110]GaAs[100]

Inte

nsity

(Cou

nts)

Φ

Epitaxial relationship Ni(111)[110] // GaAs(011)[110]


Co-Crystalline Structure (XRD) (1):


30° 40° 50° 60°

100

200

300

400

500

hcp-Co 100 hcp-Co 101

GaAs (220)θ offset 0.3°

Inte

nsity

(Cou

nts)

2θ

-180° -90° 0° 90° 180°

5

10

15

20

25

30

35

40

45

50

55

44.16° 280nm

Inte

nsity

(Cou

nts)

Φ

Co fcc (111) or hcp(002)

Hexagonal (hcp) or cubic (fcc) ???

Out of plane In plane

-180° -90° 0° 90° 180°0

5

10

15

20

2575.6° 280nm

Coun

tsΦ

Co fcc (220) or hcp (110)

Co-Crystalline Structure (XRD) (2):

mixture of fcc and hcp phases confirmed by NMR

TEM

190 200 210 220 230 240

0

20

40

60

80

FCC HCP

Co-GaAs [011]30 nm3.5ma/cm

2 60 secs

Spin

-Ech

o In

tens

ity (a

.u.)

frequency (MHz)

NMR

FeNi: both perpendicular and in-plane XRD scan do not show any clear peaks besides GaAs (011).


Magnetic Properties (1)

-180° -90° 0° 90° 180°0.0

0.5

1.00.0

0.5

1.00.0

0.5

1.0

GaAs[110]

GaAs[100]

21nm

Applied Field Angle

25nm

18nm

0 20 40 60 80 100 1200.0

0.5

1.00.0

0.5

1.00.0

0.5

1.0

Ni Thickness (nm)

Co

e.a h.a

FeNi

-1000 0 1000

-1

0

1

-1

0

1

-1

0

1

21nm

[110]GaAs [100]GaAs

Applied Field (Oe)

[110]GaAs [100]GaAs

25nm

Norm

aliz

ed M

agne

tizat

ion

[110]GaAs [100]GaAs

18nm

Uniaxial anisotropy e.a [001]GaAs for Ni e.a [011]GaAs for Co and FeNi

Hysterisis Remanence Squareness


Magnetic Properties (2)

0 50 100 150 200 250 3000

100

200

300

400

500 Easy Ni Hard Ni Easy Co Hard Co Easy FeNi Hard FeNi

H c(O

e)

Thickness (nm)-20 -10 0 10 20 30 40 50 60 70 80

0

200

400

600

800

1000

FeNi

Co

Ni

H k(O

e)

Thickness

•Co films keep its anisotropy even for large thicknesses (>250nm) and so does Ni (up to 90nm for the range studied).

•Ni film exhibit a larger HK value (950 Oe) than anisotropy normal to crystalline anisotropy, which would be ascribed to stress


Conclusions•No or little intermixing at the interface

•Epitaxial relationship for Ni Ni(111)[110] // GaAs(011)[110]

•Mixed structure fcc/hcp for Co but no clear peaks for FeNi

•Uniaxial anisotropy e.a [001]GaAs for Ni e.a [011] GaAs for Co, FeNi

•Future work:•Investigation of the Shottky barrier properties•Spin injection from Ferromagnetic contacts into semiconductor


properties of ferromagnetic layers grown on semiconductor …...properties of ferromagnetic layers...

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