Formation Mechanism of Nano-Oxide Layer on the Surface of Co
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Formation Mechanism of Nano-Oxide Layer on the Surface of Co 2 (CrFe)Si Full Heusler Alloy for nanocontacts CPP-Spin Valves. Y. SHIOKAWA , Y. Saki, S. Kawasaki, M. DOI and M. SAHASHI, Department of Electronic Engineering, TOHOKU UNIIVERSITY. Back ground. Experiment.

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Formation Mechanism of Nano-Oxide Layer on the Surface of Co2(CrFe)Si Full Heusler Alloy for nanocontacts CPP-Spin Valves

Y. SHIOKAWA, Y. Saki, S. Kawasaki, M. DOI and M. SAHASHI, Department of Electronic Engineering, TOHOKU UNIIVERSITY

Back ground

Experiment

Nano-Conatct Magnetoresistance (NCMR)

  • Deposition

  • Ion Beam Sputtering

  • Magnetron Sputtering

  • Surface Analysis

  • RHEED, in-situ STM

  • Magnetic Measurement

  • VSM

  • Other measurement

  • Cross-sectional TEM

  • STEM, HAADF-STEM

Co2FeSi characterstic

(Co:Fe:Si= 49.2 : 28.2 : 22.6 )

A2 structure

  • Co0.9Fe0.1-AlOx NOL [1]

  • MR ratio = 1%, RA = 0.7 Ωμm2

Capping

[1] Y. Shiokawa, et al, Intermag 2008, ES-05, Madrid, Spain, (2008)

[2] H. N. Fuke, et al, IEEETrans. Magn. , 43, (2007) , 2848

IrMn7 nm

AlOx NOL

  • Fe0.5Co0.5-AlOx NOL [2]

  • MR ratio = 11%, RA = 1 Ωμm2

Co0.9Fe0.13 nm

B2: (200)

Natural Oxidation

L21: (110)

A2: (220)

High spin polarization materials

CFS3 nm

  • Need Higher MR ratio for 2Tbit/in2

  • (MR ratio =50 %, RA = 0.3Ωμm2)

  • Full-Heusler alloy

    • Co2FeSi (β≃0.6)

    • Co2Cr0.1Fe0.9Si (β≃0.69)

Cr 5 nm

Ta 30 nm

Cu 285 nm

To clarify the formation mechanism of NOL using high spin polarization material Co2FeSi.

J. Sato, H. Imamura, private communication (unpublished)

Ta 5 nm

SiOx sub.

Pupose

Results

Direct obsevation of NOL by cross-section TEM and XPS

Hin dependence of intensity of Natural Oxidation

NOL B

NOL A

tCr≧0.5nm

NOL has no NC

NOL

1~1.2nm

NOL

1~1.2nm

IrMn

CoFe

CFS

Cr

tCr=0 nm (without Cr)

There are big contacts.

10nm

Ta

NOL A & B

XPS shows NOL is composed of SiO2 and Cr2O3.

HAADF-STEM

STEM

NOL B

tCr=0.1 nm (half ML)

Possibility 1 nm NCs.

NOL A

Schematic formation mechanism of CFS-CrOx NOL

  • NOL has NCs made by SiO2 and Cr2O3.

  • NCs is the shape like illustration.

  • NOL A: thickness 1~1.2 nm without NC.

  • NOL B: HAADF-STEM shows the region is lack of oxygen.

    • ⇒ metal path?

Brightness

Relation between MR ratio and RA

Position (nm)

Calculation method

NOL A

ρNC: 100μΩcm、 tNOL=1nm

RANOL=50Ωμm2、

MRNOL=12%, MRNC=1.5%

Summary

  • Formation mechanism of CFS-CrOx NOL is clarified. The mechanism is:

    • NOL is composed of SiO2 and Cr2O3 mainly.

    • NC is made in the shape to extend to the under CFS layer.

  • This mechanism suggest the MR ratio depends on the under ferromagnetic layer.

H. N. Fuke, M. Sahashi et al , IEEE Trans. Magn.,vol 43.6 (2007).

NOL B

  • NCs has effect of MR(1.5%) by calculate line.

  • MR ratio didn’t depend on the upper ferromagnetic material (CoFe vs FeCo) .

Cr2O3

SiO2

The 2009 Summer School, IEEE Magnetics Society Summer School

2009/9/20~25


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