Back ground

1
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 (CoFeSi 49.2
28.2 22.6 ) A2 structure

• Co0.9Fe0.1-AlOx NOL 1
• MR ratio 1, RA 0.7 Oµm2

1 Y. Shiokawa, et al, Intermag 2008, ES-05,
Madrid, Spain, (2008) 2 H. N. Fuke, et al, IEEE
Trans. Magn. , 43, (2007) , 2848

• Fe0.5Co0.5-AlOx NOL 2
• MR ratio 11, RA 1 Oµm2

B2 (200)
A2 (220)
L21 (110)
High spin polarization materials
Need Higher MR ratio for 2Tbit/in2 (MR ratio 50
, RA 0.3Oµm2 )

• Full-Heusler alloy
• Co2FeSi (ß?0.6)
• Co2Cr0.1Fe0.9Si (ß?0.69)

To clarify the formation mechanism of NOL using
high spin polarization material Co2FeSi.
J. Sato, H. Imamura, private communication
(unpublished)
Results
Direct obsevation of NOL by cross-section TEM and
XPS
Hin dependence of intensity of Natural Oxidation
tCr?0.5nm NOL has no NC
tCr0 nm (without Cr) There are big contacts.
NOL A B XPS shows NOL is composed of SiO2
and Cr2O3.
NOL B
tCr0.1 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 11.2 nm without NC. NOL B
HAADF-STEM shows the region is lack of oxygen.
? metal path?
Relation between MR ratio and RA
Calculation method
NOL A
?NC 100µ?cm? tNOL1nm RANOL50?µm2? MRNOL12,
MRNC1.5
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 didnt depend on the upper ferromagnetic
  material (CoFe vs FeCo) .

2009/9/2025
The 2009 Summer School, IEEE Magnetics Society
Summer School