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 (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 J. Sato, H. Imamura, private communication (unpublished) Ta 5 nm SiOx sub.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