Evolution of surface state and magnetic coercive field by 3d-band filling in Co_xFe_1-x alloy nano-islands

Chuan-Che Hsu^1*, Hung-Hsiang Yang², Wen-Chin Lin¹, Yukio Hasegawa²

¹Department of Physics, National Taiwan Normal University, Taipei, Taiwan
²Institute for Solid State Physics, University of Tokyo, Chiba, Japan

* Presenter:Chuan-Che Hsu, email:aktanzn@gmail.com

We measured the morphology, surface state and spin contrast of Co_xFe_1-x nano-island with various concentration by Low-temperature spin-polarized scanning tunneling microscopy. Most of the nano-islands are double-layer height ~0.4 nm for pure Co, Fe and Co₅₀Fe₅₀ nano-islands. We also characterized the faulted vs. unfaulted Co islands (ref.1) and the fcc vs. bcc Fe islands. [ref.2]. We investigated the surface state evolution of Co_xFe_1-x nano-islands with variation of alloy composition. The surface states peak of the Co₅₀Fe₅₀ nano-island shifted considerably in various position. The result of shifted-surface state might originate from the structural strain-relaxation in the Co₅₀Fe₅₀ nano-islands; the strain effect-induced shift of the surface d-band in metal has been previously reported (ref.3). Finally, we tried to measure magnetic property of Fe-Co alloy islands by spin-polarized scanning tunneling microscopy (SP-STM). The coercivity of Co₈₀Fe₂₀ nano-island is much smaller than that of pure Co nano-island by ~50%.



Reference:
1. François Varchon et al., Physical Review B 77, 165415 (2008)
2. J. Zhou et al., Nano Letters 9, 3867 (2009)
3. M.-C. Desjonqueres and D. Spanjaard, Concepts inSurface Physics (Springer-Verlag, Berlin, 1993)

Keywords: LT-SP-STM, surface state, magnetic coercive