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Origin of Thickness Dependent Spin Reorientation Transition of B2 Type FeCo Alloy Films

Origin of Thickness Dependent Spin Reorientation Transition of B2 Type FeCo Alloy Films. Dongyoo Kim. Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden. Introduction. Chemical composition : 0.55 ≤ x ≤ 0.65.

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Origin of Thickness Dependent Spin Reorientation Transition of B2 Type FeCo Alloy Films

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  1. Origin of Thickness Dependent Spin Reorientation Transition of B2 Type FeCo Alloy Films DongyooKim Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.

  2. Introduction Chemical composition : 0.55 ≤ x ≤ 0.65 Tetragonal distortion : 1.2 ≤ c/a ≤ 1.25 KU = 700 ~ 800 µeV/atom MS = 2.1 µB/atom

  3. Introduction about 15 MLs SRT at 15 ML

  4. Introduction

  5. To account SRT of FeCo films at 15 ML  We have considered film structures. MCA of bulk FeCo cannot explain SRT of FeCo at 15 ML. We calculated FeCo film with coverage of 6, 8, 10, 12, 14, and 16 ML thickness Purposes Giant MCA Energy Chemical Composition Tetragonal distortion

  6. Calculation Method FLAPW method (Full potential linearized augmented plane wave) <Calculated Systems> Exchange correlation potential : GGA Spherical harmonics (lmax ) : 8 Energy cut-offs : 225 Ry and 13.7 Ry Muffin-tin radius of Fe and Co atoms : 2.2 a.u. Lattice Constant: 2.866 Å (experimental value, [PRB, 64, 132102 (2001)]) K-points: 420 points The optimized atomic structure in vertical direction  Force and total energy minimization procedure.

  7. Structural Features Calculated interlayer distance (in Å) Thick Thin c/a = 1.07

  8. Magnetic Moment Calculated spin magnetic moment (in µB) in MT region.

  9. Magnetization Linearly increasing Ms

  10. MAE in Thin Film Structures Eㅗ EMCA = E//– Eㅗ E// MAE = EMCA - ESh

  11. Magnetic Anisotropy Energy About 15 ML EMCA = Torque method [1] Esh = ½ µ0Ms2 Positive value: Perpendicular MCA EMCA = E//– Eㅗ Negative value: in-plane MCA [1] X. D. Wang, R. Q. Wu, D. S. Wang, A. J. Freeman, Phys, Rev, B 54, 61 (1996)

  12. MCA Energy in Thin Film Structures Eㅗ [J. Hong, et. al, PRL, 92, 147202 (2004)] E// K = KV + 2KS/d KV : Volume contributions KS : Surface contributions d: Film thickness

  13. Magnetic Anisotropy Energy 15 ML Average Esh = ~ 90 ML Kv = 142.42 µeV/atom Ks = 132.61 µeV/atom K = KV + 2KS/d Kv = 67.04 µeV/atom Ks = 594.7 µeV/atom

  14. MCA Energy – FeCo (3ML) [FeCo(3ML) /Pt(7ML)]23

  15. MCA Energy – FeCo (3ML) K = KV + 2KS/d K = KV + 2KS/d Kv = 142.42 µeV/atom Ks = 132.61 µeV/atom Cal: EMCA = 227.82 µeV/atom at FeCo(3ML) Exp: EMCA = (208±14) µeV/atom at FeCo(3ML)

  16. We have investigated the thickness dependent magnetic anisotropy of B2 FeCo Films. FeCo films show perpendicular MCA, but MCA energy rapidly decrease as the film thickness increase. The crossover of shape and MCA energies occurs at approximately 15 ML thickness.  This agrees well with many experimental observations. The competition of shape and MCA energies can nicely account for universal behavior of thickness dependent SRT of FeCo alloy films Summary

  17. Thank You

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