Presentation of Licentiate in Physics Engineering of Francisco Almeida

Magnetic characterization of Fe / 57 FeSi / Fe trilayers Francisco Almeida, student from Faculdade de Ci ê ncias da Universidade de Lisboa ( Erasmus exchange ) EST Á GIO PROFISSIONALIZANTE – LICENCIATURA EM ENGENHARIA F Í SICA ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Overview ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Motivation Interlayer exchange coupling Bilinear antiferromagnetic (  = 180 º ) coupling between two ferromagnetic layers Analogy to Heisenberg type exchange: (Bilinear form Hamiltonian) Energy related to the interlayer exchange coupling:

Motivation Giant Magnetoresistivity ,[object Object],[object Object],[object Object],[object Object],1 Baibich, M.N.; Broto, J.M.; Van Dau, F.N. - “ Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattices ”, Phys. Rev. Lett. 61 , 2472 (1988) 2 Binash, G.; Grunberg, P.; Saurenbach, F. - “ Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange ”, Phys. Rev. B 39 , 4828 (1989) GMR plot from Fert, A.; Grunberg, P.; Barthelemy, A. – “Layered magnetic structures: interlayer exchange coupling and giant magnetoresistance”, J. Mag. M. Mat. 1 , 140 (1995)

Interlayer exchange coupling Phenomenological energy expression 1 Slonczewski, J. C. – “Overview of interlayer exchange theory”; Journal of Magnetism and Magnetic Materials, 150 , 13 (1995) Bilinear (AF) coupling Biquadratic coupling Energy power expansion 1 on

Interlayer exchange coupling The RKKY approximation ,[object Object],[object Object],[object Object],2D decay: 3D (general case) decay:

Interlayer exchange coupling The RKKY approximation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Interlayer exchange coupling Temperature and thickness dependence ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Interlayer exchange coupling Debate on the coupling behaviour of Fe/FeSi trilayers ,[object Object],[object Object],de Vries, J.J.; de Jonge, W.J.M. et al – Phys. Rev. Lett. 78 , 3023 (1997) B ü rgler, D.A.; Gareev, R.R. et al - J. Phys. : Condensed Matter 15 S443 (2003)

Samples grown through Molecular Beam Epitaxy ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Samples grown through Molecular Beam Epitaxy ,[object Object],[object Object],[object Object],[object Object]

Samples grown through Molecular Beam Epitaxy

Vibrating Sample Magnetometry ,[object Object],[object Object],[object Object]

Vibrating Sample Magnetometry Measuring hysterysis curves ,[object Object],[object Object],[object Object],[object Object]

Numerical analysis Simulation through energy minimization ,[object Object],[object Object],[object Object]

Numerical analysis Simulation of biquadratic coupling t 1 t 2 (pinned)

Numerical analysis Simulation of bilinear coupling t 1 t 2 (pinned)

Numerical analysis Automatically fitting the data ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[100] Fe // [110] MgO easy hard

Results Coupling strength ,[object Object],[object Object],[object Object],[object Object],[object Object]

Results Coupling strength – C1208 (14 Å FeSi) ,[object Object],[object Object]

Coupling strength – C1208 (14 Å FeSi)

Coupling strength Loose spins model (Slonczewski et al ) Interlayer coupling mediated through “loose spins” in the spacer

Coupling strength Loose spins model fit to data

C1208 (14 Å FeSi) A strange effect

C1208 (14 Å FeSi) Antiferromagnetic fraction (AFF) ,[object Object]

Thinner samples (C1205 and C1206) Difficulties in finding solutions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Thinner samples (C1205 and C1206) Difficulties in finding solutions

Coupling strength All samples ,[object Object],[object Object],[object Object],[object Object],[object Object]

Coupling strength All samples J 0 = Maximum value (null thickness)  = Coeherence length

Conclusions ,[object Object],[object Object],[object Object],[object Object],[object Object]

References ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Rutherford Backscattering Spectrometry (inacabado…) ,[object Object],[object Object],[object Object],[object Object]

Rutherford Backscattering Spectrometry Stoichiometry of the Fe 1-x Si x spacer layer (inacabado…) ,[object Object],Sample 0° 80° He + Detector

Presentation of Licentiate in Physics Engineering of Francisco Almeida

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Presentation of Licentiate in Physics Engineering of Francisco Almeida