Obtaining soft x-ray constants across the 2p edge of Fe in ...

Obtaining soft x-ray constants across the 2p edge of Fe in ...

Obtaining soft x-ray constants across the 2p edge of Fe in thin films by resonant magnetic scattering experiments of polarized soft X-rays Fabian Walter, H.-Ch. Mertins, Andreas Gaupp, Franz Schfers, Wolfgang Gudat Synchrotron Radiation BESSY II Synchrotron radiation as a light source. Radiation is produced by electrons radiating to due centripetal acceleration when following a circular path of about 240m circumference near the speed of light (Peatman) Advantages: Strong bundled light beam Polarization and intensity can be precisely calculated Coherence and time structure High intensity of the light beam Continuous spectrum (Peatman) Undulators Tuneable and known polarisation and intensity Polarisation of emitted light can thus be controlled to have circular and linear components (Weiss, Sahwney)

Undulator Radiation Gap and shift Application Using synchrotron radiation for reflection and transmission measurements Magnetooptical effects Example: Determining optical constants for magnetic materials such as Fe Optical constants are not certainly known for many materials in the VUV Needed for manufacturing of computational devices Knowledge of polarization of the incoming light beam enlarges possibilities Magnetooptical Kerr-Effect (MOKE) L-MOKE P-MOKE T-MOKE B B

2 2 2 B Magnetic Dichroism n 1 i ( ) AL,T RL,T RL,T RL,T RL,T BESSY Soft X-Ray Polarimeter Analyzer

Polarizer 2A h S= (S0,S1,S2,S3) Filter Collimator Io P Detector D A Magazine Frame Holder Multilayer Frame Fit curves for L-Moke 55

B + Intensity (arb. units) 50 45 E=708.75eV data fit 40 L-MOKE 100nm Fe 35 B - 30 0 60 120 180 240

azimuthal angle (deg) 300 360 FWalter sample_fit Magnetic Dichroism n 1 i ( ) AL,T RL,T RL,T RL,T RL,T Fit curves for L-Moke 55 B + Intensity (arb. units)

50 45 E=708.75eV data fit 40 L-MOKE 100nm Fe 35 B - 30 0 60 120 180 240 azimuthal angle (deg) 300 360

FWalter sample_fit Asymetry in L-MOKE 0,40 0,35 L-MOKE asymetry 100nm Fe 0,30 E=707.5 eV E=708.75 eV E=709.25 eV 0,25 0,20 0 60 120 180 240 azimuthal angle (deg) 300

360 FWalter lasymetries Fit curves in T-MOKE 52 50 B Intensity (arb. units) 48 + 46 E=708.75eV data fit 44 42 B - T-MOKE 40 100nm Fe

38 36 34 32 0 60 120 180 240 azimuthal angle (deg) 300 360 FWalter sample_fit Asymetry in T-MOKE 0,35 T-MOKE 0,30 100nm Fe E=707.5 eV E=708.75 eV E=709.25 eV asymetry

0,25 0,20 0,15 0,10 0,05 0,00 0 60 120 180 240 azimuthal angle (deg) 300 360 FWalter tasymetries Results for non-magnetic terms 0,007 0,004 0,003 0,006

100nm Fe 0,005 0,004 0,001 0,003 0,000 0,002 -0,001 0,001 -0,002 0,000 704 706 708 710 712 energy (eV) 714 716

718 FWalter optical_constants 0,002 Results for magnetic terms 0,0016 0,0005 0,0014 100nm Fe 0,0012 0,0000 0,0008 -0,0005 0,0006 0,0004 -0,0010 0,0002 0,0000

-0,0015 704 706 708 710 712 energy (eV) 714 716 718 FWalter optical_constants 0,0010 Comparison with other experiments -3 2,5x10 -3 -2,5x10 Fe(+/-)

0,0 -3 -5,0x10 B+ Bragg (Fe/C) B- Bragg (Fe/C) MOKE (100nm Fe) -3 -7,5x10 -3 6,0x10 -3 5,0x10 -3 4,0x10 -3 3,0x10 -3 2,0x10 -3

1,0x10 -3 B+ Bragg (Fe/C) B- Bragg (Fe/C) MOKE (100nm Fe) Fe(+/-) 7,0x10 0,0 690 700 710 720 energy (eV) 730 740 FWalter bragg Comparison with other experiments -3 1,0x10 -3

2,0x10 0,0 -3 -2,0x10 -3 -1,0x10 Bragg (Fe/C) Faraday (Fe/C) Faraday (50 nmFe) MOKE (100nm Fe) 0,0 -1,0x10 -2,0x10 -3 Bragg (Fe/C) Faraday (Fe/C) Faraday (50nm Fe) KKT of MOKE (100nm Fe) -3

690 700 710 720 energy (eV) 730 740 FWalter bragg Conclusion Exploiting tuneable synchrotron radiation Obtaining optical constants for Fe New technique for obtaining optical constants in the soft x-ray regime for other materials such as Co, Ni, Gd

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