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Traian PETRISOR Master 2 Internship Internship Coordinator Ursula EBELS

Magnetization dynamics at high frequencies FMR using an inductive method. Traian PETRISOR Master 2 Internship Internship Coordinator Ursula EBELS. Motivation. Importance of magnetization dynamics in new devices:. MRAM, Magnetic Random Access Memories; RF oscillators;.

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Traian PETRISOR Master 2 Internship Internship Coordinator Ursula EBELS

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  1. Magnetization dynamics at high frequencies FMR using an inductive method Traian PETRISOR Master 2 Internship Internship Coordinator Ursula EBELS

  2. Motivation Importance of magnetization dynamics in new devices: • MRAM, Magnetic Random Access Memories; • RF oscillators; • High Frequency Characterization of Materials for the mentioned applications • Replacement of the classical FMR techniques with a broadband measurement; 1

  3. Magnetization Dynamics Heff q M F Equation of motion: precession 2

  4. Magnetization Dynamics Heff q M F Landau-Lifschitz-Gilbert equation: damping precession • precession frequencies are in the GHz range, while relaxation proccesses • are of the order of ns; 3

  5. Ferromagnetic Resonance • uniform oscillation mode; Excitation: External radio frequency magnetic field FMR: 4

  6. The Coplanar Waveguide Critical parameters in determining Z:-central line width; -gap width; -substrate dielectric constant; -line conductivity. 5

  7. What do we measure in a FMR experiment? 6

  8. What do we measure in a FMR experiment? • for the radio frequency field we • have a harmonic behaviour: • for small oscillations, we have • harmonic solutions for mx: • so that: • if we consider 7

  9. Transmission Line Theory TEM(Transverse Electric and Magnetic Fields) mode of propagation Telegrapher’s Equations: • characteristic impedance • V and I are traveling waves having a propagation constant, 8

  10. 9

  11. The Vector Network Analyzer • in order to perform an FMR experiment and obtain c, we have two • basic requirements: • Radio frequency pumping field, hrf ; • Measurement of DZ ; • Solution: use of the Vector Network Analyzer (VNA) 10

  12. The Vector Network Analyzer S21 Transmitted Incident a1 b2 S11 Reflected Reflected S22 b1 a2 S12 Transmitted Incident • at high frequencies it is difficult to measure voltages and currents, • → use of S-parameters • the S-parameters are determined by measuring the incident, reflected • and transmitted power; 11

  13. Using the S-Parameters Localized impedance 12

  14. The Vector Network Analyzer Calibration • in order to make relevant measurements the Network Analyzer has to be • calibrated; • Calibration Process:-determination of the systematic sources of errors • by measuring known standards (SOLT); • - mathematical removal of the errors from subsequent • measurements; • - shifting the reference planes of the measurement; 25ps Delay Line • we find 13

  15. The Studied Samples • pre-existing Coplanar Waveguides with 100nm thick Py lines on top; • the lines were fabricated from Cu/Ta on high resistivity Si substrate; • designed to have a Zc=50W→TEM propagation mode; 900µm Access port Access port • central line width: 5µm; Py line width: 4µm • the lines did not show the expected behavior, non-TEM propagation mode; 14

  16. The Studied Samples • pre-existing Coplanar Waveguides with 100nm thick Py lines on top; • the lines were fabricated from Cu/Ta on high resistivity Si substrate; • designed to have a Zc=50W→TEM propagation mode; 900µm Access port Access port • the lines did not show the expected behavior, non-TEM propagation mode; 15

  17. Measurement Protocol in an FMR Experiment Signal measurement, precession Reference measurement, no precession Substraction of the two contributions 16

  18. Extraction of dynamic susceptibility • the results are not in agreement with the theoretical behaviour; • Reason: we did not take into account propagation effects, we used the localized • impedance model; 17

  19. Extraction of dynamic susceptibility • the results are in agreement with theoretical behaviour; 18

  20. Conclusion • After phase correction the results are in good agreement with expected behaviour. 19

  21. Perspectives 900µm Access port Access port • Improvement of the coplanar waveguides: • - change of geometry; • - oxyde layer between substrate and lines; • Extraction of the dynamic susceptibility using the • equivalent circuit approach; • Removing access port contribution from measurements by performing different calibration • (ex. TRL, LL); • Characterization of different materials and structures. 20

  22. Acknowledgments I would like to express my gratitude towards Ursula EBELS for her constant help and support during the entire period of the internship and to Bernard VIALA and Jean-Philippe MICHEL for their patience and support in preparing this presentation 21

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