How do you approach characterizing the spin-orbit torque in materials?

Sample interview questions: How do you approach characterizing the spin-orbit torque in materials?

Sample answer:

1. Sample Preparation:
2. Select materials exhibiting strong spin-orbit coupling, such as transition metal alloys, topological insulators, or certain semiconductors.
3. Prepare high-quality thin films, single crystals, or heterostructures with well-defined interfaces and minimal defects.

4. Employ appropriate growth techniques, such as molecular beam epitaxy, sputtering, or pulsed laser deposition, to ensure precise control over the material’s composition, structure, and thickness.

5. Experimental Techniques:

6. Electrical Transport Measurements: Measure the spin Hall effect or the anomalous Hall effect in thin film samples.
   • Apply a charge current parallel to the material’s surface and measure the transverse voltage generated due to spin accumulation.
   • Vary the temperature, magnetic field, and current density to investigate the dependence of spin-orbit torque on these parameters.
7. Second Harmonic Generation (SHG): Utilize SHG microscopy or spectroscopy to probe the spin-orbit torque at surfaces and interfaces.
   • Irradiate the sample with a femtosecond laser pulse and measure the intensity and polarization of the second harmonic light generated.
   • The SHG signal provides information about the spin polarization and symmetry of the electronic states, allowing for the determination of spin-orbit torque.

8. Spin Pumping: Utilize ferromagnetic resonance (FMR) measurements to study spin pumping from a ferromagnetic layer into an adjacent non-magnetic material.

   • Apply a microwave field to the ferromagnetic layer and measure the FMR linewidth or frequency shift.
   • The spin pumping efficiency, which is related to the spin-orbit torque, can be extracte… Read full answer

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