Magneto measurements

Nature Phys. http://doi.org/6q3 (2015)

Traditional measurement technology cannot unambiguously quantify the fundamental parameters of the magnetotransport of electrons (the spin-dependent density and momentum scattering time of conducting electrons at the Fermi level) because of the need to make assumptions. Now, Zuanming Jin and co-workers from Germany and Portugal have discovered that ultrafast terahertz spectroscopy can perform the task. Single-cycle terahertz pulses were sent to a sample featuring alternating layers of NiCoFe and Cu and the transmission was measured in the time domain under the external magnetic field. The key to success is that ultrafast terahertz spectroscopy is a contact-free conductivity sampling method that suppresses spin accumulation at interfaces and contacts, preserving the native spin structure of the sample during the measurement. The electron momentum scattering times for majority- and minority-spin were determined to be 57 fs and 19 fs, respectively. The corresponding values for sheet densities were 1.35 × 10²⁰ m⁻² and 1.36 × 10²⁰ m⁻², respectively. Importantly, further analysis revealed that the spin-asymmetry parameters for electron scattering — a key parameter for the giant magnetoresistance effect — was 3.00 at 300 K, which was much larger than expected from traditional measurements.