Abstract-Accessing the fundamentals of magnetotransport in metals with terahertz probes

• Zuanming Jin,
• Alexander Tkach,
• Frederick Casper,
• Victor Spetter,
• Hubert Grimm,
• Andy Thomas,
• Tobias Kampfrath,
• Mischa Bonn,
• Mathias Kläui
• & Dmitry Turchinovich

http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3384.html

Spin-dependent conduction in metals underlies all modern magnetic memory technologies, such as giant magnetoresistance (GMR). The charge current in ferromagnetic transition metals is carried by two non-mixing populations of sp-band Fermi-level electrons: one of majority-spin and one of minority-spin. These electrons experience spin-dependent momentum scattering with localized electrons, which originate from the spin-split d-band. The direct observation of magnetotransport under such fundamental conditions, however, requires magnetotransport measurements on the same timescale as the electron momentum scattering, which takes place in the sub-100 fs regime. Using terahertz electromagnetic probes, we directly observe the magnetotransport in a metallic system under the fundamental conditions, and determine the spin-dependent densities and momentum scattering times of conduction electrons. We show that traditional measurements significantly underestimate the spin asymmetry in electron scattering, a key parameter responsible for effects such as GMR. Furthermore, we demonstrate the possibility of magnetic modulation of terahertz waves, along with heat- and contact-free GMR readout using ultrafast terahertz signals.