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RESEARCH PRODUCT

Accessing the fundamentals of magnetotransport in metals with terahertz probes

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description

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. Terahertz radiation is used to directly probe magnetotransport in metallic multilayers on the timescale of electron momentum scattering—the fundamental conditions of Nevill Mott’s model of spin-dependent conduction in metals.