Magneto-optical Kerr spectra of gold induced by spin accumulation
V. Ortiz, Sinisa Coh, Richard B. Wilson
Abstract
We report the magneto-optic Kerr effect (MOKE) angle of Au magnetically excited by spin accumulation. We perform time-resolved polar MOKE measurements on Au/Co heterostructures. In our experiment, the ultrafast optical excitation of the Co drives spin accumulation into an adjacent Au layer. The spin accumulation, together with spin-orbit coupling, leads to nonzero terms in the off-diagonal conductivity tensor of Au, which we measure by recording the polarization and ellipticity of light reflected from the Au surface for photon energies between 1.3 and 3.1 eV. In a narrow energy range near the interband transition threshold of Au, the sensitivity to magnetization measured exceeds $1\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{rad}\phantom{\rule{0.28em}{0ex}}\mathrm{per}\phantom{\rule{0.28em}{0ex}}\mathrm{A}/\mathrm{m}$. In the photon energy interval of 0.6--4.4 eV, the maximum value for transition ferromagnetic metals like Ni are $<10\phantom{\rule{0.28em}{0ex}}\mathrm{nrad}\phantom{\rule{0.28em}{0ex}}\mathrm{per}\phantom{\rule{0.28em}{0ex}}\mathrm{A}/\mathrm{m}$, while predicted values for heavy metals like Pt or W are $<13\phantom{\rule{0.28em}{0ex}}\mathrm{nrad}\phantom{\rule{0.28em}{0ex}}\mathrm{per}\phantom{\rule{0.28em}{0ex}}\mathrm{A}/\mathrm{m}$. The exceptional sensitivity of the optical properties of Au to spin magnetic moments make Au an exceptionally sensitive optical magnetometer, with potential applications in the development of optospintronic technologies.