Abstract
The magneto-optical Kerr effect (MOKE) has recently been achieved on non-ferromagnetic metals by injecting spin currents. To use the magneto-optical Kerr effect as a quantitative tool, it is crucial to study the relationship between the Kerr rotation angle and the spin accumulation on non-ferromagnets. In this work, I measure a transient magneto-optical Kerr rotation on non-ferromagnetic metals of Cu, Au, and Pt driven by an ultrafast spin current from an adjacent ferromagnetic metal. Through comparing the measured Kerr rotation and the calculated spin accumulation, I determine the conversion ratio between the Kerr rotation and the spin accumulation to be: −4 × 10−9 (real part), −2.5 × 10−8 (real part), and −3 × 10−9 (imaginary part) rad m A−1 for Cu, Au, and Pt, respectively, at a wavelength of 784 nm.
Highlights
The optical detection of the magnetization has been possible since the discovery of the Faraday effect and the magneto-optical Kerr effect (MOKE) [1,2]
A spin current from ferromagnetic metals (FMs) to non-ferromagnetic metals (NMs) creates a spin accumulation on NM, and this spin accumulation in conjunction with the spin–orbit coupling of NM causes a rotation of the polarization of light upon reflection
In order to convert the unit of the Kerr rotation to the unit of magnetization (A m−1 ), the Kerr rotation from the ultrafast demagnetization is divided by the static Kerr rotation of −440 μrad of the full magnetization, multiplied by the saturation magnetization of 6 × 105 A m−1
Summary
The optical detection of the magnetization has been possible since the discovery of the Faraday effect and the magneto-optical Kerr effect (MOKE) [1,2]. The MOKE in particular is extensively used for ferromagnetic metals (FMs) because FMs tend to reflect light at a visible range of wavelength. The physical origin of the MOKE on FM is the net magnetization and spin–orbit coupling of FM [3]. The MOKE on non-ferromagnetic metals (NMs) has previously been studied by inducing a magnetic moment with an external magnetic field [4,5,6,7,8]. A spin current from FM to NM creates a spin accumulation on NM, and this spin accumulation in conjunction with the spin–orbit coupling of NM causes a rotation of the polarization of light upon reflection. The optical detection of the spin accumulation on NM enables the quantitative analysis of the spin transport as well as the spin conversion at a timescale of sub-picoseconds
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