Direct Phase Probing and Mapping via Spintronic Michelson Interferometry

A spintronic approach is introduced to transform classic Michelson interferometry that probes the electromagnetic phase only. This method utilizes a nonlinear four-wave coherent mixing effect. A previously unknown striking relation between spin dynamics and the relative phase of electromagnetic waves is revealed. Spintronic Michelson interferometry allows direct probing of both the spin-resonance phase and the relative phase of electromagnetic waves via microspintronics. Thereby, it breaks new ground for cross-disciplinary applications with unprecedented capabilities, which we demonstrate via a powerful phase-resolved spin-resonance spectroscopy on magnetic materials and an on-chip technique for phase-resolved near-field microwave imaging.

Figure 1

(a) Michelson interferometry that measures a sinusoidal optical intensity $I$ induced by the modulation of the electromagnetic phase $\Psi$. (b) Spintronic Michelson interferometry that measures a sinusoidal electrical signal $V$ caused by the modulation of the relative electromagnetic phase $\Phi$. The inset shows a micrograph of the microspintronic detector.

Figure 2

The voltage signal measured by modulating the rf phase shifter with the detector connected to (a) both microwave paths and (b) only one microwave path. A striking sinusoidal oscillation is observed in (a). (c) FMR spectra measured at 7 GHz and at different $\Phi$. (d) Calculated FMR spectra by using Eq. (2). Note the line shape changes its symmetry and polarity in $\pi /2$ and $\pi$ cycles of $\Phi$, respectively.

Figure 3

(a) FMR amplitude spectrum measured at 7 GHz and $\Phi =0$. (b) Sinusoidal oscillations of $V$ which show a field dependent phase shift due to the FMR. (c) Directly measured (circles) and fitted (solid curve) FMR phase spectrum at 7 GHz. (d) Phase-amplitude map of FMR measured by the phase-resolved spin-resonance spectroscopy, where curves of (a)–(c) can be obtained via the guiding lines.

Figure 4

(a) Setup for near-field phase imaging of dielectric gratings placed behind a horn antenna. Near-field and far-field phase images obtained by scanning the detector along the $x$ axis at a distance of (b) $z=\lambda /6$ and (c) 1.1 $\lambda$, respectively, behind the gratings. Spatial oscillation of the phase determined at (d) $z=\lambda /6$ and (e) 1.1 $\lambda$.