Au dependence of the mid infrared optical and magnetorefractive properties of Ni₈₁Fe₁₉/Au GMR multilayers

Abstract

We present an analysis of the optical and magnetorefractive properties of a series of Ni 81 Fe 19 /Au multilayers grown by magnetron sputtering as a function of the Au spacer thickness. The multilayers reach giant magneto resistance values of 4% with low magnetic fields for 2.3 nm Au spacers. The experimental results are well described taking only into account the contribution of the conduction electrons with spin dependent scattering times and different electron concentrations for the two spins. It is shown that the spectral response of the magnetorefractive effect depends strongly on the spin up vs. spin down ratio of both, scattering time and electron concentration. This dependence can be used to optimize mid infrared modulation of optical devices.

Broad band infrared modulation using spintronic-plasmonic metasurfaces

“…The metasurfaces that we consider in this work consist of different arrays of randomly arranged slits (the orientation of the slits is the same for all of them but their position within the array is random) fabricated on 70 nm thick Ni 81 Fe 19 /Au multilayers exhibiting 3.8% GMR [21,28]. We used a random arrangement to avoid diffraction effects intrinsically linked to ordered structures and the excitation of surface plasmon polaritons (propagating plasmons) mediated by the diffraction grating, and therefore to limit the spectral analysis to the localized optical response of the slits.…”

Active photonic platforms for the mid-infrared to the THz regime using spintronic structures

“…Recently, sizeable MRE values at very low magnetic fields (a few tens of Oe) have been reported in the Ni 81 Fe 19 / Au multilayer system [61,63]. In the upper panel of Figure 7A we show schematics of such multilayer, typically deposited on CaF 2 (111) single crystalline substrates with a Ti seed layer.…”

“…They can also be treated as empirical parameters. Obviously, the conductivity of the AP and P states must be related, and different approaches have been proposed to connect them, such as to assume equal electron concentration and masses for both spins and correlate the relaxation times of the AP and P states as: 1/τ AP =(1/2)*(1/τ ↑ +1/τ ↓ ), or to express the conductivities of the AP and P states in terms of the conductivities of the spin up and spin down electrons [13,[59][60][61]. Finally, the differences in the conductivity results in a difference of the optical properties for the two magnetic states of the system.…”

“…The dots correspond to experimental values, the red lines represent a theoretical fit for a multilayer with 0.8% GMR, and the gray dashed lines and black lines represent two theoretical simulations for a multilayer with 4% GMR, (see text). Adapted with permission from ref [61], © The Optical Society. similar, 19.6% (gray dashed lines) and 24.5% (black lines), respectively.…”

“…As mentioned in Section 3.2, Ni 81 Fe 19 /Au multilayers present sizeable MRE values at pretty low magnetic fields, and can be deposited using standard thin film techniques, such as thermal evaporation or sputtering, which allow the required control of the individual Au layers' thickness at the atomic level. For example, 4% GMR is achieved for 2.3 nm Au spacer thickness, while it vanishes for 1.9 and 2.6 nm [61]. Based on Ni 81 Fe 19 /Au multilayers, magnetic field control of the mid IR response in a variety of metastructures has recently been demonstrated, with predicted perspectives of continuous increased modulation for longer wavelengths [100][101][102].…”