Source: http://aoot.osa.org/ome/abstract.cfm?uri=ome-7-12-4316
Timestamp: 2019-04-25 14:31:43+00:00

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The demand for faster magnetization switching speeds and lower energy consumption has driven the field of spintronics in recent years. The magnetic tunnel junction is the most developed spintronic memory device in which the magnetization of the information storage layer is switched by spin-transfer-torque or spin-orbit torque interactions. Whereas these novel spin-torque interactions exemplify the potential of electron-spin-based devices and memory, the switching speed is limited to the ns regime by the precessional motion of the magnetization. All-optical magnetization switching, based on the inverse Faraday effect, has been shown to be an attractive method for achieving magnetization switching at sub-ps speeds. Successful magnetization reversal in thin films has been demonstrated by using circularly polarized light. However, a method for all-optical switching of on-chip nanomagnets in high density memory modules has not been described. In this work we propose to use plasmonics, with CMOS compatible plasmonic materials, to achieve on-chip magnetization reversal in nanomagnets. Plasmonics allows light to be confined in dimensions much smaller than the diffraction limit of light. This in turn yields higher localized electromagnetic field intensities. In this work, through simulations, we show that by using localized surface plasmon resonances, it is possible to couple light to nanomagnets and achieve significantly higher opto-magnetic field values in comparison to free space light excitation.
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Fig. 1 (a) Schematic of proposed design. The substrate used is MgO. Each nanodisk consists of a plasmonic antenna (yellow), with a thin magnetic layer (purple) with a capping layer (green) on top. (b) Schematic of only a nanomagnet with the capping layer. In both figures, the red circular arrow at the bottom indicates that the illumination is with circularly polarized light and the curly red arrow indicates the direction of incidence.
Fig. 2 (a) Permittivity of Bismuth Iron Garnet (BIG) obtained from ref . (b) Permittivity of GdFeCo obtained from ref . (c) Permittivity of plasmonic TiN on MgO experimentally measured in our laboratory from spectroscopic ellipsometry measurements.
Fig. 3 (a) Comparison of the z-component of the opto-magnetic field intensity along the x-axis of BIG-TiN interface for a 10nm thick BIG layer in the MPS (nanomagnet with TiN resonator) and NPS (only nanomagnet) sample. Illumination is with circularly polarized light of intensity 1mJ/cm2 at 710nm wavelength under normal incidence. (b) Wavelength dependence of the z-component of the opto-magnetic field for the MPS sample (50 nm diameter) at the stack center at the TiN-BIG interface. Inset: Plot of HOM,z over the entire volume of the magnet. (c) Plot of HOM,z along the axis of BIG nanomagnet. (z = 0nm refers to the TiN-BIG interface).
Fig. 4 (a) Electric field components along the x-axis of BIG-TiN interface for a 10nm BIG layer in the MPS sample. (b) Electric field intensity plot along the xy and yz plane for the 10nm BIG-TiN MPS structure under illumination with circularly polarized light of intensity 1mJ/cm2 at 710nm wavelength. Top inset: Schematic of the vertical cross-section of BIG-TiN MPS sample (c) Electric field components along the x-axis of BIG-MgO interface for a 10nm BIG layer in the NPS sample. (d) Electric field intensity plot along the xy and yz plane for the 10nm BIG NPS structure under illumination with circularly polarized light of intensity 1mJ/cm2 at 710nm wavelength. Bottom inset: Schematic of vertical cross-section of BIG-MgO NPS structure.
Fig. 5 (a) Comparison of the z-component of the opto-magnetic field intensity along the x-axis of GdFeCo-Si3N4 interface for a 10nm GdFeCo layer MPS (nanomagnet with TiN resonator) and NPS (only nanomagnet) sample. (b) Electric field intensity plots along the xy(GdFeCo-Si3N4) and yz plane for the MPS(nanomagnet with TiN resonator) sample. (c) Electric field intensity plots along the xy(GdFeCo-Si3N4) and yz plane for the NPS(only nanomagnet) sample. Illumination is with circularly polarized light of intensity 1mJ/cm2 at 710nm wavelength under normal incidence.
Fig. 6 (a) Comparison of opto-magnetic field intensity along the x-axis of BIG-TiN interface for MPS (magnet-plasmon coupled) structure and BIG-MgO interface for NPS(only nanomagnet) structure with 20nm diameter. Inset: Schematic of structures. (b) Electric field intensity plot at TiN–BIG interface for MPS sample. (c) Electric field components along the x-axis of the TiN-BIG interface for MPS sample. (d) Electric Field intensity plot along the y-z plane of the MPS sample. Illumination is with circularly polarized light of intensity 1mJ/cm2 at the resonant wavelength of 710nm.
Fig. 7 (a) Wavelength dependence of the z-component of the opto-magnetic field for a 50nm diameter MPS sample at the stack center at the TiN-BIG interface. Inset: Schematic of the structure. Blue arrows correspond to the wavelengths for which the electric field amplitude of light is plotted in b. (b) Electric field intensity plot along the xy and yz plane for the 10nm BIG-TiN MPS structure under illumination with circularly polarized light of intensity 1mJ/cm2. The wavelength of excitation is shown at the bottom left corner (xy plane refers to the BIG-TiN interface).
Fig. 8 (a) Comparison of the z-component of the opto-magnetic field intensity for a 10nm BIG layer along the x-axis of BIG-TiN interface and lower BIG-Si3N4 interface respectively in the MPS(nanomagnet with TiN resonator) and all dielectric (TiN replaced by Si3N4) sample. Illumination is with circularly polarized light of fluence 1mJ/cm2 at 710nm under normal incidence. Inset: Schematic of the two structures. (b) Electric field intensity color maps for the two structures under illumination with 710 nm circularly polarized light of 1mJ/cm2 fluence (xy plane refers to the BIG-TiN and lower BIG-Si3N4 interface in the top and bottom plots respectively).

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