Abstract
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.
Highlights
Following the experimental demonstration of ultrafast demagnetization in 1996 utilizing optical pulses [1], the magnetization switching dynamics in these unprecedented time scales has been extensively investigated both theoretically and experimentally [2]
It is estimated that a laser pulse fluence of 1 mJ/cm2 generates an optomagnetic field of 5.2 T!! In [5], the authors utilize 20nm thick films of GdFeCo and show magnetic domain reversal in sub-picosecond timescales for fluences less than 4.5mJ/cm2. Their results show the formation of multi-domain states as well as helicity-independent switching which implies that there is an upper bound to the maximum light intensity that can be used for all-optical magnetization reversal
First we considered illumination of individual Bi-substituted iron garnet (BIG)-titanium nitride (TiN) magneto-plasmonic stack (MPS) and non-plasmonic stack (NPS) nanodisks separately and studied the electric field distribution characteristic of the plasmon resonance at 710nm wavelength
Summary
Following the experimental demonstration of ultrafast (few hundreds of fs) demagnetization in 1996 utilizing optical pulses [1], the magnetization switching dynamics in these unprecedented time scales has been extensively investigated both theoretically and experimentally [2]. Whereas the full physical understanding underlying the ultrafast magnetization reversal remains incomplete, one plausible mechanism invokes the fact that circularly polarized laser pulses provide an effective magnetic field via the inverse Faraday effect. This opto-magnetic field, HOM, is proportional to [E x E*] (E is the light electric field). In [5], the authors utilize 20nm thick films of GdFeCo and show magnetic domain reversal in sub-picosecond timescales for fluences less than 4.5mJ/cm2 For higher fluences, their results show the formation of multi-domain states as well as helicity-independent switching which implies that there is an upper bound to the maximum light intensity that can be used for all-optical magnetization reversal. The utilization of surface plasmons for all-optical switching proposed in this work, paves the way for on-chip integration of nanoscale photonic and spintronic devices for beyond-CMOS circuitry
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