No abstract

Understanding spin-selective interactions between electrons and chiral molecules is critical to elucidating the significance of electron spin in biological processes and to assessing the potential of chiral assemblies for organic spintronics applications. Here, we use fluorescence microscopy to visualize the effects of spin-dependent charge transport in self-assembled monolayers of double-stranded DNA on ferromagnetic substrates. Patterned DNA arrays provide background regions for every measurement to enable quantification of substrate magnetization-dependent fluorescence due to the chiral-induced spin selectivity effect. Fluorescence quenching of photoexcited dye molecules bound within DNA duplexes is dependent upon the rate of charge separation/recombination upon photoexcitation and the efficiency of DNA-mediated charge transfer to the surface. The latter process is modulated using an external magnetic field to switch the magnetization orientation of the underlying ferromagnetic substrates. We discuss our results in the context of the current literature on the chiral-induced spin selectivity effect across various systems.

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for GdFeCo-based materials. The AO-HIS has been described by a thermal-driven switching mechanism attributed to the transient ferromagnetic-like states and the transfer of angular momentum between Gd sub-lattice and FeCo sub-lattice. [2,3,[17][18][19][20] Very recently, this type of switching has not only been observed in the case of light pulses, but also for electron pulses. [7][8][9] In contrast to AO-HIS, in the case of alloptical helicity-dependent switching (AO-HDS), the final state of magnetization is determined by the circular polarization of the light. AO-HDS has been observed for a large variety of magnetic materials such as ferrimagnetic alloy, ferrimagnetic multilayer, ferromagnet thin films, and granular recording media. [4,5,[10][11][12][13][14][15] However, so far, multiple pulses are necessary to fully deterministically switch the magnetization for AO-HDS. [10,16] The use of singlepulse switching would be interesting because it is ultrafast and energy-efficient, however, restriction to Gd-based materials limit potential spintronic devices application. Furthermore, in order to move towards ultrafast-spintronic applications, one needs to study and understand the fundamental mechanism not only for single layers, as it has been done in most study so far, but also in more complex structures like spin-valve structures, a key building block of modern spintronics. Selective magnetization switching in spin-valve structures or more complex heterostructures will enable multi-level magnetic storage and memories. [21][22][23] Here, we demonstrate that the four possible magnetic configurations of a magnetic spin-valve structure ([Co/Pt]/Cu/GdFeCo), shown schematically in Figure 1 where both layers are magnetically decoupled, can be accessed using a sequence of single fs light pulses. We show that a single laser pulse is able to switch the magnetization of either the GdFeCo layer alone or the magnetizations of both GdFeCo and [Co/Pt] layers, depending on the optical pulse intensity. We attribute this magnetic configuration control of the multilayer to, in part, a result of the ultrafast magnetization dynamics in spin-valve structure as well as ultrafast non-local transfer of angular momentum between layers. [24][25][26][27][28][29] Indeed, ultrafast quenching of magnetization in ferromagnetic or ferrimagnetic layers creates spin-polarized currents that propagate in the metallic spacer layer and transfer the angular momentum to the other magnetic layer. We believe the switching of the [Co/Pt] layer results from a combination of optical excitation and the All-optical ultrafast magnetization switching in magnetic material thin film without the assistance of an applied external magnetic field is explored for future ultrafast and energy-efficient magnetic storage and memories. It is shown that femtosecond (fs) light pulses induce magnetization reversal in a large variety of magnetic materials. However, so far, only GdFeCo-based ferrimagnetic thin films exhibit magnetization switching via a single optical pulse. Here,...