Ab initio theory for femtosecond spin dynamics, angle-resolved fidelity analysis, and the magneto-optical Kerr effect in the Ni3(CH3OH) and Co3+(CH3OH) clusters

Theoretical study of electronic structures, magnetic properties, and ultrafast spin manipulation in transition metal adsorbed polycyclic-aromatic-hydrocarbon molecules

We present a first-principles study of the structural, electronic, and magnetic properties of TM(PAH)0/+ (TM = Fe, Co, Ni; PAH = C10H8, C16H10, C24H12, C32H14) complexes and explore the laser-induced spin dynamics as well as their stability with respect to various laser parameters. For each complex, the most stable configuration shows that the TM atom prefers to adsorb at the hollow site of the carbon ring with a slight deviation from the center. The electronic structure and spin localization of the complexes are found to be largely affected by the TM type. Driven by various laser pulses, spin-crossover scenarios are achieved in all structures, while spin-transfer between TM and PAH is achieved in Ni(C10H8), Ni(C16H10), and Ni(C24H12). The influence of the laser energy and chirp on the dynamics is also investigated, providing important information regarding the stability and sensitivity of the dynamical process. All results are believed to reveal the physics nature of the TM-PAH systems, to guide the experimental realization of their ultrafast spin dynamics and thus to promote their applications in future spintronics.

Investigation of the exact spin channels in laser-induced spin dynamics in two mononuclear Cu(II) complexes

In the quest to harness the potential of nanospintronic applications, we analyze and investigate the spin channels for the ultrafast spin dynamics in mononuclear Cu2+(tdp)Cl2 (Cutdp) and Cu2+(tdp)Cl2·MeCN (Cutdp·MeCN) using a high-level ab initio many-body theory. In that spirit, we select two slightly different polymerizations arising from one parent complex. We establish the difference in magnetic behavior between the two complexes which arises solely from the geometrical differences. We calculate the static magnetic properties, such as the magnetic anisotropy of the complexes, which is analyzed by means of the magnetic moment of the ground state. The asymmetry of the core Cu-Cl-Cu-Cl axial plane unit is also reflected in the ground state absorption spectra of the two complexes. Comparisons with the experimental data are in good agreement with the exception of one peak in the theoretical calculations for each of the complexes, confirming the reliability of theoretical methods employed. A major finding in this work is the distinction between classical and coherent superpositions of Λ processes. We employ the selective blocking and retention (SBR) technique to find the unique path or paths for spin dynamic scenarios like spin flip and spin transfer. Additionally, we also present two different scenarios in which intermediate states are involved in spin dynamic processes, (i) classical superposition of Λ processes (i.e., there are many unique paths for transition, even with just one intermediate state the transition completes successfully), and (ii) collective coherent superposition of Λ processes (i.e., there is only one path for the transition, which requires more than one intermediate state to be in a specific coherent superposition). As a consequence, we gain insight into the type of correlations (static or dynamic) involved in a particular spin dynamic scenario.

Using single and double laser pulses on the molecular Ni4@C48H36 system to design integrated nanospintronic units

The accomplishment of long-distance spin transfer scenarios between several magnetic centers is a big challenge for building and supporting spin-logic units for developing future all-optical magnetic unit operations. Using high-level quantum chemistry theory CCSD and EOM-CCSD, we systematically study the ultrafast laser-induced spin-dynamics process on a carbon-based material, to which four magnetic centers are attached. We show that the CCSD method with the 6-31G basis set calculation is sensitive to the C-Ni bond length. The spin density distribution, which is computed using EOM-CCSD with LanL2DZ+ECP calculations, Mulliken population analysis, including spin-orbit-coupling (SOC) and a magnetic field, fulfills the requirements for achieving spin dynamics processes. Different local spin-flip and spin-transfer processes are accomplished within the subpicosecond regime. The impact of the propagation direction of the laser pulse by switching their polar and the azimuthal angles in spherical coordinates on the spin dynamics processes is analyzed. Double laser pulses with time delay δt ≥ 200 × FWHM yield in a realistic magnetic field gradient selectively a lateral resolution, which corresponds to distances smaller than the CMOS scale (2 nm in 2024) while our system size is comparable to the CMOS scale. Here Λ and V processes with two quasi-degenerate intermediate levels are used. We propose a model of an integrated spin-logic processor created from an array of individual spin-logic blocks, which are realized by four magnetic centers Ni. The findings of this study demonstrate the enormous potential of using laser-induced spin dynamics as the fundamental mechanism for future molecular magnetic technology.

Laser-induced ultrafast spin-transfer processes in non-linear zigzag carbon chain systems

We combine the high-level quantum chemistry theory CCSD and EOM-CCSD together with local and global Λ processes to investigate the details of the laser-induced ultrafast spin manipulation scenarios in non-linear zigzag carbon chain systems Ni2@C32H32 and Ni2@C36H36. The spin density distribution, which is calculated on each many-body state using a Mulliken population analysis, fulfills the requirements to accomplish the spin dynamics processes. Various spin-flip and spin-transfer scenarios are accomplished. All the spin-dynamics processes can be achieved within subpicosecond times. Under the influence of a magnetic field, we find that the spin-transfer scenarios are preserved, while the local spin-flip scenario on a Ni atom can be significantly inhibited depending on the strength of the magnetic field. The impact of the propagation direction of the laser pulse on the spin dynamics processes by varying their polar and azimuthal angles in spherical coordinates is investigated. Additionally, we find that double laser pulses successfully induce the spin-transfer processes. Our outcomes underline the significant potential of carbon chain systems as building blocks for developing future all-optical integrated logic processing units.

Long-Distance Ultrafast Spin Transfer over a Zigzag Carbon Chain Structure

Using high-level ab initio quantum theory we suggest an optically induced subpicosecond spin-transfer scenario over 4.428 nm, a distance which is directly comparable to the actual CMOS scale. The spin-density transfer takes place between two Ni atoms and over a 40-atom-long zigzag carbon chain. The suitable combination of the local symmetries of the participating carbon atoms and the global symmetry of the whole molecule gives rise to what we term the dynamical Goodenough-Kanamori rules, allowing the long-range coupling of the two Ni atoms. We also present local spin-flip scenarios, and compare spin flip and spin transfer with respect to their sensitivity against an external static magnetic gradient. Finally, we use two identical laser pulses, rather than a single one, which allows us to accurately control local (intrasite) vs global (intersite) processes, and we thus solve the problem of embedding individually addressable molecular nanologic elements in an integrated nanospintronic circuit. Our results underline the great potential of carbon chain systems as building and supporting blocks for designing future all-optical magnetic processing units.

Reversible ultrafast spin switching on Ni@B80endohedral fullerene

We demonstrate ultrafast (∼100 fs) and reversible spin switching on the endohedral fullerene Ni@B₈₀viaΛ processes.