Antiparallel System Research Articles

Ultrafast Laser Control of Antiferromagnetic-Ferrimagnetic Switching in Two-Dimensional Ferromagnetic Semiconductor Heterostructures.

Realizing ultrafast control of magnetization switching is of crucial importance for information processing and recording technology. Here, we explore the laser-induced spin electron excitation and relaxation dynamics processes of CrCl3/CrBr3 heterostructures with antiparallel (AP) and parallel (P) systems. Although an ultrafast demagnetization of CrCl3 and CrBr3 layers occurs in both AP and P systems, the overall magnetic order of the heterostructure remains unchanged due to the laser-induced equivalent interlayer spin electron excitation. More crucially, the interlayer magnetic order switches from antiferromagnetic (AFM) to ferrimagnetic (FiM) in the AP system once the laser pulse disappears. The microscopic mechanism underpinning this magnetization switching is dominated by the asymmetrical interlayer charge transfer combined with a spin-flip, which breaks the interlayer AFM symmetry and ultimately results in an inequivalent shift in the moment between two FM layers. Our study opens up a new idea for ultrafast laser control of magnetization switching in two-dimensional opto-spintronic devices.

Weak Supramolecular Interactions Governing Parallel and Antiparallel DNA Quadruplexes: Insights from Large-Scale Quantum Mechanics Analysis of Experimentally Derived Models.

The topology and energetics of guanine (G) quadruplexes is governed by supramolecular interactions within their strands. In this work, an extensive quantum mechanical (QM) study has been performed to analyze supramolecular interactions that shape the stems of (4+0) parallel (P) and (2+2) antiparallel (AP) quadruplex systems. The large-scale (≈400 atoms) models of P and AP were constructed from high-quality experimental structures. The results provide evidence that each of the P and AP structures is shaped by a distinct network of supramolecular interactions. Analysis of electron topological characteristics of hydrogen bonds in P and AP systems indicates that the P model benefits from stronger intratetrad hydrogen bonding. For intertetrad stacking interactions, both noncovalent interaction plot and energy decomposition analysis approaches suggest that the stem of the P quadruplex benefits more from stacking than that of the AP stem; the difference in energetic stabilization for the two topologies is about 10 %. Stronger hydrogen-bonding and stacking interactions in the stem of the P quadruplex, relative to those in the AP system, can be an important indicator to explain the experimental observations that guanine-rich oligonucleotides tend to form all-parallel stems with an all-anti orientation of nucleobases. However, in addition to intrinsic stabilization, partial desolvation effects, which affect the energetics and dynamics of the G-quadruplex folding process, call for further investigations.

Conductance spectra of asymmetric ferromagnet/ferromagnet/ferromagnet junctions

A theory of tunneling spectroscopy of ferromagnet/ferromagnet/ferromagnet junctions was studied. We applied a delta-functional approximation for the interface scattering properties under a one-dimensional system of a free electron approach. The reflection and transmission probabilities were calculated in the ballistic regime, and the conductance spectra were then calculated using the Landauer formulation. The magnetization directions were set to be either parallel (P) or anti-parallel (AP) alignments, for comparison. We found that the conductance spectra was suppressed when increasing the interfacial scattering at the interfaces. Moreover, the electron could exhibit direct transmission when the thickness was rather thin. Thus, there was no oscillation in this case. However, in the case of a thick layer the conductance spectra oscillated, and this oscillation was most prominent when the middle layer thickness increased. In the case of direct transmission, the conductance spectra of P and AP systems were definitely suppressed with increased exchange energy of the middle ferromagnet. This also refers to an increase in the magnetoresistance of the junction. In the case of oscillatory behavior, the positions of the resonance peaks were changed as the exchange energy was changed.

BIMODALITY OF CIRCUMSTELLAR DISK EVOLUTION INDUCED BY THE HALL CURRENT

The formation process of circumstellar disks is still controversial because of the interplay of complex physical processes that occurs during the gravitational collapse of prestellar cores. In this study, we investigate the effect of the Hall current term on the formation of the circumstellar disk using three- dimensional simulations. In our simulations, all non-ideal effects as well as the radiation transfer are considered. The size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or anti- parallel. In the former case, only a very small disk (< 1 AU) is formed. On the other hand, in the latter case, a massive and large (> 20 AU) disk is formed in the early phase of protostar formation. Since the parallel and anti-parallel properties do not readily change, we expect that the parallel and anti-parallel properties are also important in the subsequent disk evolution and the difference between the two cases is maintained or enhanced. This result suggests that the disk size distribution of the Class 0 young stellar objects is bimodal. Thus, the disk evolution can be categorized into two cases and we may call the parallel and anti-parallel systems as Ortho-disk and Para-disk, respectively. We also show that the anti-rotating envelopes against the disk-rotation appear with a size of 200 AU. We predict that the anti-rotating envelope will be found in the future observations.

New Crystal Form of an Organic Nonlinear Optical Material, 8-(4‘-Acetylphenyl)-1,4-dioxa-8-azaspiro[4.5]decane (APDA)

A new crystal form of an organic nonlinear optical material, 8-(4‘-acetylphenyl)-1,4-dioxa-8-azaspiro[4.5]decane (APDA) was found in the crystal growth by plate sublimation. This new crystal structure belongs to the noncentrosymmetric class, orthorhombic P212121, and the unit-cell dimensions are a = 8.428 (8) A, b = 28.349 (3) A, c = 5.634 (2) A, V = 1346.0 (6) A3, Z = 4, which are different from previously reported, orthorhombic Pna21. The molecule in the P212121 crystal has less twisting and more bending in the structure than in Pna21. The APDA molecules are coupled in an antiparallel system in the P212121 crystal as if to compensate for the repulsion arising from dipole−dipole interactions. This is in contrast to the molecular alignment of the Pna21 crystal in which the molecules are arranged in the same direction. The molecular hyperpolarizabilities (β) and d coefficients of the new crystal form were investigated theoretically by semiempirical CNDO/S-CI.