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Domain wall dynamics due to femtosecond laser-induced superdiffusive spin transport
摘要： Manipulation of magnetic domain walls via a helicity-independent laser pulse has recently been experimentally demonstrated and various physical mechanisms leading to domain wall dynamics have been discussed. Spin-dependent superdiffusive transport of hot electrons has been identified as one of the possible ways to affect a magnetic domain wall. Here, we develop a model based on superdiffusive spin-dependent transport to study the laser-induced transport of hot electrons through a smooth magnetic domain wall. We show that the spin transfer between neighboring domains can enhance ultrafast demagnetization in the domain wall. More importantly, our calculations reveal that when the laser pulse is properly focused onto the vicinity of the domain wall, it can excite sufficiently strong spin currents to generate a spin-transfer torque that can rapidly move the magnetic domain wall by several nanometers in several hundred femtoseconds, leading to a huge nonequilibrium domain wall velocity.
关键词： spin-transfer torque,ultrafast demagnetization,magnetic domain walls,superdiffusive spin transport,laser-induced dynamics
更新于2025-09-23 15:21:01
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Extreme asymmetry of Néel domain walls in multilayered films of the dilute magnetic semiconductor (Ga,Mn)(As,P)
摘要： We report on unconventional perfectly shaped, fully asymmetric ～90? Néel domain walls in multilayered ?lms of the diluted ferromagnetic semiconductor (Ga,Mn)(As,P) with a stepwise variation of P doping. Our results contradict micromagnetic calculations, which favor symmetric domain walls due to crystallographic anisotropy and stray ?eld energy. We demonstrate that both the puzzling uniaxial in-plane anisotropy in the tetragonal multilayered ?lm and the asymmetry of the domain walls could result from Dzyaloshinskii-Moriya interactions that are enhanced by the multiple sharp interfaces between the layers and from anisotropic nonrelativistic exchange coupling. Our ?nding shows that digital variations of composition during the molecular beam epitaxy can be used to tune the anisotropy and chirality of magnetic multilayers.
关键词： diluted magnetic semiconductor,Dzyaloshinskii-Moriya interactions,magnetic anisotropy,Néel domain walls,molecular beam epitaxy
更新于2025-09-23 15:21:01
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Tailoring properties of hybrid perovskites by domain-width engineering with charged walls
摘要： Charged ferroelectric domain walls are fascinating electrical topological defects that can exhibit unusual properties. Here, in the search for novel phenomena, we perform and analyze first-principles calculations to investigate the effect of domain width on properties of domains with charged walls in the photovoltaic material consisting of methylammonium lead iodide hybrid perovskite. We report that such domains are stable and have rather low domain wall energy for any investigated width (that is, up to 13 lattice constants). Increasing the domain width first linearly decreases the electronic band gap from ?1.4 eV to about zero (which therefore provides an efficient band-gap engineering), before the system undergoes an insulator-to-metal transition and then remains metallic (with both the tail-to-tail and head-to-head domain walls being conductive) for the largest widths. All these results can be understood in terms of: (i) components of polarization along the normal of the domain walls being small in magnitude; (ii) an internal electric field that is basically independent of the domain width; and (iii) rather negligible charge transfer between walls. These findings deepen the knowledge of charged ferroelectric domain walls and can further broaden their potential for applications, particularly in the context of halide perovskites for photovoltaics.
关键词： charged ferroelectric domain walls,hybrid perovskites,photovoltaic materials,band-gap engineering,insulator-to-metal transition
更新于2025-09-23 15:19:57
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Speckled cross-spectral densities and their associated correlation singularities for a modern source of partially coherent x rays
摘要： We consider a realistic model for calculating the cross-spectral density of partially coherent beams from an x-ray undulator in a modern storage ring. This two-point coherence function is seen to have a speckled structure associated with the presence of x-ray coherence vortices and domain walls. Such cross-spectral density speckle is associated with a network of spatial pairs of points for which there is zero correlation. X-ray coherence vortices and domain walls are seen to emerge naturally as the number of coherent modes required increases. An understanding of the existence and nature of such correlation singularities enhances our ability to exploit partially coherent x-ray radiation from new or upgraded synchrotron sources, for both imaging and diffraction applications.
关键词： cross-spectral density,synchrotron sources,coherence vortices,domain walls,partially coherent beams,x-ray undulator
更新于2025-09-12 10:27:22
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Enhanced Interfacial Dzyaloshinskii?Moriya Interaction in annealed Pt/Co/MgO structures
摘要： The interfacial Dzyaloshinskii?Moriya interaction (iDMI) is attracting great interests for spintronics. An enhancement of iDMI with an atomically thin insertion of Ta and Mg is comprehensively understood with the help of ab-initio calculations. Thermal annealing has been used to crystallize the MgO thin layer for improving tunneling magneto-resistance (TMR), but interestingly it also provides a further increase of the iDMI constant. An increase of the iDMI constant up to 3.3 mJ m2? is shown, which could be promising for the scaling down of skyrmion electronics.
关键词： domain-walls (DW),Dzyaloshinskii?Moriya interaction (DMI),inserted layer,annealing
更新于2025-09-12 10:27:22
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Effects of end-on oriented polymer chains at the donor/acceptor interface in organic solar cells
摘要： The transport and magnetic properties of LaAlO3/SrTiO3 (LAO/STO) heterostructure have been studied during cooling and warming. The strain gradient perpendicular to the surface of the heterostructure increases with the thickness of LAO film. The conductivity accelerated recoveries (CAR) are found at 80 K and 176 K in the interface of LAO/STO sample with millimeter scale, and are more obvious for thicker LAO layers during warming. These two recovering temperatures correspond to the migrating energies of oxygen single vacancy and divacancy trapped by polarized domain walls, separately. This indicated that domain walls diffuse along the longitudinal direction and expand to larger area due the strain gradient perpendicular to the interface. The stable and precise accelerating recovering temperatures make the sample at a larger scale a potential widely applied temperature standard reference. The magnetization measurements reveal the coexistence of paramagnetic and diamagnetic in the LAO/STO samples at whole temperature from 2 K to 300 K. The abnormal electric resistance rise is observed with the decreasing temperature below 25 K for the samples of 7 and 15 LAO layers. This anomaly is attributed to the Kondo effect below 25 K and weak anti-localization below 5 K due to the weightier paramagnetic content. The larger diamagnetic content suppresses these contributions in 25 LAO layers sample. This work provided an insightful view that the strain modified structure domain leads to the enhancement of CAR effect, which helps to achieve a better understanding of domain related physics in the LAO/STO system.
关键词： magnetization,LaAlO3/SrTiO3 heterostructure,conductivity accelerated recoveries,domain walls,weak anti-localization,strain gradient,Kondo effect
更新于2025-09-11 14:15:04
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Oxygen vacancies in the bulk and at neutral domain walls in hexagonal
摘要： We use density functional calculations to investigate the accommodation and migration of oxygen vacancies in bulk hexagonal YMnO3, and to study interactions between neutral ferroelectric domain walls and oxygen vacancies. Our calculations show that oxygen vacancies in bulk YMnO3 are more stable in the Mn-O layers than in the Y-O layers. Migration barriers of the planar oxygen vacancies are high compared to oxygen vacancies in perovskites, and to previously reported values for oxygen interstitials in h-YMnO3. The calculated polarization decreases linearly with vacancy concentration, while the out-of-plane lattice parameter expands in agreement with previous experiments. In contrast to ferroelectric perovskites, oxygen vacancies are found to be more stable in bulk than at domain walls. The tendency of oxygen vacancies to segregate away from neutral domain walls is explained by unfavorable Y-O bond lengths caused by the local strain field at the domain walls.
关键词： oxygen vacancies,ferroelectric domain walls,hexagonal YMnO3,density functional calculations,migration barriers
更新于2025-09-11 14:15:04
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Understanding and predicting geometrical constraint ferroelectric charged domain walls in a BiFeO <sub/>3</sub> island via phase-field simulations
摘要： It has been known that ferroelectric charged domain walls (CDWs), which break the polarization continuity, may be electrically active with an elevated conductivity. However, the bound charge at CDWs may render them energetically unstable, and thus, forming CDWs naturally and manipulating them electrically is still challenging. Here, we theoretically utilize phase-field simulations to design spontaneously generated CDWs with center-type quad-domains in a single square-shaped BiFeO3 nanoisland. It is shown that the stability of the spontaneously emerging head-to-head domain walls with center-convergent quad-domains is mainly determined by three contributions, namely, the geometrical constraint from approximately 45°-tilted bottom edges, the electric boundary condition, and the necessary screening free charges to compensate head-to-head domain walls. It is demonstrated that the center-convergent quad-domains with head-to-head CDWs can be electrically switched to the center-divergent one with tail-to-tail CDWs, providing guidance for achieving ferroelectric domain-wall-based nanodevices with low-power dissipation.
关键词： phase-field simulations,electric boundary condition,ferroelectric charged domain walls,BiFeO3,screening free charges,geometrical constraint
更新于2025-09-10 09:29:36
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Frequency-dependent decoupling of domain-wall motion and lattice strain in bismuth ferrite
摘要： Dynamics of domain walls are among the main features that control strain mechanisms in ferroic materials. Here, we demonstrate that the domain-wall-controlled piezoelectric behaviour in multiferroic BiFeO3 is distinct from that reported in classical ferroelectrics. In situ X-ray diffraction was used to separate the electric-field-induced lattice strain and strain due to displacements of non-180° domain walls in polycrystalline BiFeO3 over a wide frequency range. These piezoelectric strain mechanisms have opposing trends as a function of frequency. The lattice strain increases with increasing frequency, showing negative piezoelectric phase angle (i.e., strain leads the electric field), an unusual feature so far demonstrated only in the total macroscopic piezoelectric response. Domain-wall motion exhibits the opposite behaviour, it decreases in magnitude with increasing frequency, showing more common positive piezoelectric phase angle (i.e., strain lags behind the electric field). Charge redistribution at conducting domain walls, oriented differently in different grain families, is demonstrated to be the cause.
关键词： frequency dispersion,BiFeO3,domain walls,piezoelectric,lattice strain
更新于2025-09-10 09:29:36
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Imaging Domains in a Zero-Moment Half Metal
摘要： We have a choice of methods for examining domains at the surface of a ferromagnet that depend on probing the stray ?eld distribution, but these methods do not work in antiferromagnets or compensated ferrimagnets, which produce no stray ?eld. The discovery of compensated ferrimagnetic half metals allows for the local magnetization state to be observed directly with polarized light. The example considered here, Mn2RuxGa, has two inequivalent but oppositely aligned Mn sublattices with equal and opposite moments, but only one of them contributes spin-polarized conduction electrons at the Fermi energy. The material looks like an antiferromagnet from the outside, but from the point of view of the electronic structure, it resembles a spin-polarized ferromagnetic metal. The anisotropy axis is perpendicular to the ?lm plane, which allows domains to be imaged directly by polar magneto-optic Kerr effect. The domain structure in a ?lm with a composition of Mn2Ru0.4Ga has been imaged in a Kerr microscope and hysteresis loops have been traced. Domains have dimensions of order 20 μm with meandering domain walls and a fractal dimension D f = 1.85. Our results open new direct imaging possibilities of magnetically ordered materials with no net moment.
关键词： compensated ferrimagnets,Mn2RuxGa (MRG),half metal,Kerr microscopy,Antiferromagnetic domain walls
更新于2025-09-10 09:29:36