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Effects of the interplay between electron–electron interaction and intrinsic spin–orbit interaction on the indirect RKKY coupling in graphene nanoflakes
摘要： The effects of electron–electron (e–e) interaction and intrinsic spin–orbit interaction (ISOI) on the maximum of the magnetization and the indirect RKKY (Ruderman–Kittel–Kasuya–Yosida) coupling between the magnetic impurities embedded in zig-zag graphene nanoflakes are investigated using the tight-binding Hamiltonian and the mean-field Hubbard model. The RKKY coupling energy values as a function of the e–e interaction strengths are plotted for different values of ISOI strength. The appearance of the e–e interaction and ISOI changes drastically the magnitude of the indirect coupling so that increasing or decreasing of the indirect coupling depends on strength of the e–e interaction and ISOI and the size of the nanoflake. The dependence of the RKKY coupling and the maximum of the magnetization on the positions of the magnetic impurities and the size of the system are studied. We find that the e–e interaction and the ISOI are responsible for changes of the magnetization along the zig-zag edges of the nanoflake.
关键词： spin-orbit interaction,electron-electron interaction,magnetization,graphene nanoflakes,RKKY coupling
更新于2025-09-19 17:15:36
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Spin excitations in laser-molecular-beam epitaxy grown nanosized YIG films: towards low relaxation and desirable magnetization profile
摘要： We describe synthesis of nanosized Y3Fe5O12 (YIG) films grown by laser-molecular-beam epitaxy on Gd3Ga5O12 (GGG) and Nd3Ga5O12 (NdGG) substrates with (111) orientation and present results of ferromagnetic resonance (FMR) and spin wave propagation studies in these heterostructures. It is found that magnetic parameters of YIG films grown on NdGG and GGG substrates are considerably different. FMR spectra of YIG/NdGG structures are characterized by a large number of narrow peaks, while FMR spectra of YIG/GGG structures consist of a small number of peaks or one peak. The effective magnetization of YIG films grown on NdGG substrates is less than that of YIG films grown on GGG and is more sensitive to the growth conditions. A lateral inhomogeneity of YIG/NdGG structures is observed in spin wave propagation experiments. For YIG/NdGG and YIG/GGG structures the FMR linewidth ?H of a single peak sharply increases with temperature decrease from 298 to 67 K. The observed increase of ?H is explained by typical relaxation processes caused by the presence of Fe2+ ions. From the spin-wave propagation study it is also found that relaxation of spin-waves explains only a minor part of the FMR single peak linewidth in YIG/NdGG structures. On the basis of obtained results, YIG/GGG/semiconductor- and YIG/NdGG/semiconductor-heterostructures with expected low spin-wave relaxation and desirable effective magnetization profile are proposed.
关键词： magnetization profile,ferromagnetic resonance,spin wave propagation,laser-molecular-beam epitaxy,YIG films
更新于2025-09-19 17:13:59
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Electric bias-controlled switching of magnetization of ferrimagnetically coupled Mn delta-layers in a GaAs-AlGaAs quantum well
摘要： We suggest a model of synthetic ferrimagnetic semiconductor structure based on GaAs-AlGaAs quantum well doped by two Mn delta-layers. The coupling between the delta-layers is mediated by extra holes, and can be switched between ferro- and antiferromagnetic one by gating the structure. A proper choice of Mn concentrations in the delta-layers and of local degree of disorder enables fabrication of a ferrimagnetic structure supporting ultrafast switching of magnetization by short pulses of electric bias without an external magnetic field. The switching mechanism in the structure relies on kinetic spin exchange between the two delta-layers which is mediated by exchange scattering of electric-pulse heated holes by magnetic ions within the layers. Owing to specific interplay between characteristics of the exchange scattering, spin decay times, and the heat withdraw in the suggested synthetic ferrimagnetic semiconductor, the necessary parameters of electric-bias pulse are within the technologically accessible range, and do not contradict typical thermal kinetics of semiconductor structures.
关键词： ultrafast heating,GaAs quantum well,synthetic ferrimagnet,ultrafast switching of magnetization
更新于2025-09-19 17:13:59
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Rationally assembled nonanuclear lanthanide clusters: Dy <sub/>9</sub> displays slow relaxation of magnetization and Tb <sub/>9</sub> serves as luminescent sensor for Fe <sup>3+</sup> , CrO <sub/>4</sub><sup>2?</sup> and Cr <sub/>2</sub> O <sub/>7</sub><sup>2?</sup>
摘要： The utilization of a Schi? base ligand 2-((2-hydroxy-4-methoxy-benzylideneamino)methyl)phenol (H2L) a?orded five nonanuclear lanthanide(III) clusters of formula [Ln9L8(m3-OH)8(m5-O)2(DMF)8][H3O](cid:3)nH2O (Ln = Eu, n = 1 (1[H3O](cid:3)H2O); Ln = Gd, n = 4 (2[H3O](cid:3)4H2O); Ln = Tb, n = 3 (3[H3O](cid:3)3H2O); Ln = Dy, n = 6 (4[H3O](cid:3)6H2O); Ln = Ho, n = 2 (5[H3O](cid:3)2H2O)). Single-crystal X-ray di?raction analysis revealed that all of the complexes were isomorphous and had a diabolo-like topology. The intriguing Ln9 core was constructed by two square pyramidal units that shared a vertex metal centre. Variable-temperature dc magnetic susceptibility studies indicated weak antiferromagnetic interactions for 2[H3O](cid:3)4H2O, 3[H3O](cid:3)3H2O, 4[H3O](cid:3)6H2O and 5[H3O](cid:3)2H2O. The DyIII 9 cluster displayed a slow relaxation of magnetization. Fluorescence measurements revealed an intense green photoluminescence for the TbIII 9 compound. The luminescence tests showed that the TbIII 9 analogue could perform as a highly sensitive, selective and recyclable luminescence sensing material for Fe3+, CrO4 2(cid:2). In this work, the H2L ligand was derived by finely modifying the previously designed compounds (((2-hydroxy-3-methoxybenzyl)imino)- 2(cid:2) and Cr2O7 2(cid:2)? *a and methyl)-6-ethoxyphenol and (((2-hydroxy-3-methoxybenzyl)imino)methyl)-6-methoxyphenol, from which the Ln2 and Ln4 clusters were successfully prepared and reported. Noticeably, the decisive decrease in the steric hindrance of the predesigned ligands resulted in the expansion of the nuclearity. This work demonstrated the synthetic potential for assembling the large clusters by rationally decreasing the steric rsc.li/njc hindrance of the analogous ligands.
关键词： magnetization,Fe3+,CrO4 2(cid:2),luminescent sensor,Cr2O7 2(cid:2),lanthanide clusters
更新于2025-09-16 10:30:52
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Precession damping in [Co <sub/>60</sub> Fe <sub/>40</sub> /Pt] <sub/>5</sub> multilayers with varying magnetic homogeneity investigated with femtosecond laser pulses
摘要： We report on the ultrafast magnetization dynamics of [Co60Fe40/Pt]5 multilayers studied with femtosecond laser pulses. The samples were grown at room temperature by DC magnetron sputtering with Ta capping and Pt buffer layers and present the same thickness and perpendicular magnetic anisotropy as determined by vibrating sample magnetometry. Controlled growth rate of the Pt buffer layer modified the anisotropy fields and magnetic domain sizes as measured by magnetic force microscopy (MFM). An estimation of the average magnetic domain sizes was obtained from the profile of the self-correlation transform of the MFM images. For multilayers having an average magnetic domain size of 490 nm, we report a damped precession of the magnetization which decays with a time constant of ～100 ps and which has a frequency which varies from 8.4 GHz to 17.0 GHz as the external field increases from 192 mT to 398 mT. Fitting the precession dynamics with the Landau-Lifshitz-Gilbert equation we evaluated the damping α, which decreases from 0.18 to 0.05 with increasing magnetic domain sizes (127 nm to 490 nm). These α values are higher than for single layers suggesting an enhanced scattering and spin pumping effects from the Pt adjacent layers. In addition, the precession frequency increases from 2.04 GHz to 11.50 GHz as the anisotropy field of the multilayers increases from 6.5 kOe to 13.0 kOe. Finally, a comparative analysis between micromagnetic simulations and MFM images allowed us to determine the exchange stiffness (Aex) in the [Co60Fe40/Pt]5 multilayers.
关键词： exchange stiffness,femtosecond laser pulses,Landau-Lifshitz-Gilbert equation,[Co60Fe40/Pt]5 multilayers,damping,magnetic force microscopy,ultrafast magnetization dynamics,perpendicular magnetic anisotropy
更新于2025-09-12 10:27:22
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Magnetization reversal in NiFe <sub/>2</sub> O4/SrTiO <sub/>3</sub> nanoheterostructures grown by laser molecular beam epitaxy
摘要： NiFe2O4/SrTiO3(001) nanoheterostructures have been fabricated by laser molecular beam epitaxy method. Surface morphology and crystal structure of Ni-ferrite films were analysed by atomic force microscopy (AFM), reflection of high energy electron diffraction (RHEED), X-ray diffraction (XRD). X-ray methods prove the presence of inverse spinel crystal structure of films that was confirmed by measurements of spectral dependence of optical polar Kerr (PMOKE) effect. Study of magnetization reversal for different orientations of magnetic field carried out by vibration sample magnetometry (VSM) and longitudinal magneto-optical Kerr effect (LMOKE) are presented. In-plane magnetization loops exhibit 90 period indicating presence of biaxial magnetic anisotropy. Asymmetry of LMOKE hysteresis loops is related to manifestation of quadratic in magnetization effects in reflection of light.
关键词： nanoheterostructures,NiFe2O4/SrTiO3,biaxial magnetic anisotropy,laser molecular beam epitaxy,magnetization reversal
更新于2025-09-12 10:27:22
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Plasmonic layer-selective all-optical switching of magnetization with nanometer resolution
摘要： All-optical magnetization reversal with femtosecond laser pulses facilitates the fastest and least dissipative magnetic recording, but writing magnetic bits with spatial resolution better than the wavelength of light has so far been seen as a major challenge. Here, we demonstrate that a single femtosecond laser pulse of wavelength 800 nm can be used to toggle the magnetization exclusively within one of two 10-nm thick magnetic nanolayers, separated by just 80 nm, without affecting the other one. The choice of the addressed layer is enabled by the excitation of a plasmon-polariton at a targeted interface of the nanostructure, and realized merely by rotating the polarization-axis of the linearly-polarized ultrashort optical pulse by 90°. Our results unveil a robust tool that can be deployed to reliably switch magnetization in targeted nanolayers of heterostructures, and paves the way to increasing the storage density of opto-magnetic recording by a factor of at least 2.
关键词： femtosecond laser pulses,plasmon-polariton,storage density,magnetic recording,all-optical magnetization reversal
更新于2025-09-11 14:15:04
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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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The enhanced magnetoelectric effect and piezoelectric properties in the lead-free Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 nano-multilayers composite thin films
摘要： The lead-free multiferroic nano-multilayers composite thin films were fabricated on basis of ferroelectric (FE) Bi3.15Nd0.85Ti3O12 (BNT) and ferromagnetic (FM) La0.7Ca0.3MnO3 (LCMO) parents with 8 nm/6 nm periodicity, respectively. The crystal structure, switching of polarization, magnetization and temperature dependence of magnetoelectric coupling (ME) effect for the multiferroic BNT/LCMO composite thin films were investigated in detail, respectively. Ferroelectric behavior along with an enhanced remnant polarization (2Pr) of 42 mC/cm2, saturated magnetization around 151 emu/cm3, the enhanced piezoelectric coefficient d33 of 263 pm/V and the enhanced magnetoelectric effect voltage coefficient of 72.1 mV/cm*Oe were obtained. The results show that the lead-free multiferroic films exhibit both good ferroelectric, dielectric and magnetic properties, as well as the enhanced ME effects, indicating that the coupling effects of electric and magnetic field exist in the fabricated Bi3.15Nd0.85Ti3O12/La0.7Ca0.3MnO3 (BNT/LCMO) nano-multilayer thin films, and the strong ME effect originating from the magnetic-mechanical-electric interaction and interface coupling were demonstrated. These results can be particularly important for developing nano-composite multiferroic devices.
关键词： Temperature dependence of ME effect,Lead-free BNT/LCMO nano-multilayers,Ferroelectric properties,Magnetization
更新于2025-09-10 09:29:36
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hybride nanowire networks prepared by electrospinning
摘要： We prepared La1.85Sr0.15CuO4/La0.7Sr0.3MnO3 nanowire network hybrid systems by means of electrospinning. From obervation by scanning electron microscopy, the average diameter of the nanowires is around 220 nm and the average length can reach over 50 μm. The randomly aligned La1.85Sr0.15CuO4 and La0.7Sr0.3MnO3 nanowires exhibit numerous interconnects among each other and form a complicated, non woven hybrid network system. The nanowires are polycrystalline with a grain size at around 30 nm as con?rmed by transmission electron microscopy. According to four-probe electrical transportation and magnetization measurements, superconductivity of the sample is suppressed and a positive magnetoresistance e?ect is observed. Measurements of M(T ) and M(H) were carried out as well, revealing the soft magnetic character of the hybrid nanowire network samples.
关键词： LSCO,electrospinning,nanowires,LSMO,magnetization,magnetoresistance,hybrid network
更新于2025-09-10 09:29:36