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Néel transition in the multiferroic BiFeO <sub/>3</sub> -0.25PbTiO <sub/>3</sub> nanoparticles with anomalous size effect
摘要： The role of size reduction on the structural parameters, antiferromagnetic transition temperature (TN), and spin reorientation transition temperature of BiFeO3-0.25PbTiO3 (BF-0.25PT) has been studied. Rietveld analysis using high resolution synchrotron x-ray powder diffraction data confirms that the space group of BF-0.25PT solid solutions is monoclinic Cc and not rhombohedral R3c for both bulk and nanocrystalline powders. This settles a longstanding controversy about the structure of these solid solutions toward the BiFeO3 rich end of the morphotropic phase boundary in the BiFeO3-xPbTiO3 system. Using magnetization and neutron powder diffraction data, we show that the Néel transition temperature (TN) of BF-0.25PT increases from 445 K for bulk to 480 K for 150 nm particle size. This is in marked contrast to the scaling theories of phase transitions in finite size systems. We also show that the spin reorientation transition occurring below TN in bulk monoclinic compositions like BF-0.25PT is suppressed in the nanocrystalline samples of ～150 nm particle size. Based on Rietveld refined structural parameters, we show that the asymmetry and non-linearity of the Fe-O-Fe superexchange pathways grow with decreasing particle size and that they exhibit a strong correlation with TN. We believe that the substantially enhanced Dzyaloshinskii-Moriya interaction with decreasing particle size as a result of asymmetric and non-collinear Fe-O-Fe superexchange pathways may be the key factor in raising the TN on decreasing the particle size. These observations present a new facet of type-I multiferroic materials, where superexchange pathways are intimately dependent on the ferroelectric distortion.
关键词： multiferroic,antiferromagnetic transition,BiFeO3-PbTiO3,size effect,Dzyaloshinskii-Moriya interaction,Néel transition,nanoparticles
更新于2025-09-23 15:23:52
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Influence of the capping layer material on the interfacial Dzyaloshinskii-Moriya interaction in Pt/Co/capping layer structures probed by Brillouin light scattering<sup></sup>
摘要： Influence of the capping layer material on the interfacial Dzyaloshinskii-Moriya interaction in Pt/Co/capping layer structures probed by Brillouin light scattering. Co ultrathin films, of various thicknesses (0.8 nm ≤ tCo ≤ 2.5 nm), have been grown by sputtering on Si substrates, using Pt buffer layers and different capping layers (Cu, Ir, MgO and Pt). The x-ray diffraction revealed that our films have a (111) out-of-plane texture with various degrees of strains. Their magnetic properties have been studied by vibrating sample magnetometry (VSM) and Brillouin light scattering (BLS) in the Damon-Eshbach geometry. VSM characterizations revealed that films with Co thickness below (above) the spin reorientation transition thickness, which is capping layer dependent, are perpendicularly (in-plane) magnetized, suggesting the existence of an interface anisotropy. The magnetic dead layer has been taken into account to precisely determine the surface anisotropy constant was found to be 1.42 ± 0.02 erg/cm2 and of 1.33 ± 0.02 erg/cm2 for the Pt/Co/Cu and Pt/Co/Ir samples, respectively, suggesting that it is due to the Pt/Co interface and that the top Co/Cu or Co/Ir interfaces have a negligible contribution. A lower value of 1.07 ± 0.02 erg/cm2 has been obtained for Pt/Co/MgO most probably due to over-oxidation of Co at the Co/MgO interface. The BLS measurements revealed a pronounced nonreciprocal spin waves propagation, due to the interfacial Dzyaloshinskii-Moriya interaction (iDMI) induced by Pt interface with Co, which increases with decreasing Co thickness. The surface iDMI constant Ds estimated at -0.8 pJ/m, -1.05 pJ/m and –0.95 pJ/m, respectively for Pt/Co/Ir, Pt/Co/Cu and Pt/Co/MgO for the samples where a linear thickness dependence of the effective iDMI constant has been observed.
关键词： Dzyaloshinskii-Moriya interaction,Brillouin light scattering,spin waves and Perpendicular magnetic anisotropy,Interface effects
更新于2025-09-23 15:22:29
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seed layers
摘要： We characterize asymmetric growth of magnetic bubble domains in perpendicularly magnetized Co/Ni multilayers grown on PtxIr1?x seed layers by application of perpendicular and in-plane magnetic fields. Using a refined model of domain wall creep that incorporates contributions from the anisotropic elastic energy, ε, and a chirality-dependent prefactor, v0, we elucidate factors that govern the mobility of Dzyaloshinskii domain walls as a function of seed-layer composition. The interfacial Dzyaloshinskii-Moriya interaction (DMI) magnitude is found to decrease monotonically with xIr, which is independently confirmed by Brillouin light scattering. Moreover, the persistence of significant asymmetry in velocity curves across the full composition range supports previous assertions that a chirality-dependent attempt frequency akin to chiral damping could play a critical role in the observed trends. This work helps resolve fundamental questions about the factors governing Dzyaloshinskii domain-wall creep and demonstrates varying Pt-Ir seed-layer composition as a method to tune DMI.
关键词： Dzyaloshinskii domain-wall creep,PtxIr1?x seed layers,Brillouin light scattering,interfacial Dzyaloshinskii-Moriya interaction,Co/Ni thin films
更新于2025-09-23 15:21:21
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-electron materials: Sn monolayer on a SiC(0001) surface
摘要： Materials with sp magnetism demonstrate strongly nonlocal Coulomb interactions, which opens a way to probe correlations in the regimes not achievable in transition metal compounds. By the example of Sn monolayer on a SiC(0001) surface, we show that such systems exhibit unusual but intriguing magnetic properties at the nanoscale. Physically, this is attributed to the presence of a significant ferromagnetic coupling, the so-called direct exchange, which fully compensates ubiquitous antiferromagnetic interactions of the superexchange origin. Having a nonlocal nature, the direct exchange was previously ignored because it cannot be captured within the conventional density functional methods and significantly challenges ground state models earlier proposed for Sn/SiC(0001). Furthermore, heavy adatoms induce strong spin-orbit coupling, which leads to a highly anisotropic form of the spin Hamiltonian, in which the Dzyaloshinskii-Moriya interaction (DMI) is dominant. The latter is suggested to be responsible for the formation of a nanoskyrmion state at realistic magnetic fields and temperatures.
关键词： Dzyaloshinskii-Moriya interaction,SiC(0001) surface,direct exchange,nonlocal Coulomb interactions,nanoskyrmion state,sp magnetism,Sn monolayer
更新于2025-09-23 15:21:21
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Generation of magnetic skyrmions by focused vortex laser pulses
摘要： We propose a method to generate magnetic skyrmions by intense laser pulses optimally focused on a magnetically ordered 2D-layer. In particular, we consider few-cycle intense pulses with the magnetic vortex structure near the focus region on the layer. The spin dynamics is modeled using the Landau–Lifshitz–Gilbert equation and includes the Dzyaloshinskii–Moriya interaction. We demonstrate that skyrmions can be observed within a few picoseconds after the end of the laser pulse. We analyze the physical picture of this process and work out which laser pulse and 2D-layer parameters are required for the generation.
关键词： Dzyaloshinskii–Moriya interaction,laser pulses,Landau–Lifshitz–Gilbert equation,magnetic skyrmions
更新于2025-09-23 15:21:01
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Whirling spins with a ferroelectric
摘要： Ferroelectric polarization enables the emergence and control of magnetic skyrmions at an oxide interface. Controlling magnetism with an electric field is a burgeoning scientific challenge with significant technological implications. The reduced power required to electrically manipulate magnetization opens up exciting prospects for functional devices with unprecedented performance. Ferroelectric materials are especially suitable because they possess spontaneous electric polarization, switchable by an applied electric field. A ferroelectric interfaced with a thin-film ferromagnet has already been shown to modify the electronic structure of the ferromagnet near the interface, allowing control of properties such as the interfacial magnetization and magnetic order via ferroelectric polarization. Now, writing in Nature Materials, Lingfei Wang and colleagues put a new spin on ferroelectric-controlled nanoscale magnetism. They demonstrate a strategy for creating and manipulating magnetic nanoscale vortices, so-called skyrmions, using intrinsic ferroelectric polarization at oxide interfaces.
关键词： oxide interface,ferroelectric polarization,skyrmions,nanoscale magnetism,Dzyaloshinskii–Moriya interaction
更新于2025-09-23 15:21:01
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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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Magnetic phase transitions of insulating spin-orbit coupled Bose atoms in one-dimensional optical lattices
摘要： We consider the insulating spin-orbit coupled Bose atoms con?ned within one-dimensional optical lattices and explore their ground-state magnetic phase transitions. Under strong interactions, the charge degrees of atoms are frozen and the system can be described by an anisotropic XXZ Heisenberg chain with Dzyaloshinskii-Moriya interaction and transverse ?eld. We apply the matrix product state method to obtain the ground states, and analyze spiral correlation functions, spin-spin correlation functions, and ?rst energy gap. Under weakly transverse ?elds, the ground state is a ferromagnetic phase if the interspin s-wave interaction strength is stronger than that of the intraspin ones, otherwise, it is a paramagnetic phase, an antiferromagnetic phase, or a gapless spiral phase with algebraic decaying spin correlations. When the transverse ?eld is strengthened, the gapless spiral phase is broken and a new spiral phase with long-range spin-spin correlations emerges.
关键词： optical lattices,XXZ Heisenberg chain,Bose atoms,magnetic phase transitions,Dzyaloshinskii-Moriya interaction,spin-orbit coupling,matrix product state method,transverse ?eld
更新于2025-09-12 10:27:22
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trilayers
摘要： Chiral domain walls in ultrathin perpendicularly magnetized layers have a Néel structure stabilized by a Dzyaloshinskii-Moriya interaction (DMI) that is generated at the interface between the ferromagnet and a heavy metal. Different interface materials or properties are required above and below a ferromagnetic film in order to generate the structural inversion asymmetry needed to ensure that the DMI arising at the two interfaces does not cancel. Here we report on the magnetic properties of epitaxial Pt/Co/AuxPt1?x trilayers grown by sputtering onto sapphire substrates with 0.6 nm thick Co. As x rises from 0 to 1, a structural inversion asymmetry is progressively generated. We characterize the epilayer structure with x-ray diffraction and cross-sectional transmission electron microscopy, revealing (111) stacking. The saturation magnetization falls as the proximity magnetization in Pt is reduced, whilst the perpendicular magnetic anisotropy Ku rises. The micromagnetic DMI strength D was determined using the bubble expansion technique and also rises from a negligible value when x = 0 to ～1 mJ/m2 for x = 1. The depinning field at which field-driven domain wall motion crosses from the creep to the depinning regime rises from ～40 to ～70 mT, attributed to greater spatial fluctuations of the domain wall energy with increasing Au concentration. Meanwhile, the increase in DMI causes the Walker field to rise from ～10 to ～280 mT, meaning that only in the x = 1 sample is the steady flow regime accessible. The full dependence of domain wall velocity on driving field bears little resemblance to the prediction of a simple one-dimensional model, but can be described very well using micromagnetic simulations with a realistic model of disorder. These reveal a rise in Gilbert damping as x increases.
关键词： perpendicular magnetic anisotropy,Gilbert damping,Chiral domain walls,domain wall dynamics,Dzyaloshinskii-Moriya interaction
更新于2025-09-04 15:30:14