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We report on x-ray and neutron scattering studies that reveal the structure of interfaces of C60 layers with adjacent transition metal layers, in this instance, Cu. Such interfaces produce room-temperature long-range spin order that is not described by conventional theories of metallic magnetism. We use a combination of hard x-ray reflectivity and neutron scattering to investigate the interfacial structure of two C60/Cu layered samples: a superlattice with multiple C60/Cu repeats and a simpler tri-layer structure. For both structures, we develop a consistent structural model for the two scattering techniques, which details the critical interfacial roughness between the layers. We find that while x-ray reflectivity provides a strong contrast between the C60 and Cu layers, the similar neutron scattering length density of the two materials severely reduces the neutron scattering contrast. Our results can be used to design material systems that permit studies of the magnetism of the C60/transition metal interfaces with spin-sensitive scattering probes such as polarized neutron reflectometry. [ABSTRACT FROM AUTHOR]

We present measurements of element- and time-resolved ferromagnetic resonance (FMR) in magnetic thin films at gigahertz frequencies via an implementation of time-resolved x-ray magnetic circular dichroism (TR-XMCD). By combining TR-XMCD and FMR, using a rf excitation that is phase locked to the photon bunch clock, the dynamic response of individual layers or precession of individual elements in an alloy can be measured. The technique also provides extremely accurate measurements of the precession cone angle (to 0.1°) and the phase of oscillation (to 2°, or ∼5 ps at 2.3 GHz). TR-XMCD combined with FMR can be used to study the origins of precessional damping by measuring the relative phase of dissimilar precessing magnetic moments. We have used the technique to measure the response of specific elements and separate layers in several alloys and structures, including a single Ni81Fe19 layer, a pseudo-spin-valve structure (Ni81Fe19/Cu/Co93Zr7), magnetic bilayers consisting of low damping (Co93Zr7) and high damping (Tb-doped Ni81Fe19) layers joined across a common interface, and elemental moments in Tb-doped Ni81Fe19. [ABSTRACT FROM AUTHOR]

Epitaxial Fe48Rh52 thin films of nominal thickness 500 Å were grown on MgO (001) substrates via molecular beam epitaxy and capped with 20 Å of either Au or MgO. The presence of the anticipated magnetostructural phase transition from antiferromagnetism to ferromagnetism at ∼350 K was confirmed by superconducting quantum interference device and magneto-optic Kerr effect magnetometry. X-ray magnetic circular dichroism (XMCD) experiments were carried out at the L2,3 edges; measurements were done in both total electron yield (TEY) mode and indirect transmission mode. At room temperature, the indirect transmission XMCD data show no detectable dichroism, consistent with bulk antiferromagnetic behavior. However, room-temperature TEY data originating from the films’ surface reveal an appreciable dichroic signal indicating the presence of ferromagnetism. This near-surface/interfacial magnetism may be modified by choice of capping layer; the MgO-capped sample exhibited a considerably smaller ferromagnetic XMCD signal. The results have potential impact on the application of FeRh thin films as temperature-variable pinning layers in exchanged-biased systems. [ABSTRACT FROM AUTHOR]

We investigated thin La0.7Sr0.3MnO3-SrTiO3 heterostructures, where the band alignment is engineered by a variation of La/Sr stoichiometry only at the interface. In thin films, the engineered interface leads to an enhancement of the reversed spin configuration that mimics bulk behavior. Microscopically, this enhancement is closely connected with an increased magnetic anisotropy as well as intercoupling between an eg orbital reconstruction and a corresponding anisotropic lattice fluctuation. Furthermore, a reentrant-type behavior, triggered by this intercoupling, is observed in the remanent spin state. This microscopic perspective leads to insights on developing new strategies for maintaining bulk-like properties even in very thin La0.7Sr0.3MnO3 heterostructures. [ABSTRACT FROM AUTHOR]

We present a compact sample holder equipped with electromagnets and high frequency transmission lines; the sample holder is intended for combined x-ray magnetic circular dichroism (XMCD) and ferromagnetic resonance measurements (FMR). Time-resolved measurements of resonant x-ray detected FMR during forced precession are enabled by use of a rf excitation that is phase-locked to the storage ring bunch clock. Several applications of the combined XMCD+FMR technique are presented, demonstrating the flexibility of the experimental design. [ABSTRACT FROM AUTHOR]

We report on an all-optical investigation of coupled spin excitation modes in a series of magnetic trilayer structures. Using time-resolved magneto-optic Kerr effect (tr-MOKE) magnetometry, we observe multi-mode coherent spin excitations in Ni 81 Fe 19 /Ru/ Co 49 Fe 49 V 2 multilayers even though the tr-MOKE optical detection is sensitive only to the Co 49 Fe 49 V 2 magnetization dynamics. Frequency shifts of the different modes indicate that the coupling between the Ni 81 Fe 19 and Co 49 Fe 49 V 2 layers varies from anti-ferromagnetic to ferromagnetic to uncoupled as the Ru spacer layer thickness is increased from 8 Å to 200 Å. The lifetime of the high frequency coherent oscillations in the Co 49 Fe 49 V 2 layer increases by over 200%–300% even in the case of uncoupled Ni 81 Fe 19 and Co 49 Fe 49 V 2 layers with a 200 Å thick Ru spacer. The results suggest an additional method to decrease the damping of high-moment alloys in layered magnetic nanostructures. [ABSTRACT FROM AUTHOR]

We present all-optical studies of spin dynamics in two classes of ferrimagnets. Both sets of experiments use table-top laser-based pump–probe techniques to examine the ultrafast and longer timescale spin excitations. We use the visible/near infra-red time-resolved magneto-optical Kerr effect (tr-MOKE) to follow the spin dynamics of a series of metallic (FeCo) 1 − x Gd x thin films with varying Gd content. Magnetic compensation in the films occurs at a Gd concentration of ≈ 26 % , and the spin dynamics of the films exhibit a non-monotonic variation in effective magnetization. We also examine spin dynamics in an insulating NiFe 2 O 4 spinel using ultrafast techniques up at extreme ultraviolet energies, which permit element-specific investigations. The element and time-resolved delay scans reveal a non-trivial interaction between spin excitations on the different magnetic sub-lattices of the magnetic insulator. [ABSTRACT FROM AUTHOR]

We present transmission-mode XMCD characterization of Fe, Ni, and Tb moment alignment in Tb-doped Ni81Fe19 thin films. The use of transmission geometry measurements has allowed the extraction of absolute projected elemental moments in the alloy. A very low projected Tb moment at 6% doping level, which nonetheless reverses with low applied fields (40 Oe), indicates a sperimagnetic alignment with respect to the Fe and Ni elements in the cosputtered polycrystalline alloy. [ABSTRACT FROM AUTHOR]

Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. Here, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni0.65Zn0.35Al0.8Fe1.2O4) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe2+/3+ and Ni2+ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within ≈ 2°. Moreover, the effective spin relaxation is identical to within <10% for all magnetic cations in the ferrite. Thus, we validate the oft-assumed "ferromagnetic-like" dynamics in the resonantly driven ferrimagnetic oxide: the magnetic moments from different cations precess as a coherent, collective magnetization, despite the high contents of nonmagnetic Zn2+ and Al3+ diluting the exchange interactions. [ABSTRACT FROM AUTHOR]

Objective: To assess whether outpatient cervical ripening with a synthetic osmotic dilator shortens the length of hospital stay in term pregnancies undergoing labor induction.Methods: Pregnant participants scheduled for labor induction at term with unfavorable cervix (less than 3-cm dilated and less than 60% effaced) and not requiring inpatient maternal or fetal monitoring were consented, and synthetic osmotic dilator rods were inserted on the day of scheduled induction. After reassuring fetal heart tracing, patients randomized to the outpatient group were asked to return 12 hours after insertion or sooner if needed. Those randomized to the inpatient group remained in the hospital. After the first round of ripening, additional ripening, oxytocin, and labor management were left up to the clinical health care professionals. The primary outcome was the proportion of participants with hospital stays longer than 48 hours. We estimated that a sample size of 338 would provide 85% power to detect a 30% difference between groups.Results: From November 2018 to November 2021, 339 participants were randomized (171 inpatient, 167 outpatient, one withdrawal). Four patients in the outpatient group were admitted before12 hours for suspected labor and rupture of membranes, and 19 in the inpatient group had the device removed before 12 hours. The proportion of participants with hospital stays longer than 48 hours was lower in the outpatient group compared with the inpatient group (89 [53%] vs 152 [89%], relative risk [RR] 0.60, 95% CI 0.52-0.70). Patients in the outpatient group had a shorter total length of stay and time from admission to active labor. They were more likely to have a vaginal delivery within 24 hours of admission and were less likely to receive analgesics during ripening. Route of delivery and other maternal and neonatal outcomes were not significantly different between groups.Conclusion: Outpatient cervical ripening with a cervical osmotic dilator decreased hospital stay compared with inpatient ripening, without significant adverse outcomes.Funding Source: Medicem Technology s.r.o., Czech Republic.Clinical Trial Registration: ClinicalTrials.gov, NCT03665688. [ABSTRACT FROM AUTHOR]

We present a general technique to assess and remove unwanted contributions from closely spaced features in spectra acquired using Auger-photoelectron coincidence spectroscopy. We use the Ag 3d[sub 5/2] and 3d[sub 3/2] core levels and their associated core valence-valence Auger decays, the Ag M[sub 5]VV and M[sub 4]VV Auger lines, to demonstrate this technique. Ag M[sub 5]VV and M[sub 4]VV Auger spectra were obtained in coincidence with 3d[sub 5/2] and 3d[sub 3/2] core photoelectrons, respectively. We have also measured the 3d[sub 5/2] and 3d[sub 3/2] core level spectra in coincidence with M[sub 5]VV and M[sub 4]VV Auger electrons. In the coincidence spectra, the contribution from the spin-orbit partner is considerably reduced but, in general, not eliminated. However, by measuring all four coincidence spectra, enough information is obtained to unambiguously assess and remove the unwanted contributions and thus determine the intrinsic line shape of the M[sub 5]VV and M[sub 4]VV Auger lines. As a cross-check of this subtraction technique, we find that the intrinsic M[sub 5]VV and M[sub 4]VV line shapes give an excellent account of the conventional, noncoincidence Ag M[sub 4,5]VV spectrum with the expected 6:4 ratio. The correction technique described here can be applied to a large number of systems where the close separation of core lines produces additional spectral features in the coincidence measurements of their associated Auger spectra. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetic, transport, and electronic properties of ultrathin epitaxial La1-xSrxMnO3 (LSMO) films at near half doping (x = 0.47, 0.50, and 0.55), grown under different misfit strains on SrTiO3(001) and La0.18Sr0.82Al0.59Ta0.41O3(001) (LSAT) substrates, are investigated. We find that all films exhibit metallic behavior below the magnetic critical temperature, while the magnetic properties change markedly with both doping and strain. However, while increased doping favors antiferromagnetic ordering, strain is the driving mechanism for the change in the magnetic properties, where with increasing tensile strain the magnetic ground state changes from ferromagnetic to antiferromagnetic at a critical lattice misfit threshold of about -1%. The bulk magnetometry data are confirmed by x-ray magnetic circular dichroism spectroscopy, while x-ray magnetic linear dichroism measured at room temperature demonstrates a progressive change in the orbital occupancy with increasing misfit strain from out of plane to in-plane, leading to a preferred antiferromagnetic metallic state at larger tensile strains. [ABSTRACT FROM AUTHOR]

The magnetic properties of iron-doped cobalt ferrite (Co1-xFe2+xO4) (001) thin films grown epitaxially on MgO (001) substrates are investigated by superconducting quantum interference device magnetometry and soft x-ray magnetic linear and circular dichroisms. All Co1-xFe2+xO4 (0.01 ⩽ × ⩽ 0.63) samples have out-of-plane magnetic easy axes and large coercive fields, unlike Fe3O4, due to a large Co2+ orbital moment. The magnetic moments for those samples are significantly reduced from their bulk values; however, as x increases, the magnetic moments tend nearer to their bulk values and increase more rapidly as x approaches 1. This reduction in magnetic moment is attributed to spin canting among the Co2+ cations, owing to a small in-plane tensile strain in the film and to an increased antiferromagnetic alignment among all the cations caused by a partially inverse spinel cubic structure and the likely presence of antiphase boundaries. Our results show that small changes in stoichiometry can lead to significant changes in the magnetic moment of Co1-xFe2+xO4, especially at large values of x. [ABSTRACT FROM AUTHOR]

Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomicspecific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. The results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value. [ABSTRACT FROM AUTHOR]

An in-plane vectorial analysis of the magnetization of thin magnetic films is presented. Longitudinal soft x-ray resonant magnetic reflectivity curves display characteristic nodes where the longitudinal scattering component is suppressed by x-ray interference. The transverse magnetic component can be effectively retrieved at these nodal points, despite the use of circular polarization and longitudinal scattering geometry. Using a single geometric configuration, transverse and longitudinal magnetic hysteresis loops can be clearly separated. Calculations based on a Stoner–Wohlfarth model satisfactorily describe both loops. Therefore, this method presents a viable alternative to standard vectorial analysis techniques, with the additional benefit of element specificity. [ABSTRACT FROM AUTHOR]

Using the surface, interface, and element specificity of x-ray resonant magnetic scattering in combination with x-ray magnetic circular dichroism, we have spatially resolved the polarization, and hence the spin accumulation in Mn high susceptibility material in close proximity to a ferromagnetic layer. The magnetic polarization of Mn and Cu 3d electrons in paramagnetic CuMn layers is detected in a Co/Cu(x)/CuMn structure for varying copper layer thicknesses (x). The size of the Mn and Cu L2–3-edge dichroism shows a decrease in the polarization for increasing copper thickness indicating the dominant interfacial nature of the Cu and Mn spin polarization. The Mn polarization appears to be much higher than that of Cu. [ABSTRACT FROM AUTHOR]

Annealing is necessary to achieve giant tunneling magnetoresistance (TMR) values in sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). In this study three complementary techniques were used to study the resulting changes in junction microstructure. The as-deposited TMR was modest, 5%, but rose to 101% after annealing at 325 °C for 1 h, corresponding to the tunneling spin polarization rising from 16% to 58%. Soft x-ray resonant magnetic scattering showed a roughening of the magnetic interfaces of the MTJ free layer, confirmed by transmission electron microscopy, which also showed the changes in the CoFeB and MgO to a lattice-matched polycrystalline form. [ABSTRACT FROM AUTHOR]

Self-assembled arrays of nanospheres have been used to pattern a Co/Pt multilayer into nanopillars. On top of this has been deposited a Co/Ru multilayer, which is antiferromagnetically coupled. The nanopillars introduce a known structural and magnetic lateral modulation into the multilayer. Soft x-ray magnetic scattering was used to observe the interference patterned from the patterned substrate. This has allowed us to show how the magnetic roughness correlates with the structural roughness and obtain selective magnetometry of the various magnetic elements. [ABSTRACT FROM AUTHOR]

The in-plane magnetic properties of Co0.7Fe0.3 films sputtered onto Al0.1Ga0.9As and Al0.1Ga0.9As/GaAs epilayers are consistent with a strongly oriented bcc crystal structure with clean metal-semiconductor interfaces. However, the interface induced uniaxial magnetic anisotropy is oriented along one of the in-plane <100>, rather than <110>, as is the case in molecular beam epitaxy—grown films. Resonant x-ray measurements show interfacial magnetic disorder in films on Al0.1Ga0.9As, which accounts for the difference in magnetic anisotropy behavior between samples on Al0.1Ga0.9As and Al0.1Ga0.9As/GaAs epilayer substrates, and which may have significant consequences for the spin-injection efficiency across such interfaces. [ABSTRACT FROM AUTHOR]

We present experimental techniques to measure magnetization precession of individual layers in a “spin-valve” trilayer. Precessional motions of individual Ni81Fe19 and Co93Zr7 layers have been separated in Ni81Fe19/Cu/Co93Zr7 using ±45 ps time-resolved x-ray magnetic circular dichroism (tr-XMCD) at Fe and Co edges. We compare the efficacy of two experimental configurations in this paper. Pulsed-field tr-XMCD measurements in reflectivity are compared with resonant-field tr-XMCD measurements in transmission. Despite the order of magnitude larger angles of precession excited in pulsed-field reflectivity measurements, data quality is found to be superior in resonant-field transmission measurements. Relative roles of sample preparation and timing jitter in the different techniques are discussed. [ABSTRACT FROM AUTHOR]

Co2MnSi thin films were grown on Al2O3 sa planed and GaAs (001) substrates and on thin silicon nitride windows using pulsed laser deposition. Angle-dependent magneto-optic Kerr effect measurements reveal both a uniaxial and a fourfold magnetocrystalline anisotropy for films grown on GaAs (001). X-ray magnetic circular dichroism spectra were measured at the L2,3 edges of the thin films as a function of aluminum cap layer thickness, and transmission mode L2,3 x-ray absorption through a 1000-Å Co2MnSi film grown on a silicon nitride membrane were measured, indicating that deviations from metalliclike spectra are likely due oxidation or contamination. Element-specific moments for Co and Mn were calculated from the X-ray magnetic circular dichroism data of a nonoxidized film. [ABSTRACT FROM AUTHOR]

Here we demonstrate an experimental observation of GHz-scale spin dynamics resolved to sublattice octahedral (Oh) tetrahedral (Td) sites in a spinel ferrimagnet, in this case a Mn-ferrite thin film. X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) are used, in combination with multiplet calculations, to uniquely identify the spectral signature from Mn2+ and Fe2+,3+ on Oh and Td lattice sites. With the sample under //excitation, the spin alignment of the sublattices is tracked with time-resolved XMCD (TR-XMCD). The spin alignment of the sublattices is mostly antiferromagnetic. The phase difference between the Oh Fe2+ [Oh Fe3+] and Td Mn2+ sites is 181.2 ± 3.8° [183.3° ± 3.7°] at 150 K and 186.6 ± 2.2° [182.0° ± 2.2°] at 300 K. Such direct measurement of the dynamic coupling, exchange stiffness, and damping enabled by TR-XMCD across sublattices will be essential for optimizing the development of future-generation microwave devices. [ABSTRACT FROM AUTHOR]

Discovering new antiferromagnetic (AF) compounds is at the forefront of developing future spintronic devices without fringing magnetic fields. The AF gapless semiconducting D03 phase of V3 A1 was successfully synthesized via arc-melting and annealing. The AF properties were established through synchrotron measurements of the atom-specific magnetic moments, where the magnetic dichroism reveals large and oppositely oriented moments on individual V atoms. Density functional theory calculations confirmed the stability of a type G antiferromagnetism involving only two-thirds of the V atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray diffraction, and transport measurements also support the antiferromagnetism. This archetypal gapless semiconductor may be considered as a cornerstone for future spintronic devices containing AF elements. [ABSTRACT FROM AUTHOR]

The article looks at a study that investigates symmetry breaking of the magnetic vortex state in nanoscopic ferromagnetic elements before annihilation. Topics discussed include properties of solitons undergoing structural breakdown, destabilization of the soliton through Zeeman and demagnetization interaction, and identification of the core polarity through the asymmetric states of elements.

To address the amount of disorder and interface diffusion induced by annealing, all-Heusler multilayer structures, consisting of ferromagnetic Co2MnGe and nonmagnetic Rh2CuSn layers of varying thicknesses, have been investigated by means of hard x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism. We find evidence for a 4 Å thick magnetically dead layer that, together with the identified interlayer diffusion, are likely reasons for the unexpectedly small magnetoresistance found for current-perpendicular-to-plane giant magnetoresistance devices based on this all-Heusler system. We find that diffusion begins already at comparably low temperatures between 200 and 250°C, where Mn appears to be most prone to diffusion. [ABSTRACT FROM AUTHOR]

Nanoislands of α'-FeRh were formed by the deposition of a 10 nm film onto (0 0 1)-MgO and observed by atomic force microscopy. This island-like architecture results in stabilized ferromagnetic (FM) ordering at low temperatures as noted by asymmetry in the x-ray diffraction peaks, a magnetostructural transition with a large magnetic background signal, and broad thermal hysteresis. The combination of structural and magnetic results suggest that the crystallographic arrangement of the FeRh nanoislands consists of a gradient of lattice parameters where there is a compressed inner region of lower lattice parameter values (attributed to antiferromagnetic ordering) which gradually relaxes outward to a region of larger lattice parameters (attributed to a retained FM ordering). The impact of this configuration on magnetostructural transformation is discussed in the context of classical nucleation theory. [ABSTRACT FROM AUTHOR]

The effect of film thickness on the magnetic properties of ultrathin Fe-doped cobalt ferrite (Co1-xFe2+xO4) grown on MgO (001) substrates is investigated by superconducting quantum interference device magnetometry and x-ray magnetic linear dichroism, while the distribution of the Co2+ cations between the octahedral and tetrahedral lattice sites is studied with x-ray absorption spectroscopy. For films thinner than 10 nm, there is a large enhancement of the magnetic moment; conversely, the remanent magnetization and coercive fields both decrease, while the magnetic spin axes of all the cations become less aligned with the [001] crystal direction. In particular, at 300 K the coercive fields of the thinnest films vanish. The spectroscopy data show that no changes occur in the cation distribution as a function of film thickness, ruling this out as the origin of the enhanced magnetic moment. However, the magnetic measurements all support the possibility that these ultrathin Fe-doped CoFe2O4 films are transitioning into a superparamagnetic state, as has been seen in ultrathin Fe3O4. A weakening of the magnetic interactions at the antiphase boundaries, leading to magnetically independent domains within the film, could explain the enhanced magnetic moment in ultrathin Fe-doped CoFe2O4 and the onset of superparamagnetism at room temperature. [ABSTRACT FROM AUTHOR]

The transition between Kondo and Coulomb blockade effects in discontinuous double magnetic tunnel junctions is explored as a function of the size of the CoPt magnetic clusters embedded between AlOx mnnel barriers. A gradual competition between cotunneling enhancement of the tunneling magnetoresistance (TMR) and the TMR suppression due to the Kondo effect has been found in these junctions, with both effects having been found to coexist even in the same sample. It is possible to tune between these two states with temperature (at a temperature far below the cluster blocking temperature). In addition, when further decreasing the size of the CoPt clusters, another gradual transition between the Kondo effect and direct tunneling between the electrodes takes place. This second transition shows that the spin-flip processes found in junctions with impurities in the barrier are in fact due to the Kondo effect. A simple theoretical model able to account for these experimental results is proposed. [ABSTRACT FROM AUTHOR]

Chromium-doped gallium sesquiselenide, Cr:Ga2Se3, is a member of a new class of dilute magnetic semiconductors exploiting intrinsic vacancies in the host material. The correlation among room-temperature ferromagnetism, surface morphology, electronic structure, chromium concentration, and local chemical and structural environments in Cr:Ga2Se3 films grown epitaxially on silicon is investigated with magnetometry, scanning tunneling microscopy, photoemission spectroscopy, and x-ray absorption spectroscopy. Inclusion of a few percent chromium in Ga2Se3 results in laminar, semiconducting films that are ferromagnetic at room temperature with a magnetic moment ⩾4μB/Cr. The intrinsic-vacancy structure of defected-zinc-blende β-Ga2Se3 enables Cr incorporation in a locally octahedral site without disrupting long-range order, determined by x-ray absorption spectroscopy, as well as strong overlap between Cr 3d states and the Se 4p states lining the intrinsic-vacancy rows, observed with photoemission. The highest magnetic moment per Cr is observed near the solubility limit of roughly one Cr per three vacancies. At higher Cr concentrations, islanded, metallic films result, with a magnetic moment that depends strongly on surface morphology. The effective valence is Cr3+ in laminar films, with introduction of Cr0 upon islanding. A mechanism is proposed for laminar films whereby ordered intrinsic vacancies mediate ferromagnetism. [ABSTRACT FROM AUTHOR]

The electronic, magnetic and transport properties of iron-doped cobalt ferrite (Co1-xFe2+xO4) thin films grown epitaxially on MgO (001) substrates are investigated by soft x-ray absorption and photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, superconducting quantum interference device magnetometry, and resistivity measurements. The crystal structure for Co1-xFe2+xO4 is determined to be nearly inverse spinel, with the degree of inversion increasing for increased doping until it becomes fully inverse spinel for Fe3O4. The doped iron cations have a valency of 2+ and reside solely on octahedral sites, which allows for conduction owing to hopping between Fe2+ and Fe3+ octahedral cations. The addition of Fe2+ cations increases the electron density of states near the Fermi energy, shifting the Fermi level from 0.75 to 0 eV with respect to the top of the valence band, as the doping increases from x = 0.01 to 1. This change in electronic structure results in a change in resistivity by over two orders of magnitude. In contrast, the magnetic properties of CoFe2O4 thin films, characterized by a significantly reduced saturation magnetization compared to the bulk and large magnetic anisotropies, are affected less significantly by doping in the range from 0 to 0.63. These results show that Co1-xFe2+xO4 has tunable electronic properties while maintaining magnetic properties similar to CoFe2O4. [ABSTRACT FROM AUTHOR]

We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>104) and spot size (4×4 μm2) at the sample position despite being exposed to more than 2.15 kW of undulator radiation and a maximum power density on the optics of more than 0.9 W/mm2. Ray tracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulator’s central cone, which contains the usable photons but is considerably smaller than the angular power distribution. [ABSTRACT FROM AUTHOR]

O1s and Mn2p near-edge X-ray absorption spectroscopy on La1-xSr1+xMnO4 (0 ≤x ≤0.5) single crystals shows that Sr doping does not only provide holes to the system but also induces a continuous transfer of electrons from out-of-plane d3z2-r2 to in-plane d3x2-r2/d3y2-r2 orbitals. Furthermore, a non-vanishing electron occupation of in-plane dx2-y2 and out-of-plane d3z2-r2 orbitals is observed up to relatively high doping contents. These findings demonstrate that the energy difference between all these orbital types has to be very small and manifest that the orbital degree of freedom is determined not just by crystal field effects but also by orbital coupling. Moreover, the doping-dependent transfer of spectral weight observed in the current data identifies La1-xSr1+xMnO4 as a charge-transfer insulator. [ABSTRACT FROM AUTHOR]

A hybrid mode matching (MM)-finite element (FE) technique is presented, with application to the analysis of waveguide components and inductive frequency selective surfaces (FSSs). The proposed hybrid approach combines the computational efficiency of the MM analysis with the versatility and flexibility of the FE method. One of the key features of the present formulation is the expansion of transverse electric and magnetic fields by using tangential vector edge elements (TVEEs), which guarantee spurious-free solutions; indeed, this property is very important for an accurate numerical determination of the modal eigenvalues. FSSs, realized by periodically perforating thick metallic screens with arbitrarily shaped apertures, are analyzed by expanding the electromagnetic fields in the free-space region through a complete set of Floquet modes that allows us to reduce the analysis to the single periodicity cell; modes inside apertures are determined through a FEM procedure. A spectral criterion to determine the correct ratio between the number of FEM-reconstructed and analytically derived modes is adopted. Samples of numerical results are shown in order to check both the effectiveness and the accuracy of the proposed procedure. [ABSTRACT FROM AUTHOR]

We present time- and element-resolved measurements of the magnetization dynamics in a ferromagnetic trilayer structure. A pump-probe scheme was utilized with a microwave magnetic excitation field phase-locked to the photon bunches and x-ray magnetic circular dichroism in transmission geometry. Using a relatively large photon bunch length with a full width at half maximum of 650 ps, the precessional motion of the magnetization was resolved up to frequencies of 2.5 GHz, thereby enabling sampling at frequencies significantly above the inverse bunch length. By simulating the experimental data with a numerical model based on a forced harmonic oscillator, we obtain good correlation between the two. The model, which includes timing jitter analysis, is used to predict the accessible frequency range of x-ray detected ferromagnetic resonance. [ABSTRACT FROM AUTHOR]

It is common to find a thin (∼0.5 nm) layer of Mg deposited prior to the MgO tunnel barrier in crystalline CoFe(B)/MgO/CoFe(B) magnetic tunnel junctions, due to the improved device performance that results. However, despite their common usage, the reasons why such layers are effective are unclear. We use structures that model the lower electrode of such devices to show that a suitably thick Mg insert layer enhances the crystal quality of both MgO and CoFe(B), permits interfacial oxides to reduce back to a metallic ferromagnetic state, and hence improves magnetic switching of the CoFe(B) electrode, properties which are inextricably linked to device performance. [ABSTRACT FROM AUTHOR]

We have studied the effect of annealing on the interface magnetization in a CoFeB/MgO structure which models the lower electrode in a magnetic tunnel junction device. We find that MgO deposition causes Fe to diffuse toward the CoFeB/MgO interface, where it preferentially bonds with oxygen to form a Fe-O-rich interfacial region with reduced magnetization. After annealing at 375 °C the compositional inhomogeneity remains; Fe is reduced back to a ferromagnetic metallic state and the full interfacial magnetization is regained. [ABSTRACT FROM AUTHOR]

The third international workshop on hard X-ray photoelectron spectroscopy (HAXPES 2009) was held at Brookhaven National Laboratory, Upton, New York, from May 20-22, 2009. This three-day workshop brought together approximately 100 scientists from 14 countries to discuss progress and future prospects for this rapidly developing field of research. The conference was sponsored by the National Synchrotron Light Source, the National Synchrotron Light Source-II Project, Brookhaven National Laboratory Condensed Matter Physics and Materials Science Department, and the National Institute of Standards and Technology. [ABSTRACT FROM AUTHOR]

Surface structural effects accompanying the antiferromagnetic-ferromagnetic magnetostructral transition of epitaxial FeRh thin films were investigated by grazing incidence x-ray scattering. Measurement of the film lattice parameters and variation of x-ray incident angles allow observation of the transition character on scales ranging from a few nm to the total through-thickness of the film. Out-of-plane lattice measurements confirm that the ferromagnetic phase nucleates from the surface during the heating process and is retained at the surface below the transition temperature during the cooling process. These results suggest that surface strain relief fosters nucleation of the ferromagnetic phase. [ABSTRACT FROM AUTHOR]

Single dusting layers of size-selected Co nanoclusters (NCs) of sizes ranging from 1.5–5.5 nm have been deposited by a gas-phase aggregation method in ultrahigh vacuum, and embedded within a NiFe matrix. Magnetic hysteresis loops have been obtained using soft x-ray magnetic circular dichroism, which shows that these Co NCs embedded in NiFe exhibit room temperature ferromagnetism with identical coercivity to the surrounding NiFe film. The strong local exchange field at the interface between NiFe and Co NCs, combined with the magnetic anisotropy of the NiFe film, allows stabilization of NC ferromagnetism which persists to room temperature. [ABSTRACT FROM AUTHOR]

We have studied the reversal of the bulk and interfacial magnetizations of the free layer of a spin valve using soft x-ray resonant magnetic scattering. By dusting the interface of the NiFe free layer with a few angströms of Co, we were able to distinguish between the interfacial and bulk magnetisms by tuning the x-ray photon energy. We measured hysteresis loops of reflected x-ray intensity at selected points in reciprocal space. We find no difference in the switching fields, showing that in transition metal ferromagnets, the exchange interactions are sufficiently strong to prevent a separate interfacial coercivity from arising. [ABSTRACT FROM AUTHOR]

The authors report on the use of a Co/Pt multilayer, which exhibits strong perpendicular magnetic anisotropy, to magnetostatically imprint a domain pattern onto a 50 Å thick Permalloy layer. Element specific soft x-ray magnetic scattering experiments were then performed so as to be sensitive to the magnetic structure of the Permalloy only. Off-specular magnetic satellite peaks, corresponding to a periodic domain stripe width of 270 nm, were observed, confirmed by magnetic force microscopy and micromagnetic modeling. Thus the authors have exploited the element specificity of soft x-ray scattering to discern the purely magnetic correlations in a structurally flat Permalloy film. [ABSTRACT FROM AUTHOR]

Fe ions of dose 5×1016 cm-2 were implanted at 200 keV into a-plane ZnO epitaxial films. The epitaxial quality of the postannealed samples was verified by x-ray diffraction ω-rocking curves and φ scans, whereas x-ray absorption spectroscopy identified the presence of both Fe2+ and Fe3+ ions, as well as changes in their relative concentration during postannealing. Superconducting quantum interference device measurements show that the as-implanted and postannealed films are ferromagnetic at room temperature. The saturation magnetization reduces during annealing possibly due to the decrease in the number of oxygen vacancies. [ABSTRACT FROM AUTHOR]

We report the results of soft x-ray resonant magnetic scattering experiments conducted on Co/Ru magnetic multilayers patterned into a reflection grating. Sample magnetization dependent scans of the in-plane wave vector transfer were performed to probe the relationship between the lateral physical and magnetic structures. Different Fourier components were found to dominate the sum and difference of these spectra, corresponding to different lateral wave forms for the structure-structure and structure-magnetism correlations. [ABSTRACT FROM AUTHOR]

Tensile strain along the cR axis in epitaxial VO2 films raises the temperature of the metal insulator transition and is expected to stabilize the intermediate monoclinic M2 phase. We employ surface-sensitive x-ray spectroscopy to distinguish from the TiO2 substrate and identify the phases of VO2 as a function of temperature in epitaxial VO2/TiO2 thin films with well-defined biaxial strain. Although qualitatively similar to our Landau-Ginzburg theory predicted phase diagrams, the M2 phase is stabilized by nearly an order of magnitude more strain than expected for the measured temperature window. Our results reveal that the elongation of the cR axis is insufficient for describing the transition pathway of VO2 epitaxial films and that a strain induced increase of electron correlation effects must be considered. [ABSTRACT FROM AUTHOR]

The distribution of cations in Fe-doped cobalt ferrite (Co1-xFe2+xO4) is investigated as a function of epitaxial strain through x-ray absorption measurements of samples grown on SrTiO3, MgO, and CoCr2O4-buffered MgAl2O4 (001). In agreement with recent theoretical calculations, compressive (tensile) strain results in the films having a larger (smaller) degree of cation inversion for iron doping levels up to x = 0.62. Measurements of the resistivity further conclude that the degree of cation inversion has a direct effect on the size of the bandgap for stoichiometric CoFe2O4, an effect that is reduced as the iron doping level is increased. [ABSTRACT FROM AUTHOR]