X-ray Resonant Magnetic Scattering Research Articles

Chiral structures of electric polarization vectors quantified by X-ray resonant scattering

Resonant elastic X-ray scattering (REXS) offers a unique tool to investigate solid-state systems providing spatial knowledge from diffraction combined with electronic information through the enhanced absorption process, allowing the probing of magnetic, charge, spin, and orbital degrees of spatial order together with electronic structure. A new promising application of REXS is to elucidate the chiral structure of electrical polarization emergent in a ferroelectric oxide superlattice in which the polarization vectors in the REXS amplitude are implicitly described through an anisotropic tensor corresponding to the quadrupole moment. Here, we present a detailed theoretical framework and analysis to quantitatively analyze the experimental results of Ti L-edge REXS of a polar vortex array formed in a PbTiO3/SrTiO3 superlattice. Based on this theoretical framework, REXS for polar chiral structures can become a useful tool similar to x-ray resonant magnetic scattering (XRMS), enabling a comprehensive study of both electric and magnetic REXS on the chiral structures.

Depth-dependent Spin Polarizations Induced in Cu(001) and Cu(111) Layers of Co/Cu Multilayers Determined by Resonant X-ray Magnetic Scattering at the Cu K Absorption Edge

Co/Cu(001) multilayers were prepared by sputtering and the depth-dependent spin polarization induced in the conduction electrons of the Cu layers was investigated by resonant X-ray magnetic scatter...

Magnetic ordering and structural distortion in a PrFeAsO single crystal studied by neutron and x-ray scattering.

We report the magnetic ordering and structural distortion in PrFeAsO crystals, the basis compound for one of the oxypnictide superconductors, using high-resolution x-ray diffraction, neutron diffraction, and x-ray resonant magnetic scattering (XRMS). We find the structural tetragonal-to-orthorhombic phase transition at , the AFM phase transition of the Fe moments at , and the Pr AFM phase transition at . Combined high-resolution neutron diffraction and XRMS show unambiguously that the Pr moments point parallel to the longer orthorhombic axis and order antiferromagnetically along the axis but ferromagnetically along the and directions in the stripelike AFM order. The temperature-dependent magnetic order parameter of the Pr moments shows no evidence for a reorientation of moments.

Indirect Magnetic Coupling through the Nonmagnetic Au Layer in the Fe/Au/CoO Trilayer Investigated by Resonant X-ray Magnetic Scattering at the Co K Absorption Edge

Indirect magnetic coupling between a ferromagnetic Fe layer and an antiferromagnetic CoO layer through a nonmagnetic Au layer was investigated with resonant X-ray magnetic scattering (RXMS) measure...

Modeling inter-particle magnetic correlations in magnetite nanoparticle assemblies using x-ray magnetic scattering data

Magnetic nanoparticles are increasingly used in nanotechnologies and biomedical applications, such as drug targeting, MRI, bio-separation. Magnetite (Fe3O4) nanoparticles stand to be effective in these roles due to the non-toxic nature of magnetite and its ease of manufacture. To be more effective in these applications, a greater understanding of the magnetic behavior of a collection of magnetite nanoparticles is needed. This research seeks to discover the local magnetic ordering of ensembles of magnetite nanoparticles occurring under various external fields. To complete this study, we use x-ray resonant magnetic scattering (XRMS). Here we discuss the modeling of the magnetic scattering data using a one-dimensional chain of nanoparticles with a mix of ferromagnetic, anti-ferromagnetic, and random orders. By fitting the model to the experimental data, we extracted information about the magnetic correlations in the nanoparticle assembly.

Layer-Resolved Vector Magnetization Processes of Ferrimagnetic Fe1/Au/Fe2/Au(001) Multilayer by Resonant X-ray Magnetic Scattering at the Fe K Absorption Edge

Layer-resolved vector magnetization processes were investigated for Fe layers in a ferrimagnetic Fe1/Au/Fe2/Au(001) multilayer. The magnetic hysteresis curves of resonant X-ray magnetic scattering ...

Unraveling Nanoscale Magnetic Ordering in Fe3O4 Nanoparticle Assemblies via X-rays

Understanding the correlations between magnetic nanoparticles is important for nanotechnologies, such as high-density magnetic recording and biomedical applications, where functionalized magnetic particles are used as contrast agents and for drug delivery. The ability to control the magnetic state of individual particles depends on the good knowledge of the magnetic correlations between particles when assembled. Inaccessible via standard magnetometry techniques, nanoscale magnetic ordering in self-assemblies of Fe3O4 nanoparticles is here unveiled via X-ray resonant magnetic scattering (XRMS). Measured throughout the magnetization process, the XRMS signal reveals size-dependent inter-particle magnetic correlations. Smaller (5 nm) particles show little magnetic correlations, even when packed close together, yielding to magnetic disorder in the absence of an external field, i.e., superparamagnetism. In contrast, larger (11 nm) particles tend to be more strongly correlated, yielding a mix of magnetic orders including ferromagnetic and anti-ferromagnetic orders. These magnetic correlations are present even when the particles are sparsely distributed.

Chirality in Magnetic Multilayers Probed by the Symmetry and the Amplitude of Dichroism in X-Ray Resonant Magnetic Scattering.

Chirality in condensed matter has recently become a topic of the utmost importance because of its significant role in the understanding and mastering of a large variety of new fundamental physical mechanisms. Versatile experimental approaches, capable to reveal easily the exact winding of order parameters, are therefore essential. Here we report x-ray resonant magnetic scattering as a straightforward tool to reveal directly the properties of chiral magnetic systems. We show that it can straightforwardly and unambiguously determine the main characteristics of chiral magnetic distributions: i.e., its chiral nature, the quantitative winding sense (clockwise or counterclockwise), and its type, i.e., Néel [cycloidal] or Bloch [helical]. This method is model independent, does not require apriori knowledge of the magnetic parameters, and can be applied to any system with magnetic domains ranging from a few nanometers (wavelength limited) to several microns. By using prototypical multilayers with tailored magnetic chiralities driven by spin-orbit-related effects at Co|Pt interfaces, we illustrate the strength of this method.

Perpendicular Magnetic Anisotropy and Induced Magnetic Structures of Pt Layers in the Fe/Pt Multilayers Investigated by Resonant X-ray Magnetic Scattering

Depth distribution of the magnetization induced in the paramagnetic Pt layers of Fe/Pt multilayers was investigated by resonant X-ray magnetic scattering (RXMS) near the Pt L3 absorption edge. Two samples with different perpendicular magnetic anisotropy (PMA) were chosen for RXMS measurements. The magnetic depth profile of the Pt layer was determined in the magnetic saturation state of the Fe magnetization with the sample of weak PMA. The magnetization process of the Pt layer was investigated with the sample of moderate PMA. It is found that the Pt atoms near the interface region have a perpendicular component of the induced magnetization even in the saturation state of the Fe magnetization, suggesting that the PMA of Fe/Pt multilayers originates from the Pt atoms near the interface region. Concerning the magnetization process, the induced Pt magnetization is not proportional to the Fe magnetization. This implies a complicated magnetizing mechanism of the Pt layer by the Fe magnetization.

Employing soft x-ray resonant magnetic scattering to study domain sizes and anisotropy in Co/Pd multilayers

It is demonstrated that the magnetic diffraction pattern of the isotropic disordered maze pattern is well described utilizing a gamma distribution of domain sizes in a one-dimensional model. From the analysis, the mean domain size and the shape parameter of the distribution are obtained. The model reveals an average domain size that is significantly different from the value that is determined from the peak position of the structure factor in reciprocal space. As a proof of principle, a wedge-shaped $({\mathrm{Co}}_{t\AA{}}/{\mathrm{Pd}}_{10\AA{}}{)}_{8}$ multilayer film, that covers the thickness range of the spin-reorientation transition, has been used. By means of soft x-ray resonant magnetic scattering (XRMS) and imaging techniques the thickness-driven evolution of the magnetic properties of the cobalt layers is explored. It is shown that minute changes of the domain pattern concerning domain size and geometry can be investigated and analyzed due to the high sensitivity and lateral resolution of the XRMS technique. The latter allows for the determination of the magnetic anisotropies of the cobalt layers within a thickness range of a few angstroms.

Atomic structure of the i-R-Cd quasicrystals and consequences for magnetism

We report on the six-dimensional (6D) structural refinement of three members of the i-$R$-Cd quasicrystals ($R$ = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-${\mathrm{YbCd}}_{5.7}$ quasicrystal. However, our refinements suggest that the $R$ occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-$R$-Cd series and i-${\mathrm{ScZn}}_{7.33}$, and their differences with i-${\mathrm{YbCd}}_{5.7}$ and i-${\mathrm{Ca}}_{15}{\mathrm{Cd}}_{85}$, indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show from x-ray resonant magnetic scattering (XRMS) measurements on a set of closely related ${\mathrm{Tb}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{Cd}}_{6}$ 1/1 approximants that the dilution of the magnetic $R$ ions on the icosahedron within the Tsai-type cluster by nonmagnetic Y disrupts the commensurate magnetic ordering in the approximant phase.

Composition dependence of charge and magnetic length scales in mixed valence manganite thin films.

Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1−yPry)1−xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1−xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.

Magnetic properties ofGdT2Zn20(T=Fe, Co) investigated by x-ray diffraction and spectroscopy

We investigate the magnetic and electronic properties of the Gd$T_2$Zn$_{20}$ ($T$ = Fe and Co) compounds using X-ray resonant magnetic scattering (XRMS), X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) techniques. The XRMS measurements reveal that the GdCo$_2$Zn$_{20}$ compound has a commensurate antiferromagnetic spin structure with a magnetic propagation vector $\vec{\tau}$ = $(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ below the N\'eel temperature ($T_N \sim$ 5.7 K). Only the Gd ions carry a magnetic moment forming an antiferromagnetic structure with magnetic representation $\Gamma_6$. For the ferromagnetic GdFe$_2$Zn$_{20}$ compound, an extensive investigation was performed at low temperature and under magnetic field using XANES and XMCD techniques. A strong XMCD signal of about 12.5 $\%$ and 9.7 $\%$ is observed below the Curie temperature ($T_C \sim$ 85 K) at the Gd-$L_2$ and $L_3$ edges, respectively. In addition, a small magnetic signal of about 0.06 $\%$ of the jump is recorded at the Zn $K$-edge suggesting that the Zn 4$p$ states are spin polarized by the Gd 5$d$ extended orbitals.

Magnetic polarization of Ir in underdoped nonsuperconductingEu(Fe0.94Ir0.06)2As2

Using polarized neutron diffraction and x-ray resonant magnetic scattering (XRMS) techniques, multiple phase transitions were revealed in an underdoped, non-superconducting Eu(Fe$_{1-x}$Ir$_{x}$)$_{2}$As$_{2}$ ($\mathit{x}$ = 0.06) single crystal. Compared with the parent compound EuFe$_{2}$As$_{2}$, the tetragonal-to-orthorhombic structural phase transition and the antiferromagnetic order of the Fe$^{2+}$ moments are significantly suppressed to $\mathit{T_{S}}$ = 111 (2) K and $\mathit{T_{N,Fe}}$= 85 (2) K by 6% Ir doping, respectively. In addition, the Eu$^{2+}$ spins order within the $\mathit{ab}$ plane in the A-type antiferromagnetic structure similar to the parent compound. However, the order temperature is evidently suppressed to $\mathit{T_{N,Eu}}$= 16.0 (5) K by Ir doping. Most strikingly, the XRMS measurements at the Ir $\mathit{L_{3}}$ edge demonstrates that the Ir 5$\mathit{d}$ states are also magnetically polarized, with the same propagation vector as the magnetic order of Fe. With $\mathit{T_{N,Ir}}$ = 12.0 (5) K, they feature a much lower onset temperature compared with $\mathit{T_{N,Fe}}$. Our observation suggests that the magnetism of the Eu sublattice has a considerable effect on the magnetic nature of the 5$\mathit{d}$ Ir dopant atoms and there exists a possible interplay between the localized Eu$^{2+}$ moments and the conduction $\mathit{d}$-electrons on the FeAs layers.

Importance ofXYanisotropy inSr2IrO4revealed by magnetic critical scattering experiments

The magnetic critical scattering in Sr$_2$IrO$_4$ has been characterized using X-ray resonant magnetic scattering (XRMS) both below and above the 3D antiferromagnetic ordering temperature, T$_{\text{N}}$. The order parameter critical exponent below T$_{\text{N}}$ is found to be \beta=0.195(4), in the range of the 2D XYh$_4$ universality class. Over an extended temperature range above T$_{\text{N}}$, the amplitude and correlation length of the intrinsic critical fluctuations are well described by the 2D Heisenberg model with XY anisotropy. This contrasts with an earlier study of the critical scattering over a more limited range of temperature which found agreement with the theory of the isotropic 2D Heisenberg quantum antiferromagnet, developed to describe the critical fluctuations of the conventional Mott insulator La$_2$CuO$_4$ and related systems. Our study therefore establishes the importance of XY anisotropy in the low-energy effective Hamiltonian of Sr$_2$IrO$_4$, the prototypical spin-orbit Mott insulator.

Induced Spin Polarization in the Au Layers of Fe/Au Multilayer in an Antiparallel Alignment State of Fe Magnetizations by Resonant X-ray Magnetic Scattering at the Au L3Absorption Edge

A double periodic Fe1/Au/Fe2/Au multilayer with different Fe thicknesses was epitaxially grown on the MgO(001) substrate to investigate the magnetic structure of the Au spin polarization in an antiparallel alignment state of the Fe magnetizations. The establishment of the antiparallel alignment state at zero applied field was confirmed from the comparison of the magnetization curve measurement and simulation in the applied field along the [110] direction of the MgO substrate. Existence of the Au spin polarization orthogonal to the applied magnetic field was confirmed with resonant X-ray magnetic scattering (RXMS) measurements near the Au L3 absorption edge. Analysis of the RXMS pattern indicated that the magnetic depth profile of the spin polarization in the interior region of the Au layer was approximated to a square-wave shape, which suggests a ferromagnetic nature of the Au spin polarization sandwiched by the Fe layers.

Depth Profile of Induced Magnetic Polarization in Cu Layers of Co/Cu(111) Metallic Superlattices by Resonant X-ray Magnetic Scattering at the Cu K Absorption Edge

We investigated induced spin polarization of 4p conduction electrons in Cu layers of antiferromagnetically (AFM) and ferromagnetically (FM) coupled Co/Cu(111) metallic superlattices by resonant X-ray magnetic scattering at the Cu K absorption edge. Magnetic reflectivity profiles of the two superlattices were measured in the magnetic saturation state with circularly polarized synchrotron radiation X-rays at 8985 eV. Depth profiles of the resonant magnetic scattering length of Cu, which corresponds to the induced spin polarization of Cu, were evaluated in the two Co/Cu superlattices by analyzing the observed magnetic reflectivity profiles. We demonstrated that the spin polarization induced in the Cu layer was distributed around the Co/Cu interfaces with an attenuation length of several A in both AFM and FM coupled superlattices. The uniform component, which exists in Au layers of Fe/Au(001) superlattices, was not found in the depth distribution of induced magnetic polarization in the Cu layers of Co/Cu(111)...

Site-specific RXMS study on the magnetic electron of magnetite

Magnetite Fe3O4 is the best known magnetic mineral for its attractive properties for various magnetic applications. The magnetic moments of Fe atoms show a collinear ferrimagnetic ordering between tetrahedral A and octahedral B sites in an inverse spinel structure with the chemical formula of [Fe3+]A[Fe2+Fe3+]BO4. The distribution of the Fe2+ and Fe3+ over A and B sites is determined by a delicate balance of the crystal field. The geometrical environment of 3d transition metals strongly affects the distribution and the energy state of magnetic electrons which contributes magnetic moments. The resonant x-ray magnetic scattering (RXMS) allows us to make site-selective structural analysis with respect to the magnetic electron. In order to clarify the behavior of the magnetic electrons in magnetite, we carried out the energy-dependent RXMS near Fe K edge. Depends on the observation related to 3d-4p electric transition to empty bands of unpaired electron, we studied the orbital interaction and the density of state of magnetic electrons in A site and B site of magnetite independently. RXMS intensity measurements were performed by using Rigaku AFC-5u four-circle diffractometers at BL-6C of Photon Factory. Circularly-polarized X-rays were produced by a transmitted-type phase retarder of diamond (111). According to the X-ray magnetic circular dichroism (XMCD) spectrum at the Fe K edge, 48 x-ray energies to perform RXMS measurement were selected. The magnetic form factors for various energies were calculated from the difference in diffraction intensities between left- and right-circular polarized measurements. By examining the energy dependence of the resonant magnetic peaks, the density of state of 3d magnetic electron of Fe were obtained for A and B site through the experimental analysis. In the presentation, the interrelationship between the site geometry and the magnetic electrons in terms of energy state will be discussed.

Magnetic electron density in Fe3O4 examined by RXMS at Fe K edge

"It is known that a difference-Fourier synthesis of the Fourier series provides a mean for the location of bonding electrons, by subtracting out the electron density of all atoms in the crystal structure. Here the Fourier technique in X-ray diffraction was applied to observe the magnetic electron density of magnetite Fe3O4. An asymmetrical ratio in the resonant X-ray magnetic scattering (RXMS) provides information on the magnetic moments, which can be estimated from an intensity difference between the right-handed and left-handed polarized X rays. The ratio is proportional to the real part of the product of the spin-contributed structure factor F(hkl) and the complex conjugation of charge-scattered F(hkl). Expanding the equations in difference–Fourier formalization, the spin density can be represented with the observed f""m of RXMS. Synchrotron RXMS experiments were performed at the PF-BL-6C beamline using an AFC-5u four-circle diffractometer. Through a diamond phase retarder the incident X rays were circularly polarized at the Fe K absorption edge, where a wavelength of λ = 1.7439 Å (E = 7.1094 keV) was selected within the pre-edge. A spherical crystal of 0.13 mm in diameter was mounted along the a3 axis with the glass fiber on rare-earth magnet and goniometer head. The intensity data of RXMS were collected for Bragg reflections up to 2θ = 1310. After crystal-structure refinements with scaling of the RXMS data, difference-Fourier syntheses were made in triclinic symmetry with a total of 165 reflections by using the software FRAXY. The syntheses are superior in examining the magnetic effect in the polarization difference and eliminating other effects such as charge scattering, experimental errors and the termination effect. The difference of magnetic electron density between left-handed and right-handed circular polarizations at E was estimated in the Fourier series of partially observed F(hkl). The magnetic electron density on Fourier maps will be discussed in the presentation."

Resonant X-ray magnetic scattering study of Ti-Mn-doped Ba ferrites

BaFe12O19 has M-type hexaferrite structure, giving strong uniaxial anisotropy of the magnetization along c axis. In doped BaTixMnxFe12-2xO19, the substitution of Fe3+ by a pair of Ti4+ and Mn2+ results in a weakening of the magnetic interactions due to the canting of magnetic moments. The crystal structure has a sequence of (Fe6O8) spinel and (BaFe6O11) hcp blocks, associated with five independent Fe sites: tetrahedral 4f1, bipyramidal 2b, and octahedral 2a, 4f2 and 12k sites. Single crystals synthesized by a flux method have cell dimensions of a = 5.8953(2) and c = 23.1887(8) Å and a = 5.9039(2) and c = 23.2047(8) Å for samples of x = 0.5 and 1.0, respectively. Each crystal was mounted with short glass fiber on rare-earth magnet and goniometer head. Conventional intensity measurements were made using a Rigaku AFC7 four-circle diffractometer with a graphite (002) monochromator for Mo Kα radiation. Site-occupancy experiments were performed by using a vertical-type four-circle diffractometer at PF-BL-10A. In this study the magnetic structure has been examined to use resonant X-ray magnetic scattering (RXMS) at the Fe K absorption edge in PF-BL-6C. Circularly polarized X rays produced by a diamond phase retarder were switched between right-handed (helicity=+1) and left-handed polarizations. An AFC-5u four-circle diffractometer was used in the geometry of horizontal scattering plane. Intensity measurements were made to collect as many as possible of Bragg reflections. Based on an asymmetrical ratio of the intensities between right- and left- handed circular polarizations, the intensity difference in the RXMS was estimated for each of reflections. A set of observed asymmetrical ratios was fitted to a model of spin orientation in crystal-structure calculations with the resonant magnetic scattering factors. A residual function in the least-squares fitting is useful to evaluate magnetic moments for individual sites, which is a multiplicity parameter refined in terms of atomic scattering factor. It gives a minimum in plot between site-multiplicity and residual function, assigning the multiplicity related to the canting of magnetic moment in the Fe sites. The magnetic structure obtained in this study is compared with those of M-type BaFe12O19 and BaTiCoFe10O19.