Advanced data analysis procedure for hard x-ray resonant magnetic reflectivity discussed for Pt thin film samples of various complexity

X-ray resonant magnetic reflectivity (XRMR) is a powerful method to determine the optical, structural and magnetic depth profiles of a variety of thin films. Here, we investigate samples of different complexity all measured at the Pt L$_3$ absorption edge to determine the optimal procedure for the analysis of the experimental XRMR curves, especially for nontrivial bi- and multilayer samples that include differently bonded Pt from layer to layer. The software tool ReMagX is used to fit these data and model the magnetooptic depth profiles based on a highly adaptable layer stack which is modified to be a more precise and physically consistent representation of the real multilayer system. Various fitting algorithms, iterative optimization approaches and a detailed analysis of the asymmetry ratio features as well as $\chi^2$ (goodness of fit) landscapes are utilized to improve the agreement between measurements and simulations. We present a step-by-step analysis procedure tailored to the Pt thin film systems to take advantage of the excellent magnetic sensitivity and depth resolution of XRMR.Comment: 16 pages, 14 figure

Resonant elastic X-ray scattering of antiferromagnetic superstructures in EuPtSi3_{3}

We report resonant elastic X-ray scattering (REXS) of long-range magnetic order in EuPtSi$_{\text{3}}$, combining different scattering geometries with full linear polarization analysis to unambiguously identify magnetic scattering contributions. At low temperatures, EuPtSi$_{\text{3}}$ stabilizes type A antiferromagnetism featuring various long-wavelength modulations. For magnetic fields applied in the hard magnetic basal plane, well-defined regimes of cycloidal, conical, and fan-like superstructures may be distinguished that encompass a pocket of commensurate type A order without superstructure. For magnetic field applied along the easy axis, the phase diagram comprises the cycloidal and conical superstructures only. Highlighting the power of polarized REXS, our results reveal a combination of magnetic phases that suggest a highly unusual competition between antiferromagnetic exchange interactions with Dzyaloshinsky--Moriya spin--orbit coupling of similar strength

Quantitative comparison of the magnetic proximity effect in Pt detected by XRMR and XMCD

X-ray resonant magnetic reflectivity (XRMR) allows for the simultaneous measurement of structural, optical and magnetooptic properties and depth profiles of a variety of thin film samples. However, a same-beamtime same-sample systematic quantitative comparison of the magnetic properties observed with XRMR and x-ray magnetic circular dichroism (XMCD) is still pending. Here, the XRMR results (Pt L$_{3}$ absorption edge) for the magnetic proximity effect in Pt deposited on the two different ferromagnetic materials Fe and Co$_{33}$Fe$_{67}$ are compared with quantitatively analyzed XMCD results. The obtained results are in very good quantitative agreement between the absorption-based (XMCD) and reflectivity-based (XRMR) techniques taking into account an ab initio calculated magnetooptic conversion factor for the XRMR analysis. Thus, it is shown that XRMR provides quantitative reliable spin depth profiles important for spintronic and spin caloritronic transport phenomena at this type of magnetic interfaces.Comment: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 118, 012407 (2021) and may be found at https://aip.scitation.org/doi/abs/10.1063/5.003258

Static magnetic proximity effect in Pt/NiFe2O4 and Pt/Fe bilayers investigated by x-ray resonant magnetic reflectivity

The spin polarization of Pt in Pt/NiFe2O4 and Pt/Fe bilayers is studied by interface-sensitive x-ray resonant magnetic reflectivity to investigate static magnetic proximity effects. The asymmetry ratio of the reflectivity was measured at the Pt L3 absorption edge using circular polarized x-rays for opposite directions of the magnetization at room temperature. The results of the 2% asymmetry ratio for Pt/Fe bilayers are independent of the Pt thickness between 1.8 and 20 nm. By comparison with ab initio calculations, the maximum magnetic moment per spin polarized Pt atom at the interface is determined to be $(0.6\pm0.1)\,\mu_{B}$ for Pt/Fe. For Pt/NiFe2O4 the asymmetry ratio drops below the sensitivity limit of $0.02\,\mu_{B}$ per Pt atom. Therefore, we conclude, that the longitudinal spin Seebeck effect recently observed in Pt/NiFe2O4 is not influenced by a proximity induced anomalous Nernst effect.Comment: 5 pages, 5 figure

Structurally assisted melting of excitonic correlations in 1T-TiSe2

The simultaneous condensation of electronic and structural degrees of freedom gives rise to new states of matter, including superconductivity and charge-density-wave formation. When exciting such a condensed system, it is commonly assumed that the ultrafast laser pulse disturbs primarily the electronic order, which in turn destabilizes the atomic structure. Contrary to this conception, we show here that structural destabilization of few atoms causes melting of the macroscopic ordered charge-density wave in 1T-TiSe2. Using ultrafast pump-probe non-resonant and resonant X-ray diffraction, we observe full suppression of the Se 4p orbital order and the atomic structure at excitation energies more than one order of magnitude below the suggested excitonic binding energy. Complete melting of the charge-density wave occurs 4-5 times faster than expected from a purely electronic charge-screening process, strongly suggesting a structurally assisted breakup of excitonic correlations. Our experimental data clarifies several questions on the intricate coupling between structural and electronic order in stabilizing the charge-density-wave in 1T-TiSe2. The results further show that electron-phonon-coupling can lead to different, energy dependent phase-transition pathways in condensed matter systems, opening new possibilities in the conception of non-equilibrium phenomena at the ultrafast scale.Comment: 19 pages, 4 figure

Hidden Charge Order in an Iron Oxide Square-Lattice Compound

Since the discovery of charge disproportionation in the FeO2 square-lattice compound Sr3Fe2O7 by Mössbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained “hidden” to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe K-edge resonant x-ray scattering to demonstrate checkerboard charge order in the FeO2 planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on “hidden order” in other materials

Atomic dynamics of the i-ScZnMg and its 1/1 approximant phase: experiment and simulation

International audienceQuasicrystals are long range ordered materials which lack translational invariance so that the study of their physical properties remains a challenging problem. In order to study the respective influence of the local order and of the long range order (periodic or quasiperiodic) on lattice dynamics, we have carried out inelastic x-ray and neutron scattering experiments on single grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant. Besides the overall similarities and the existence of a pseudo gap in the transverse dispersion relation, marked differences are observed, the pseudo gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of pseudo Brillouin zone in the quasicrystal. These results are compared to simulations on atomic models and using oscillating pair potentials which have been fitted against ab-initio data. The simulated response function reproduces both the dispersion relation but also the observed intensity distribution in the measured spectra. The partial vibrational density of states, projected on the cluster shells, is computed from this model

Phonons et Phasons dans les quasicristaux de symetrie icosaedrique et dans leurs approximants 1/1 periodiques

The static and dynamical responses associated with phonons and phasons are comparedin icosahedral quasicrystals and their cubic 1/1 approximants. Quasicristals and approximants sharea same local order within large atomic clusters of icosahedral shape (diameter ~ 1.6 nm). However,the long range order is quasiperiodic in the quasicrystal whereas it is periodic in the approximant.Quasiperiodicity yields new hydrodynamic modes called phasons. Phonons exist in the quasicrystaland in the approximant.We measured the distribution of the diffuse intensity near Bragg peaks in the Zn-Scapproximant phase and in the i-Zn-X-Sc quasicristalline phases with X = Mg, Ag, Co. In the Zn-Scapproximant, the thermal diffuse scattering due to phonons is observed. In the Zn-X-Sc phases,there is an additional diffuse intensity signal which one is due to phasons. The extracted phasonelastic contants are shown to vary with the chemical nature of the element X.We studied the dynamics of long-wavelength phasons using coherent X-rays in the i-Al-Pd-Mn phase. Phasons are activated above 600°C. The dynamics is diffusive. At 650°C, for phasonshaving a wavelength of 90 nm, the typical relaxation time is of the order of 100 s.We investigated the phonon dynamics in the i-Zn-Mg-Sc and 1/1 Zn-Sc phases, and in thei-Cd-Yb and 1/1 Cd-Yb phases using neutron and X-ray inelastic scattering. The dynamicalstructure factor S(Q, E) are similar in the quasicrystal and its approximant which shows theimportance of the local order on the dynamical response of vibrational modes in those structures.Some differences are nevertheless observed.Les réponses statiques et dynamiques associées aux phonons et aux phasons sontcomparées dans des quasicristaux de symétrie icosaédrique et dans leurs approximants 1/1cubiques. Quasicristaux et approximants partagent un même ordre local caractérisé par des amasatomiques icosaédriques de grande taille (diamètre ~ 1.6 nm). L'ordre à longue portée estquasipériodique dans le quasicristal alors que périodique dans l'approximant. Les phasons sont denouveaux modes hydrodynamiques induits par la quasipériodicité. Les phonons existent dans lequasicristal et dans l'approximant.Nous avons mesuré la distribution de l'intensité diffuse autour des pics de Bragg dans laphase approximante Zn-Sc et dans les phases quasicristallines i-Zn-X-Sc (X = Mg, Ag, Co). Dansla phase Zn-Sc, la diffusion diffuse thermique due aux phonons est seule observée. Dans les phasesi-Zn-X-Sc, il y a un signal diffus supplémentaire dû aux phasons. Les constantes élastiques dephason déterminées varient avec la nature de l'élément X.La dynamique des phasons est étudiée en diffusion cohérente des rayons X dans la phase i-Al-Pd-Mn. Les phasons sont activés au-dessus de 600°C. La dynamique est diffusive avec, à650°C, des temps de relaxation de 100 s une longueur d'onde des modes de 90 nm.La dynamique des phonons est mesurée dans les phases i-Zn-Mg-Sc et 1/1-Zn-Sc puis dansles phases i-Cd-Yb et 1/1-Cd-Yb en diffusions inélastiques des neutrons et des rayons X. Lesfacteurs de structure dynamiques sont similaires dans le quasicristal et son approximant ce quirévèle l'importance de l'ordre local sur la réponse dynamique des modes de vibration dans cesstructures. Des différences sont néanmoins observées

Phonons et phasons dans les quasicristaux de symétrie icosaédrique et dans leurs approximants 1/1 périodiques

Les réponses statiques et dynamiques associées aux phonons et aux phasons sont comparées dans des quasicristaux de symétrie icosaédrique et dans leurs approximants 1/1 cubiques. Quasicristaux et approximants partagent un même ordre local caractérisé par des amas atomiques icosaédriques de grande taille (environ1.6 nm). L'ordre à longue portée est quasipériodique dans le quasicristal alors que périodique dans l'approximant. Les phasons sont de nouveaux modes hydrodynamiques induits par la quasipériodicité. Les phonons existent dans le quasicristal et dans l'approximant. Nous avons mesuré la distribution de l'intensité diffuse autour des pics de Bragg dans la phase approximante Zn-Sc et dans les phases quasi cristallines i-Zn-X-Sc (X = Mg, Ag, Co). Dans la phase Zn-Sc, la diffusion diffuse thermique due aux phonons est seule observée. Dans les phases i-Zn-X-Sc, il y un signal diffus supplémentaire dû aux phasons. Les constantes élastiques de phason déterminées varient avec la nature de l'élément X. La dynamique des phasons est étudiée en diffusion cohérente des rayons X dans la phase i-AI-Pd-Mn. Les phasons sont activés au-dessus de 600C. La dynamique est diffusive avec, à 650C, des temps de relaxation de environ 100 s pour une longueur d'onde des modes de environ 90 nm.La dynamique des phonons est mesurée dans les phases i-Zn-Mg-Sc et III-Zn-Sc puis dans les phases i-Cd- Yb et 1/1-Cd- Yb en diffusions inélastiques des neutrons et des rayons X. Les facteurs de structure dynamiques sont similaires dans le quasicristal et son approximant ce qui révèle l'importance de l'ordre local sur la réponse dynamique des modes de vibration dans ces structures. Des différences sont néanmoins observéeGRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF