A5080302212- Magnetic properties of thin films
- Magnetic and transport properties of perovskites and related materials
- Multiferroics and related materials
- Advanced Condensed Matter Physics
- Magnetic Properties and Applications
- Physics of Superconductivity and Magnetism
- ZnO doping and properties
- Characterization and Applications of Magnetic Nanoparticles
- Magnetic Properties of Alloys
- Quantum and electron transport phenomena
- Magnetic Properties and Synthesis of Ferrites
- Electronic and Structural Properties of Oxides
- Iron oxide chemistry and applications
- Rare-earth and actinide compounds
- Geomagnetism and Paleomagnetism Studies
- Surface and Thin Film Phenomena
- Theoretical and Computational Physics
- Ferroelectric and Piezoelectric Materials
- Advanced X-ray Imaging Techniques
- Semiconductor materials and devices
- Heusler alloys: electronic and magnetic properties
- Metalloenzymes and iron-sulfur proteins
- Metal and Thin Film Mechanics
- GaN-based semiconductor devices and materials
- Magneto-Optical Properties and Applications
Argonne National Laboratory
2012-2022
Bryn Mawr College
2014
Colorado State University
2014
American Physical Society
2014
Temple University
2014
National Renewable Energy Laboratory
2012
University of Arizona
1999-2004
Johns Hopkins University
1991-1996
University of Baltimore
1995
The crystal and magnetic structures of single-crystalline hexagonal LuFeO(3) films have been studied using x-ray, electron, neutron diffraction methods. polar structure these are found to persist up 1050 K; the switchability behavior is observed at room temperature, indicating ferroelectricity. An antiferromagnetic order was shown occur below 440 K, followed by a spin reorientation resulting in weak ferromagnetic 130 K. This observation coexisting multiple ferroic orders demonstrates that...
We report direct imaging by means of x-ray photoemission electron microscopy the dynamics magnetic vortices confined in micron-sized circular permalloy dots that are 30 nm thick. The vortex core positions oscillate on a 10 ns time scale self-induced magnetostatic potential well after in-plane field is turned off. measured oscillation frequencies as function aspect ratio agreement with theoretical calculations presented for same geometry.
We investigate structural coupling of the MnO6 octahedra across a film/substrate interface and resultant changes physical properties ultrathin La2/3Sr1/3MnO3 (LSMO) films. In order to isolate effect interfacial octahedral behavior from that epitaxial strain, LSMO films are grown on substrates with different symmetry similar lattice parameters. Ultrathin show an increased magnetization electrical conductivity cubic (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) compared those orthorhombic NdGaO3 (NGO)...
We present the refinement of crystal structure charge-ordered ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$, based on single-crystal x-ray diffraction data. The arrangement different Fe-valence states, determined with bond-valence-sum analysis, corresponds to a stacking charged Fe bilayers, in contrast polar bilayers previously suggested. This is supported by an analysis magnetic circular dichroism spectra, which also evidences strong charge-spin coupling. nonpolar are inconsistent charge order...
As interest in magnetic devices has increased over the last 20 years, research into nanomagnetism experienced a corresponding growth. Device applications from storage to logic have compelled influence of geometry and finite size on magnetism excitations, particular where smallest dimensions reach important interaction length scales. The dynamical behavior nanoscale magnets is an especially subset research, as these phenomena are both critical for device physics profoundly influenced by size....
Inverted soft/hard, in contrast to conventional hard/soft, bi-magnetic core/shell nanoparticles of MnxFe3−xO4/FexMn3−xO4 with two different core sizes (7.5 and 11.5 nm) fixed shell thickness (∼0.6 have been synthesized. The structural characterization suggests that the particles an interface a graded composition. magnetic confirms inverted soft/hard structure evidences strong exchange coupling between shell. Moreover, larger soft exhibit smaller coercivities loop shifts, but blocking...
While the synthesis of ABO3 perovskite films has enabled new strategies to control functionality this material class, chemistries that have been realized in thin film form constitute only a fraction those accessible bulk chemists. Here, we report oxyfluoride films, where incorporation F may provide means tune physical properties by modifying electronic structure. Fluorination is achieved spin coating poly(vinylidene fluoride) (PVDF) solution onto oxygen-deficient films. The film/polymer...
The coexistence and coupling of ferroelasticity magnetic ordering in a single material offers great opportunity to realize novel devices with multiple tuning knobs. Complex oxides are particularly promising class materials find multiferroic interactions due their rich phase diagrams, sensitive external perturbations. Still, there very few examples these systems. Here, we report the observation twin domains ferroelastic LaCoO3 epitaxial films geometric control structural symmetry intimately...
The anomalous Hall effect (AHE) is an intriguing transport phenomenon occurring typically in ferromagnets as a consequence of broken time reversal symmetry and spin-orbit interaction. It can be caused by two microscopically distinct mechanisms, namely, skew or side-jump scattering due to chiral features the disorder scattering, intrinsic contribution directly linked topological properties Bloch states. Here we show that AHE artificially engineered materials which it originally absent...
Abstract Magnetic interlayer coupling is one of the central phenomena in spintronics. It has been predicted that sign can be manipulated by electric fields, instead currents, thereby offering a promising low energy magnetization switching mechanism. Here we present experimental demonstration voltage-controlled new perpendicular magnetic tunnel junction system with GdO x barrier, where large anisotropy and sizable tunnelling magnetoresistance have achieved at room temperature. Owing to...
The magnetic phases of fcc Fe(100) in $\mathrm{Fe}(100)/{\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Au}}_{x}(100)$ multilayers with lattice parameters the range $a\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.606$ to 3.704 \AA{} have been studied using M\"ossbauer spectroscopy and SQUID magnetometry. Fe layers a two-phase structure consisting low-spin antiferromagnetic (AF) high-spin ferromagnetic (FM) phase. average moment relative population FM both increase $a$, but hyperfine field...
The authors report a soft x-ray absorption spectroscopy and magnetic circular dichroism study of the ferromagnetism in pulsed-laser-deposited Cu-doped ZnO thin films, which display robust room-temperature ferromagnetic signatures using bulk magnetization probes. In this work, probe spin asymmetries Cu 3d, O 2p, Zn 3d states individually. They find paramagnetic component originating from no signal or Zn. dichroic consistent with any these states.
Hexagonal LuFeO$_3$ films have been studied using x-ray absorption and optical spectroscopy. The crystal splittings of Fe$^{3+}$ are extracted as $E_{e'}-E_{e"}$=0.7 eV $E_{a_1'}-E_{e'}$=0.9 a 2.0 band gap is determined assuming direct gap. First-principles calculations confirm the experiments that relative energies field splitting states do follow $E_{a_1'}>E_{e'}>E_{e"}$ with slightly underestimated values 1.35 eV.
Abstract Nitrogenase enzymes catalyze the reduction of atmospheric dinitrogen to ammonia utilizing a Mo‐7Fe‐9S‐C active site, so‐called FeMoco cluster. and an analogous small‐molecule (Et 4 N)[(Tp)MoFe 3 S Cl ] cubane have both been proposed contain unusual spin‐coupled Mo III sites with (Mo)=1/2 non‐Hund configuration at atom. Herein, we present Fe L ‐edge X‐ray magnetic circular dichroism (XMCD) spectroscopy 2,3 XMCD MoFe protein (containing 8Fe‐7S P‐cluster sites). As P‐clusters =0 total...
We report induced Ga and As moments in ferromagnetic Ga(1-x)MnxAs detected using x-ray magnetic circular dichroism at the Mn, Ga, L(3,2) edges. Across a broad composition range, we find signals which indicate an 4s moment coupled antiparallel to Mn 3d moment, smaller parallel moment. The follows that of both doping temperature dependence. These results are consistent with recent predictions GaAs host support model carrier-mediated ordering involving As-derived valence band states.
We demonstrate an element-specific measurement of magnetization precession in a metallic ferromagnetic alloy, separating $\mathrm{Ni}$ and $\mathrm{Fe}$ moment motion ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$. Pump-probe x-ray magnetic circular dichroism, synchronized with short field pulses, is used to measure free oscillations up $2.6\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ elemental specificity rotational resolution $<2\ifmmode^\circ\else\textdegree\fi{}$. Magnetic moments residing on sites...
Epitaxial films of ${\text{Mn}}^{2+}$-doped ZnO were deposited by pulsed laser deposition on $\ensuremath{\alpha}{\text{-Al}}_{2}{\text{O}}_{3}(0001)$ using targets created from nanoparticles. Using x-ray absorption spectroscopy and magnetic circular dichroism, Mn(II) was found to substitute for Zn(II) in the w\"urtzite lattice with only a paramagnetic dichroic component Mn no either O or Zn. The dichroism reveals that, while substitutional, ${\text{Mn}}^{2+}$ distribution is not stochastic....
Using combined theoretical and experimental approaches, we studied the structural electronic origin of magnetic structure in hexagonal ${\mathrm{LuFeO}}_{3}$. Besides showing strong exchange coupling that is consistent with high ordering temperature, previously observed spin reorientation transition explained by theoretically calculated phase diagram. The this responsible for appearance spontaneous magnetization, identified theory verified x-ray diffraction absorption experiments.
We have used scanning electron microscopy with polarization analysis and photoemission to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay exchange interactions in asymmetrically coordinated vertices short-range dipole among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist frustrated at room temperature. Numerical simulations include long-range between agree images as-grown P2T...
In materials where two or more ordering degrees of freedom are closely matched in their free energies, coupling between them, multiferroic behavior can occur. These phenomena produce a very rich phase behavior, as well emergent phases that offer useful properties and opportunities to reveal novel transitions. The ordered alloy FeRh undergoes an antiferromagnetic ferromagnetic transition at ~375 K, which illustrates the interplay structural magnetic order mediated by delicate energy balance...
The magnetic interaction between rare-earth and Fe ions in hexagonal ferrites (h-REFeO3), may amplify the weak ferromagnetic moment on Fe, making these materials more appealing as multiferroics. To elucidate strength well of ions, element specific characterization is needed. Using X-ray circular dichroism, we have studied ferrimagnetism h-YbFeO3 by measuring magnetization Yb separately. results directly show anti-alignment at low temperature, with an exchange field about 17 kOe. 1.6 \muB...
To tune the magnetic properties of hexagonal ferrites, a family magnetoelectric multiferroic materials, by atomic-scale structural engineering, we studied effect distortion on ordering temperature (${T}_{N}$) in these materials. Using symmetry analysis, show that unlike most antiferromagnetic rare-earth transition-metal perovskites, larger leads to higher ${T}_{N}$ ferrites and manganites, because ${K}_{3}$ induces three-dimensional ordering, which is forbidden undistorted structure...
Strain engineering of epitaxial heterostructures offers opportunities to control the orbital degree freedom by lifting degeneracy ${e}_{g}$ states. Here, we show that occupation in $\mathrm{LaCo}{\mathrm{O}}_{3}$ (LCO) films can be switched between two degenerate bands with strain. The polarization nearly \ensuremath{-}100% (or 100%) is controlled depleting...