Role of Magnetic Defects in Tuning Ground States of Magnetic Topological Insulators.

Magnetic defects play an important, but poorly understood, role in magnetic topological insulators (TIs). For example, topological surface transport and bulk magnetic properties are controlled by magnetic defects in Bi Se -based dilute ferromagnetic (FM) TIs and MnBi Te (MBT)-based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, the inelastic neutron scattering data show that a fraction of the Mn defects in Sb Te form strong AFM dimer singlets within a quintuple block.

Magnetic properties and signatures of ordering in triangular lattice antiferromagnet KCeO.

The magnetic ground state and the crystalline electric field level scheme of the triangular lattice antiferromagnet are investigated. Below mK, develops signatures of magnetic order in specific heat measurements and low energy inelastic neutron scattering data. Trivalent ions in the local environment of this compound exhibit large splittings among the lowest three Kramers doublets defining for the free ion the sextet and a ground state doublet with dipole character, consistent with recent theoretical predictions in M.

Freezing of a Disorder Induced Spin Liquid with Strong Quantum Fluctuations.

Sr_{2}CuTe_{0.5}W_{0.5}O_{6} is a square-lattice magnet with superexchange between S=1/2Cu^{2+} spins mediated by randomly distributed Te and W ions.

3D scanning and 3D printing AlSi10Mg single crystal mounts for neutron scattering.

We present methods to quantify sample shapes and generate sample mounts as motivated by the needs of neutron scattering experiments. The 3D sample scanning was performed using photogrammetry and laser scanning, and a comparison is made between the two techniques. The aluminum alloy AlSi10Mg is shown to have favorable properties for many types of mounts used in neutron scattering.

Three-dimensional magnetism and the Dzyaloshinskii-Moriya interaction in = 3/2 kagome staircase CoVO.

Time-of-flight neutron data reveal spin waves in the ferromagnetic ground state of the kagome staircase material CoVO. While previous work has treated this material as quasi-two-dimensional, we find that an inherently three-dimensional description is needed to describe the spin wave spectrum throughout reciprocal space. Moreover, spin wave branches show gaps that point to an unexpectedly large Dzyaloshinskii-Moriya interaction on the nearest-neighbor bond, with ≥ /2.

Crystal structures and rotational dynamics of a two-dimensional metal halide perovskite (OA)PbI.

The extended charge carrier lifetime in metal halide perovskites is responsible for their excellent optoelectronic properties. Recent studies indicate that the superb device performance in these materials is intimately related to the organic cation dynamics. Here, we focus on the investigation of the two-dimensional hybrid perovskite, (CHNH)PbI (henceforth, OA = CHNH ).

Coexistence of Ferromagnetic and Stripe Antiferromagnetic Spin Fluctuations in SrCo_{2}As_{2}.

We use inelastic neutron scattering to study energy and wave vector dependence of spin fluctuations in SrCo_{2}As_{2}, derived from SrFe_{2-x}Co_{x}As_{2} iron pnictide superconductors. Our data reveal the coexistence of antiferromagnetic (AF) and ferromagnetic (FM) spin fluctuations at wave vectors Q_{AF}=(1,0) and Q_{FM}=(0,0)/(2,0), respectively. By comparing neutron scattering results with those of dynamic mean field theory calculation and angle-resolved photoemission spectroscopy experiments, we conclude that both AF and FM spin fluctuations in SrCo_{2}As_{2} are closely associated with a flatband of the e_{g} orbitals near the Fermi level, different from the t_{2g} orbitals in superconducting SrFe_{2-x}Co_{x}As_{2}.

Pulsed laser deposition films from a BaFeMoO target onto SrTiO[001]: Chemical and magnetic inhomogeneity.

Pulsed laser deposition films from BaFeMoO (BFMO) targets onto SrTiO[001] (STO) substrates have been reported previously to have non-zero magnetism at 300 K, a majority of magnetic ordering at 240 K that is less than the 370 K ordering temperature of polycrystalline BFMO, and suppressed saturation magnetization compared to polycrystalline BFMO. To interrogate these previously reported observations of BFMO on STO, we have used a combination of x-ray diffraction, atomic force microscopy, x-ray and neutron reflectivity, and x-ray photoelectron spectroscopy that shows inhomogeneities. The present results show off-stoichiometry on the A-site by incorporation of Sr from the substrate and on the B-site to have %Fe/%Mo > 1 by evolution of BaMoO.

Chloride-bridged, defect-dicubane {Ln4} core clusters: syntheses, crystal structures and magnetic properties.

Three chloride-bridged lanthanide compounds, [Ln4Cl6(CH3OH)12(OH)2]·4Cl·2CH3OH [Ln = Gd (), Dy () and Er ()], have been unexpectedly isolated by the reactions of LnCl3·6H2O and N,N'-bis(salicylidene)-1,2-(phenylene-diamine) (H2L). X-ray crystallographic analysis reveals a triclinic cell with a unique defect-dicubane {Ln4} core and the structure across this series is nominally isomorphic. Measurements of direct current magnetic susceptibility and isothermal magnetization give insight into the relevant cluster Hamiltonians for , , and , and alternating current susceptibility shows slow relaxation in , but not in or down to 2 K and up to 1 kHz.

Synthesis and size control of iron(II) hexacyanochromate(III) nanoparticles and the effect of particle size on linkage isomerism.

The controlled synthesis of monodisperse nanoparticles of the cubic Prussian blue analogue iron(II) hexacyanochromate(III) is reported along with a kinetic study, using cyanide stretching frequencies, showing the variations of the activation energy (E(a)) of the linkage isomerism as a function of the particle size. Highly reproducible, cubic-shaped iron(II) hexacyanochromate(III) nanocrystals, with sizes ranging from 2 to 50 nm, are synthesized using a microemulsion technique, whereas a bulk synthesis yields nonuniform less monodisperse particles with sizes greater than 100 nm. Monitoring the cyanide stretching frequency with FTIR spectroscopy shows that the rate of isomerization is faster for smaller particles.

Photomagnetic K(0.25)Ni(1-x)Co(x)[Fe(CN)6]·nH2O and K(0.25)Co[Fe(CN)6](0.75y)[Cr(CN)6](0.75(1-y))·nH2O Prussian blue analogue solid solutions.

Magnetically bistable solid solutions of Prussian blue analogues with chemical formulas of K(α)Ni(1-x)Co(x)[Fe(CN)(6)](β)·nH(2)O (Ni(1-x)Co(x)Fe) and K(α)Co(γ)[Fe(CN)(6)](y)[Cr(CN)(6)](1-y)·nH(2)O (CoFe(y)Cr(1-y)) have been synthesized and studied using mass spectrometry, Mössbauer spectroscopy, X-ray diffraction, temperature-dependent infrared spectroscopy, and dc magnetometry. These compounds provide insight into interfaces between the photomagnetic Co-Fe Prussian blue analogue and the high-T(C) Ni-Cr Prussian blue analogue that exist in high-T(C) photomagnetic heterostructures. This investigation shows that the bistability of Co-Fe is strongly modified by metal substitution, with Ni(1-x)Co(x)Fe stabilizing high-spin cobalt-iron pairs and CoFe(y)Cr(1-y) stabilizing low-spin cobalt-iron pairs, while both types of substitution cause a dramatic decrease in the bistability of the material.

Photoinduced magnetism in core/shell Prussian blue analogue heterostructures of K(j)Ni(k)[Cr(CN)6]l·nH2O with Rb(a)Co(b)[Fe(CN)6]c·mH2O.

Core/shell and core/shell/shell particles comprised of the Prussian blue analogues K(j)Ni(k)[Cr(CN)(6)](l)·nH(2)O (A) and Rb(a)Co(b)[Fe(CN)(6)](c)·mH(2)O (B) have been prepared for the purpose of studying persistent photoinduced magnetization in the heterostructures. Synthetic procedures have been refined to allow controlled growth of relatively thick (50-100 nm) consecutive layers of the Prussian blue analogues while minimizing the mixing of materials at the interfaces. Through changes in the order in which the two components are added, particles with AB, ABA, BA, and BAB sequences have been prepared.

Metal monophosphonates M{(2-C5H4NO)CH2PO3}(H2O)2 (M = Co, Ni, Mn, Cd): synthesis, structure, and magnetism.

Four isostructural metal monophosphonates, M{(2-C(5)H(4)NO)CH(2)PO(3)}(H(2)O)(2) with M = Co (1), Ni (2), Mn (3), and Cd (4), were synthesized and structurally characterized. These compounds show a double-chain structure in which the M(2)(μ-O)(2) dimers are connected by O-P-O bridges. The magnetic responses of 1-3 were investigated over a wide range of magnetic fields (up to 10 T) and temperatures (down to 50 mK).

Persistent photoinduced magnetism in heterostructures of prussian blue analogues.

Heterostructured ABA thin films consisting of two different Prussian blue analogues, where A is a ferromagnet and B is a photoinducible ferrimagnet, have been fabricated for the first time. This novel arrangement allows the magnetization to be decreased by irradiation with white light and significantly increases the ordering temperature of the photoinduced magnetism from 18 to 75 K.

Tuning the sign of photoinduced changes in magnetization: spin transitions in the ternary metal Prussian blue analogue Na(alpha)Ni(1-x)Co(x)[Fe(CN)6](beta) x nH2O.

Tuning the composition of the ternary transition-metal Prussian blue analogue Na(alpha)Ni(1-x)Co(x)[Fe(CN)(6)](beta) x nH(2)O allows the sign of the photoinduced change in magnetization to be controlled. The parent cobalt hexacyanoferrate material is well-known to display photoinduced and thermal charge-transfer-induced spin transitions (CTISTs). Upon partial replacement of Co ion sites with Ni(II), irradiation with halogen light can cause either an increase or a decrease in magnetization, depending upon the extent of Ni(II) substitution, the applied field, and the temperature.

Superparamagnetic Fe3O4SiO2 nanocomposites: enabling the tuning of both the iron oxide load and the size of the nanoparticles.

Using a water-in-oil microemulsion system, silica nanoparticles containing superparamagnetic iron oxide (SPIO) crystals have been prepared and characterized. With this method, the loading of iron oxide crystals, the thickness of the silica shells, and the overall particle sizes are tunable. Moving from low to high water concentration, within the microemulsion region, resulted in a gradual shift from larger particles, ca.