Probing spin waves in CoO nanoparticles for magnonics applications.

The magnetic properties of spinel nanoparticles can be controlled by synthesizing particles of a specific shape and size. The synthesized nanorods, nanodots and cubic nanoparticles have different crystal planes selectively exposed on the surface. The surface effects on the static magnetic properties are well documented, while their influence on spin waves dispersion is still being debated.

Correlations and incipient antiferromagnetic order within the linear Mn chains of metallic TiMnBi.

We report measurements on TiMnBi, where a crystal structure involving linear chains of Mn ions suggests one-dimensional magnetic character. The electrical resistivity is metallic, consistent with the results of electronic-structure calculations that find a robust Fermi surface albeit with moderate electronic correlations. A Curie-Weiss fit to the magnetic susceptibility suggests that the Mn moments are in the low-spin = 1/2 configuration.

Spinon confinement and a sharp longitudinal mode in YbPtPb in magnetic fields.

The fundamental excitations in an antiferromagnetic chain of spins-1/2 are spinons, de-confined fractional quasiparticles that when combined in pairs, form a triplet excitation continuum. In an Ising-like spin chain the continuum is gapped and the ground state is Néel ordered. Here, we report high resolution neutron scattering experiments, which reveal how a magnetic field closes this gap and drives the spin chains in YbPtPb to a critical, disordered Luttinger-liquid state.

Combined computational and experimental investigation of the LaCuO S (0 ≤ ≤ 4) quaternary system.

The lack of a mechanistic framework for chemical reactions forming inorganic extended solids presents a challenge to accelerated materials discovery. We demonstrate here a combined computational and experimental methodology to tackle this problem, in which in situ X-ray diffraction measurements monitor solid-state reactions and deduce reaction pathways, while theoretical computations rationalize reaction energetics. The method has been applied to the LaCuO S (0 ≤ ≤ 4) quaternary system, following an earlier prediction that enhanced superconductivity could be found in these new lanthanum copper(II) oxysulfide compounds.

Local quantum phase transition in YFeAl.

A phase transition occurs when correlated regions of a new phase grow to span the system and the fluctuations within the correlated regions become long lived. Here, we present neutron scattering measurements showing that this conventional picture must be replaced in YFeAl, a compound that forms naturally very close to a [Formula: see text] quantum phase transition. Fully quantum mechanical fluctuations of localized moments are found to diverge at low energies and temperatures; however, the fluctuating moments are entirely without spatial correlations.

Reduction of Raman scattering and fluorescence from anvils in high pressure Raman scattering.

We describe a new design and use of a high pressure anvil cell that significantly reduces the Raman scattering and fluorescence from the anvils in high pressure Raman scattering experiments. The approach is particularly useful in Raman scattering studies of opaque, weakly scattering samples. The effectiveness of the technique is illustrated with measurements of two-magnon Raman scattering in LaCuO.

Orbital-exchange and fractional quantum number excitations in an f-electron metal, Ybâ‚‚Ptâ‚‚Pb.

Exotic quantum states and fractionalized magnetic excitations, such as spinons in one-dimensional chains, are generally expected to occur in 3d transition metal systems with spin 1/2. Our neutron-scattering experiments on the 4f-electron metal Yb2Pt2Pb overturn this conventional wisdom. We observe broad magnetic continuum dispersing in only one direction, which indicates that the underlying elementary excitations are spinons carrying fractional spin-1/2.

An itinerant antiferromagnetic metal without magnetic constituents.

The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local moments. Surprisingly, there are very few known examples of materials that are close to the itinerant limit, and their properties are not universally understood. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn2 and Sc3In, the understanding of their magnetic ground states draws on the existence of 3d electrons subject to strong spin fluctuations.

Protected Fe valence in quasi-two-dimensional α-FeSi2.

We report the first comprehensive study of the high temperature form (α-phase) of iron disilicide. Measurements of the magnetic susceptibility, magnetization, heat capacity and resistivity were performed on well characterized single crystals. With a nominal iron d(6) configuration and a quasi-two-dimensional crystal structure that strongly resembles that of LiFeAs, α-FeSi2 is a potential candidate for unconventional superconductivity.

Quantum critical fluctuations in layered YFe2Al10.

The absence of thermal fluctuations at T = 0 makes it possible to observe the inherently quantum mechanical nature of systems where the competition among correlations leads to different types of collective ground states. Our high precision measurements of the magnetic susceptibility, specific heat, and electrical resistivity in the layered compound YFe2Al10 demonstrate robust field-temperature scaling, evidence that this system is naturally poised without tuning on the verge of ferromagnetic order that occurs exactly at T = 0, where magnetic fields drive the system away from this quantum critical point and restore normal metallic behavior.

Intrinsic nanostructure in Zr2-xFe4Si16-y(x = 0.81, y = 6.06).

We present a study of the crystal structure and physical properties of single crystals of a new Fe-based ternary compound, Zr2-xFe4Si16-y(x = 0.81, y = 6.06).

New Kagome metal Sc₃Mn₃Al₇Si₅ and its gallium-doped analogues: synthesis, crystal structure, and physical properties.

We report the synthesis, crystal structure, and basic properties of the new intermetallic compound Sc3Mn3Al7Si5. The structure of the compound was established by single-crystal X-ray diffraction, and it crystallizes with a hexagonal structure (Sc3Ni11Si4 type) with Mn atoms forming the Kagome nets. The dc magnetic susceptibility measurements reveal a Curie-Weiss moment of ~0.

Size-dependent vibronic coupling in α-Fe2O3.

We report the discovery of finite length scale effects on vibronic coupling in nanoscale α-Fe2O3 as measured by the behavior of vibronically activated d-d on-site excitations of Fe(3+) as a function of size and shape. An oscillator strength analysis reveals that the frequency of the coupled symmetry-breaking phonon changes with size, a crossover that we analyze in terms of increasing three-dimensional character to the displacement pattern. These findings demonstrate the flexibility of mixing processes in confined systems and suggest a strategy for both enhancing and controlling charge-lattice interactions in other materials.

Spin liquids and antiferromagnetic order in the Shastry-Sutherland-lattice compound Yb2Pt2Pb.

We present measurements of the magnetic susceptibility χ and the magnetization M of single crystals of metallic Yb(2)Pt(2)Pb, where localized Yb moments lie on the dimerized and frustrated Shastry-Sutherland lattice (SSL). Strong magnetic frustration is found in this quasi-two-dimensional system, which orders antiferromagnetically at T(N) = 2.02 K from a paramagnetic liquid of Yb dimers, having a gap Δ = 4.

From antiferromagnetic insulator to correlated metal in pressurized and doped LaMnPO.

Widespread adoption of superconducting technologies awaits the discovery of new materials with enhanced properties, especially higher superconducting transition temperatures T(c). The unexpected discovery of high T(c) superconductivity in cuprates suggests that the highest T(c)s occur when pressure or doping transform the localized and moment-bearing electrons in antiferromagnetic insulators into itinerant carriers in a metal, where magnetism is preserved in the form of strong correlations. The absence of this transition in Fe-based superconductors may limit their T(c)s, but even larger T(c)s may be possible in their isostructural Mn analogs, which are antiferromagnetic insulators like the cuprates.

Nanospheres of a new intermetallic FeSn5 phase: synthesis, magnetic properties and anode performance in Li-ion batteries.

We synthesized monodisperse nanospheres of an intermetallic FeSn(5) phase via a nanocrystal-conversion protocol using preformed Sn nanospheres as templates. This tetragonal phase in P4/mcc space group, along with the defect structure Fe(0.74)Sn(5) of our nanospheres, has been resolved by synchrotron X-ray diffraction and Rietveld refinement.

Heavy fermion compounds on the geometrically frustrated Shastry-Sutherland lattice.

We present measurements of the basic properties of Ce(2)Ge(2)Mg, Yb(2)Pt(2)Pb and Ce(2)Pt(2)Pb, which are members of a new class of geometrically frustrated magnets R(2)T(2)X (R = rare earth, T = transition metal, X = main group). Here, the moment-bearing R atoms are confined to layers where they are arranged in the Shastry-Sutherland lattice. Magnetic susceptibility and specific heat measurements indicate that Ce(2)Ge(2)Mg orders antiferromagnetically at 9.

Magnetic transition and spin fluctuations in the unconventional antiferromagnetic compound Yb₃Pt₄.

Muon spin rotation and relaxation measurements have been carried out on the unconventional antiferromagnet Yb3Pt4. Oscillations are observed below T(N) = 2.22(1) K, consistent with the antiferromagnetic (AFM) Néel temperature observed in bulk experiments.

Ionothermal synthesis and magnetic studies of novel two-dimensional metal-formate frameworks.

Five novel two-dimensional frameworks containing formate-bridged metal-centered octahedra are synthesized ionothermally from two ionic liquids previously unused as solvents in hybrid synthesis, 2-hydroxyethylammonium (HEA) formate, and 1-hydroxy-3-proplyammonium (HPA) formate. Templating effects of the cation from each ionic liquid drive the formation of different structures. [NH(3)C(2)H(4)OH](2)[M(CHO(2))(4)] (1: M = Co, 2: M = Ni) exhibit the same stoichiometry and connectivity as their manganese analogue (3: M = Mn), but the manganese form exhibits a different topology from 1 and 2.

Water-dispersible, multifunctional, magnetic, luminescent silica-encapsulated composite nanotubes.

A multifunctional one-dimensional nanostructure incorporating both CdSe quantum dots (QDs) and Fe(3)O(4) nanoparticles (NPs) within a SiO(2)-nanotube matrix is successfully synthesized based on the self-assembly of preformed functional NPs, allowing for control over the size and amount of NPs contained within the composite nanostructures. This specific nanostructure is distinctive because both the favorable photoluminescent and magnetic properties of QD and NP building blocks are incorporated and retained within the final silica-based composite, thus rendering it susceptible to both magnetic guidance and optical tracking. Moreover, the resulting hydrophilic nanocomposites are found to easily enter into the interiors of HeLa cells without damage, thereby highlighting their capability not only as fluorescent probes but also as possible drug-delivery vehicles of interest in nanobiotechnology.

Synthesis and characterization of V2O3 nanorods.

In this work, VO2 nanorods have been initially generated as reactive nanoscale precursors to their subsequent conversion to large quantities of highly crystalline V2O3 with no detectable impurities. Structural changes in VO2, associated with the metallic-to-insulating transition from the monoclinic form to the rutile form, have been investigated and confirmed using X-ray diffraction and synchrotron data, showing that the structural transition is reversible and occurs at around 63 degrees C. When this VO2 one-dimensional sample was subsequently heated to 800 degrees C in a reducing atmosphere, it was successfully transformed into V2O3 with effective retention of its nanorod morphology.

Manipulating the magnetic structure of Co core/CoO shell nanoparticles: implications for controlling the exchange bias.

We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Néel temperature TN of approximately 235 K the magnetization of the CoO shell is modulated by two wave vectors, q1=(1/2 1/2 1/2)2pi/a and q2=(100)2pi/a.

Critical phenomena and the quantum critical point of ferromagnetic Zr(1-x)NbxZn2.

We present a study of the magnetic properties of Zr(1-x)NbxZn2, using an Arrott plot analysis of the magnetization. The Curie temperature Tc is suppressed to zero temperature for Nb concentration xc = 0.083+/-0.

Extended versus local fluctuations in quantum critical Ce(Ru1-xFex)2Ge2 (x=xc=0.76).

We present inelastic neutron scattering experiments, performed near the antiferromagnetic quantum critical point in Ce(Ru0.24Fe0.76)2Ge2.

Magnetic correlations and the quantum critical point of UCu5-xPdx (x = 1,1.5).

We have used inelastic neutron scattering to determine the magnetic susceptibility chi(q,omega,T) of the non-Fermi-liquid compounds UCu(5-x)Pdx (x = 1,1.5) for energies omega between 0.2 and 2 meV, and for temperatures T between 1.