100 research outputs found
Measuring Motional Dynamics of (CH) NH in the Perovskite-Like Metal--Organic Framework [(CH) NH][Zn(HCOO)]: The Value of Low-Frequency Electron Paramagnetic Resonance
Dimethylammonium zinc formate (DMAZnF) is the precursor for a large family of
multiferroics, materials which display co-existing magnetic and dielectric
ordering. However, the mechanism underlying these orderings remains unclear.
While it is generally believed that the dielectric transition is related to the
freezing of the order-disorder dynamics of the dimethylammonium (DMA+) cation,
no quantitative data on this motion are available. We surmise that this is due
to the fact that the timescale of this cationic motion is on the borderline of
the timescales of experimental techniques used in earlier reports. Using
multifrequency EPR, we find that the timescale of this motion is ~ 5 x 10 -9 s.
Thus, S-band (4 GHz) EPR spectroscopy is presented as the technique of choice
for studying these motional dynamics. This work highlights the value of the
lower-frequency end of EPR spectroscopy. The data are interpreted using DFT
calculations and provide direct evidence for the motional freezing model of the
ferroelectric transition in these metal-organic frameworks with the ABX3
perovskite-like architecture
Study of the local field distribution on a single-molecule magnet-by a single paramagnetic crystal; a DPPH crystal on the surface of an Mn12-acetate crystal
The local magnetic field distribution on the subsurface of a single-molecule
magnet crystal, SMM, above blocking temperature (T >> Tb) detected for a very
short time interval (~ 10-10 s), has been investigated. Electron Paramagnetic
Resonance (EPR) spectroscopy using a local paramagnetic probe was employed as a
simple alternative detection method. An SMM crystal of
[Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-acetate) and a crystal of 2,2-
diphenyl-1-picrylhydrazyl (DPPH) as the paramagnetic probe were chosen for this
study. The EPR spectra of DPPH deposited on Mn12-acetate show additional
broadening and shifting in the magnetic field in comparison to the spectra of
the DPPH in the absence of the SMM crystal. The additional broadening of the
DPPH linewidth was considered in terms of the two dominant electron spin
interactions (dipolar and exchange) and the local magnetic field distribution
on the crystal surface. The temperature dependence of the linewidth of the
Gaussian distribution of local fields at the SMM surface was extrapolated for
the low temperature interval (70-5 K)
Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedron system
We report on the magnetic excitation spectrum of the coupled spin tetrahedral
system CuTeOCl using Raman scattering on single
crystals. The transition to an ordered state at T=18.2 K evidenced
from thermodynamic data leads to the evolution of distinct low-energy magnetic
excitations superimposed by a broad maximum. These modes are ascribed to
magnons with different degree of localization and a two-magnon continuum. Two
of the modes develop a substantial energy shift with decreasing temperature
similar to the order parameter of other Neel ordered systems. The other two
modes show only a negligible temperature dependence and dissolve above the
ordering temperature in a continuum of excitations at finite energies. These
observations point to a delicate interplay of magnetic inter- and
intra-tetrahedra degrees of freedom and an importance of singlet fluctuations
in describing a spin dynamics.Comment: 7pages, 6figures, 1tabl
Incommensurate Transverse Anisotropy Induced by Disorder and Spin-Orbit-Vibron Coupling in Mn12-acetate
It has been shown within density-functional theory that in Mn-acetate
there are effects due to disorder by solvent molecules and a coupling between
vibrational and electronic degrees of freedom. We calculate the in-plane
principal axes of the second-order anisotropy caused by the second effect and
compare them with those of the fourth-order anisotropy due to the first effect.
We find that the two types of the principal axes are not commensurate with each
other, which results in a complete quenching of the tunnel-splitting
oscillation as a function of an applied transverse field.Comment: Will be presented at MMM conference 200
Structural and Optical Properties of Nanocrystalline TiO2 with Multiwalled Carbon Nanotubes and Its Photovoltaic Studies Using Ru(II) Sensitizers
In this study, the in situ sol–gel method has been deployed to prepare the titanium dioxide/multiwalled carbon nanotubes (TiO2/MWCNTs) nanocomposite (NCs) powders with varying content of MWCNTs (0.01–1.0 wt %), to construct the dye-sensitized solar cells (DSSCs). First, binder-free NCs were deposited on a transparent-conducting F:SnO2 (FTO) glass substrate by a doctor-blade technique and then anchored with Ru(II)-based dyes to either N719 or ruthenium phthalocyanine (RuPc). The structural and optical properties and interconnectivity of the materials within the composite are investigated thoroughly by various spectral techniques (XRD, XPS, Raman, FT-IR, and UV–vis), electron microscopy (HRTEM), and BET analysis. The experimental results suggest that the ratio of MWCNTs and TiO2 in NCs, morphology, and their interconnectivity influenced their structural, optical, and photovoltaic properties significantly. Finally, the photovoltaic performances of the assembled DSSCs with different content of MWCNTs to TiO2 films anchored with two different dyes were tested under one sun irradiation (100 mW/cm2). The measured current–voltage (IV) curve and incident photon-to-current conversion efficiency (IPCE) spectra of TiO2/0.1 wt % MWCNTs ([email protected] C) for N719 dye show three times more power conversion efficiency (η = 6.21%) which is opposed to an efficiency (η = 2.07%) of [email protected] C for RuPc dye under the same operating conditions
Molecular spin qubits based on lanthanide ions encapsulated in cubic polyoxopalladates: design criteria to enhance quantum coherence
The family of cubic polyoxopalladates encapsulating lanthanide ions [LnPd12(AsPh)8O32]5− where Ln = Tb, Dy, Ho, Er and Tm, is magnetically characterised and theoretically described by the Radial Effective Charge (REC) model and a phenomenological crystal-field approach using the full-hamiltonian, in the SIMPRE and CONDON packages respectively. The lack of anisotropy generates an extraordinarily rich energy level structure at low temperatures, which allows us to study how such a structure is affected by lifting the strict cubic symmetry and/or by applying an external magnetic field. In particular, we will explore the possibility of using these cubic Ln complexes as spin-qubits. We will focus on the Ho derivative. We find that it is possible to reach a regime where decoherence caused by the nuclear spin bath is quenched for moderate axial compression of the cube and small magnetic fields.FP7-ERC-247384ERC-2014-CoG/ 647301MAT2014-56143-RCTQ2014-52758-PThe family of cubic polyoxopalladates encapsulating lanthanide ions [LnPd12(AsPh)8O32]5− where Ln = Tb, Dy, Ho, Er and Tm, is magnetically characterised and theoretically described by the Radial Effective Charge (REC) model and a phenomenological crystal-field approach using the full-hamiltonian, in the SIMPRE and CONDON packages respectively. The lack of anisotropy generates an extraordinarily rich energy level structure at low temperatures, which allows us to study how such a structure is affected by lifting the strict cubic symmetry and/or by applying an external magnetic field. In particular, we will explore the possibility of using these cubic Ln complexes as spin-qubits. We will focus on the Ho derivative. We find that it is possible to reach a regime where decoherence caused by the nuclear spin bath is quenched for moderate axial compression of the cube and small magnetic fields
Burden of cancer in Malawi; common types, incidence and trends: National population-based cancer registry
Single Molecule Chemistry and Physics: An Introduction By Chen Wang and Chunli Bai (National Center for Nanoscience and Technology, Beijing, China). From the Series: Nanoscience and Technology. Edited by P. Avouris, B. Bhushan, D. Bimberg, K. von Klitzing, H. Sakaki, and R. Wiesendanger. Springer: Berlin, Heidelberg, New York. 2006. xii + 304 pp. $119.00. ISBN 3-540-25369-6.
Apert′s Syndrome: A Rare Case Report
Apert′s syndrome /Acrocephalosyndactyly is a rare, congenital disorder characterized by craniosynostosis, midfacial malformations and symmetrical syndactyly. It is caused by a genetic mutation in the FGFR2 gene on chromosome 10. Although the syndrome has typical clinical features, the relative rarity of the condition still poses a diagnostic dilemma. Considering the general paucity of cases in the Indian literature, we present a case report of a 14-year-old female having all the features of classical Apert′s syndrome
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