Physics

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Detailed 27Al and 63Cu nuclear magnetic resonance (NMR) experiments have been performed in between 4.5 and 295 K on a polycrystalline sample of CeCu3Al2 which has a Kondo temperature ∼11K. The NMR spectral features and Knight shift measurements show that in this compound, Cu occupy both c and g lattice sites, while Al occupy only the g sites. From the temperature dependence of Knight shift (K), the hyperfine fields for 63Cu and 27Al at the g sites have been estimated as 2.02(5) and 1.67(5)kOe/$\mu$B, respectively and that for 63Cu at c sites as -3.83(5)kOe/$\mu$B. Nuclear spin-lattice relaxation time (T1) measurements indicate that though the relaxation process is governed by fluctuations of magnetic interaction, nuclear quadrupolar interaction also has a significant contribution, especially towards relaxation of 63Cu in both c and g sites. For 27Al, K and T 1 have yielded the effective 4f-spin correlation rate 1/$\tau$4f. The behavior of its temperature dependence indicates that at low temperatures in CeCu3Al2, the valence state of cerium might not be stable. {\textcopyright} 2010 Elsevier B.V. All rights reserved.

World University root node

(SoNS) School of Natural Sciences

Physica B: Condensed Matter

27Al and 63Cu NMR studies on intermetallic Kondo compound CeCu3Al2

The effect of interfacial hydrogen bonding on the behavior of the freezing/melting processes in two organic liquids, namely, ethylene glycol [(CH2OH)2] and isopropanol [CH3CH(OH)CH 3], confined in nanopores of ZSM-5 zeolite has been investigated using the positron annihilation spectroscopy (PAS) and nuclear magnetic resonance (NMR) techniques. Both liquids have intermolecular hydrogen bonding and feel attractive interaction toward the surface of the confining wall, resulting in an increase in the freezing/melting temperature while confined in nanopores. This observation differs from our earlier report on the behavior of benzene confined in ZSM-5 as well as in silica pores wherein a depression in freezing temperature was seen due to a weakly attractive/repulsive interaction between benzene and the pore surface. The measured S parameter, o-Ps lifetime and intensity profiles across the freezing point of ethylene glycol confined in ZSM-5 are seen to be different from those of isopropanol, signifying the difference in the behavior of phase transition in these two liquids under confinement. It is to be noted that, unlike isopropanol, ethylene glycol has strong intramolecular hydrogen bonding. This causes the difference in the fluid-wall interfacial interaction between ethylene glycol and isopropanol within the confinement. The phase-transition behavior of these two confined liquids was also investigated using the NMR technique by studying the spin-spin relaxation time (T2). The T2 process in ethylene glycol is expressed as a sum of at least two distinct components exhibiting Gaussian decay, whereas in isopropanol, T2 is expressed as a sum of three components showing Lorentzian decay. The transitions from one component to another were seen to be consistent with the positron annihilation spectroscopic observation. {\textcopyright} 2010 American Chemical Society.

Journal of Physical Chemistry C

Effect of interfacial hydrogen bonding on the freezing/melting behavior of nanoconfined liquids

L 139 a NMR study was performed in grain-aligned (c→|| H→0) sample of LaCoPO and polycrystalline LaFePO. Knight shift is isotropic and temperature independent in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The spin-lattice relaxation rate in LaCoPO clearly reveals the existence of three-dimensional spin fluctuations both in the paramagnetic and ferromagnetic state over and above the dominant two-dimensional spin fluctuations in the paramagnetic state, observed earlier from P 31 NMR measurements in the same oriented sample. The spin fluctuation parameters in LaCoPO determined from L 139 a NMR relaxation and magnetization data, using the self-consistent renormalization theory, are in close agreement and follow the universal Rhodes-Wohlfarth curve. {\textcopyright} 2010 The American Physical Society.

Fulltext

Physical Review B - Condensed Matter and Materials Physics

Electron spin dynamics in grain-aligned LaCoPO: An itinerant ferromagnet

Systematic evolution of the 400 nm electroluminescence (EL) with increasing flash lamp annealing (FLA) temperature from 800 to 1100 °C in an Er-doped Ge-rich metal-oxide semiconductor structure is presented. No significant change in the 1535 nm Er EL is observed with increasing FLA temperature. Enhancement of the 400 nm EL decay time with rising FLA temperature is found to be associated with recrystallization of the damaged Ge clusters in the absence of Ge outdiffusion. The 400 nm EL quenching with continuous charge injection process is also discussed within the device operation time. © 2010 American Institute of Physics.

Journal of Applied Physics

Controlling blue-violet electroluminescence of Ge-rich Er-doped SiO 2 layers by millisecond annealing using flash lamps

APS March Meeting Abstracts

High Momentum Transfer Shallow Core-to-valence Spectroscopy in the Actinides

InAs quantum dots (QDs) were successfully formed in single-crystalline Si by sequential ion implantation and subsequent milliseconds range flash lamp annealing (FLA). Samples were characterized by μ-Raman spectroscopy, Rutherford Backscattering Spectrometry (RBS) high-resolution transmission electron microscopy (HRTEM) and low temperature photoluminescence (PL). The Raman spectrum shows two peaks at 215 and 235 cm-1 corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs phonon modes, respectively. The PL band at around 1.3 μm originates from the InAs QDs with an average diameter 7.5 ± 0.5 nm and corresponds to the increased band gap energy due to the strong quantum confinement size effect. The FLA of 20 ms is sufficient for InAs QDs formation. It also prevents the out-diffusion of implanted elements. Moreover, the silicon layer amorphized during ion implantation is recrystallized by solid-phase epitaxial regrowth during FLA. © Springer-Verlag 2010.

Applied Physics B: Lasers and Optics

Formation of InAs quantum dots in silicon by sequential ion implantation and flash lamp annealing

Magnetic atoms at surfaces are a rich model system for solid-state magnetic bits exhibiting either classical or quantum behaviour. Individual atoms, however, are difficult to arrange in regular patterns. Moreover, their magnetic properties are dominated by interaction with the substrate, which, as in the case of Kondo systems, often leads to a decrease or quench of their local magnetic moment. Here, we show that the supramolecular assembly of Fe and 1,4-benzenedicarboxylic acid molecules on a Cu surface results in ordered arrays of high-spin mononuclear Fe centres on a 1.5 nm square grid. Lateral coordination with the molecular ligands yields unsaturated yet stable coordination bonds, which enable chemical modification of the electronic and magnetic properties of the Fe atoms independently from the substrate. The easy magnetization direction of the Fe centres can be switched by oxygen adsorption, thus opening a way to control the magnetic anisotropy in supramolecular layers akin to that used in metallic thin films.

Nature Materials

Supramolecular control of the magnetic anisotropy in two-dimensional high-spin Fe arrays at a metal interface

We report (11)B and (195)Pt NMR Knight shift K and spin-lattice relaxation rate 1/T(1) in CePt(2)B(2)C in the range 4-315 K. The quadrupolar coupling constant, nu(Q) for boron nuclei is 790 +/- 10 kHz. The change of hyperfine field, H(hf), is observed below 30 K in the K versus susceptibility, chi, plot. The calculated value of H(hf) at the (11)B ((195)Pt) is 0.156 (6.86) kOe/mu(B) in the range 30-300 K and approximately 0 (0.22) kOe/mu(B) below 30 K. The 1/T(1) versus T curve shows some exotic behavior. The Ce 4f spin contribution to the nuclear relaxation rate (1/T(1f)) in each case is obtained by subtracting the T(1K)(-1) estimated from its La analog, i.e. LaPt(2)B(2)C. In the case of (11)B resonance, in the temperature range of 300-100 K, (1/T(1f)) is independent of T, suggesting a Curie-Weiss behavior of the imaginary part of the dynamic susceptibility. It then shows a slow but continuous increment in the range 100-70 K, indicating a signature of the development of short-range magnetic correlation among the Ce 4f spins. Below 70 K, this enhancement of 1/T(1f) is completely suppressed and it decreases sharply, indicating a suppression of the effect of magnetic correlation, due to the dominance of the Kondo effect over the RKKY interaction. 1/T(1f), follows approximately T(alpha), with an exponent alpha approximately 0.7 in the range 4-30 K for (195)Pt and in the range 8-30 K for (11)B resonance. This is a characteristics of a non-Fermi-liquid like behavior. However, in the case of (11)B, there is again a clear change in the slope of the 1/T(1f) versus T curve below 8 K, with the value of alpha = 1.0, as if the behavior of the conduction electrons approaches towards a Fermi liquid, when probed near the (11)B site.

Journal of Physics: Condensed Matter

11 B and 195 Pt NMR study of heavy-fermion compound CePt 2 B 2 C

The anomalous wear-out phenomena of Eu-implanted metal-oxide-semiconductor devices were investigated. It will be shown that in contrast to other rare earth elements the electroluminescence (EL) intensity of Eu-implanted SiO2 layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances, this rise may amount up to two orders of magnitude. The EL behavior will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy and Rutherford backscattering spectroscopy were applied to trace the development of Eu/Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer. The hydrogen profile within the SiO2-SiON interface region was determined by nuclear reaction analysis. Current-voltage characteristics, EL decay times, and the progression of the voltage and the EL spectrum with increasing charge injection were measured to study charge and trapping phenomena in the oxide layer to reveal details of the EL excitation mechanism. A first qualitative model for the anomalous life time behavior is proposed. © 2009 American Institute of Physics.

Anomalous wear-out phenomena of europium-implanted light emitters based on a metal-oxide-semiconductor structure

We demonstrate that the recent paper by Jana and Roy entitled "Non-Hermitian quantum mechanics with minimal length uncertainty" [SIGMA 5 (2009), 083, 7 pages, arXiv:0908.1755] contains various misconceptions. We compare with an analysis on the same topic carried out previously in our manuscript [arXiv:0907.5354]. In particular, we show that the metric operators computed for the deformed non-Hermitian Swanson models differs in both cases and is inconsistent in the former.