Critical Lattice Parameter Research Articles

Concomitant singularities of Yb-valence and magnetism at a critical lattice parameter of icosahedral quasicrystals and approximants

Non-Fermi-liquid (NFL), a significant deviation from Fermi-liquid theory, usually emerges near an order-disorder phase transition at absolute zero. Recently, a diverging susceptibility toward zero temperature was observed in a quasicrystal (QC). Since an electronic long-range ordering is normally absent in QCs, this anomalous behaviour should be a new type of NFL. Here we study high-resolution partial-fluorescence-yield x-ray absorption spectroscopy on Yb-based intermediate-valence icosahedral QCs and cubic approximant crystals (ACs), some of which are new materials, to unveil the mechanism of the NFL. We find that for both forms of QCs and ACs, there is a critical lattice parameter where Yb-valence and magnetism concomitantly exhibit singularities, suggesting a critical-valence-fluctuation-induced NFL. The present result provides an intriguing structure–property relationship of matter; size of a Tsai-type cluster (that is a common local structure to both forms) tunes the NFL whereas translational symmetry (that is present in ACs but absent in QCs) determines the nature of the NFL against the external/chemical pressure.

Manipulating Spin Alignments of (Y,Lu)1.7Fe17 Intermetallic Compounds via Unusual Thermal Pressure.

External pressure has been successfully employed to achieve desirable spin alignments in the field of materials science but is seriously restricted by the difficulty of reaching high pressure with conventional methods. The search for simple and effective ways to apply pressure on the lattice is challenging but intriguing. Here we report a new strategy to manipulate the spin alignments of (Y,Lu)1.7Fe17 intermetallic compounds through unusual thermal pressure. The spin alignments of Fe initially lie parallel inside the basal plane and then turn spirally between adjacent layers with a zone axis along the c direction under higher Lu concentration. The synchrotron and neutron powder diffraction investigations clearly reveal that the direction of spin alignments is highly correlated to large lattice contraction induced by negative thermal expansion (NTE), an unusual thermal pressure, along the c direction. The critical lattice parameter c to form spiral spin alignments is determined unambiguously. This work presents a feasible way to adjust spin alignments through NTE, which might be conducive to the future design of particular spin alignments instead of physical pressure for functional magnetic materials.

Modified screening interaction potential on dust lattice waves in dusty plasma ring

In the present paper, the modified screening interaction potential was adopted to investigate the dust lattice waves in dusty ring. Firstly, the influence of parameter ε on the modified screening interaction potential was analyzed; and it was found that the parameter ε has a long-range effect on the pairwise interaction between the particles. Secondly, the dispersion relations of longitudinal and transverse waves are obtained, and the effect of long-range action parameter ε, dimensionless lattice parameter α and dimensionless shielding parameter on the dust lattice waves propagation in dusty ring are studied. Some interesting phenomena, such as the coupling of longitudinal and transverse waves, and instabilities of transverse waves are found, which are in good agreement with some previous works. Finally, the transverse wave instabilities and the relevant critical lattice parameter αc are presented and discussed.

Nonlinear intraband tunneling of a Bose-Einstein condensate in a cubic three-dimensional lattice

The intraband tunneling of a Bose-Einstein condensate between three degenerate high-symmetry $X$ points of the Brillouin zone of a cubic optical lattice is studied in the quantum regime by reduction to a three-mode model. The mean-field approximation of the deduced model is described. Compared to the previously reported two-dimensional (2D) case [V. S. Shchesnovich and V. V. Konotop, Phys. Rev. A 75, 063628 (2007)], which is reducible to the two-mode model, in the case under consideration there exist a number of new stable stationary atomic distributions between the $X$ points and a new critical lattice parameter. The quantum collapses and revivals of the atomic population dynamics are absent for the experimentally realizable time span. The 2D stationary configurations, embedded into the 3D lattice, turn out to be always unstable, while the existence of a stable 1D distribution, where all atoms populate only one $X$ state, may serve as a starting point in an experimental study of nonlinear tunneling in a 3D lattice.

Electronic and Magnetic Properties of AlFe3 and AlFe3N Nitride

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electronic and magnetic properties of AlFe3 and AlFe3N nitride

Self-consistent band structure calculations were performed for the metal aluminide AlFe3 (in the fcc structure) and the nitride AlFe3N (perovskite-like nitride) at several lattice parameters in order to obtain the electronic structure and magnetic properties of these compounds. In this study we have employed the full potential linear augmented plane wave (FPLAPW) and the linear muffin-tin orbital (LMTO-ASA) methods. Our results show that the modeled AlFe3 is ferromagnetic (FM) with 2.07μB as the magnetic moment at Fe sites. On the other hand, AlFe3N is non-magnetic (NM) contrary to other perovskite nitrides that show magnetic order. Hence as the stable phase of AlFe3 is magnetic with DO3 structure a crystallographic transformation occurs accompanied by a magnetic transition from a non-magnetic perovskite structure to a magnetic DO3 structure as AlFe3N lose nitrogen atoms. The LMTO and FPLAPW total energy calculations give the equilibrium volume for both compounds. For AlFe3N, the FPLAPW calculations give the equilibrium volume that agrees well with the experimental lattice spacing, which is not achieved by LMTO calculations within the same accuracy. The calculated magnetic moment as function of the lattice parameter for the AlFe3 shows a collapse of the magnetism at certain critical lattice parameter whose FPLAPW value (2.962Å) differs only slightly from the LMTO value (3.041Å).

Magnetic and electronic structure of Ni/Ag bilayers

Self-consistent band-structure calculations were performed for Ni/Ag bilayers to study important features of these materials. Using the Linear Muffin-Tin Orbital (LMTO) method, we carried out calculations for several lattice parameters in order to obtain ground-state properties such as equilibrium volume, bulk modulus and critical pressure of the Ni/Ag bilayers. The analysis of the density of states at equilibrium volume gives a good description of the electronic and magnetic properties of these bilayers. The results show a breakdown of the small magnetic moment at Ni sites for certain critical lattice parameters.

Transition metal monolayer or bilayer: ferromagnetism versus lattice parameter

Within a tight-binding scheme, monolayer and bilayer ferromagnetism is investigated. We determine the possible values of the magnetic moment versus the band filling. We point out the importance of first-order transition from a para- to ferro-magnetic state. For this reason, a large range of magnetic moment values is excluded. If only “s” bands are considered, the forbidden magnetic moment areas are limited. For systems with “d” bands, the possible values are very restricted and saturated ferromagnetism is often present. A systematic study for transition metals is presented and the critical lattice parameter for the onset of ferromagnetism is discussed. Good agreement with available experimental data is obtained.

Pressure dependence of Ms- T curve in GdMn 2

Measurements of magnetization vs temperature curves under pressures have been made in GdMn 2 intermetallic compound up to a hydrostatic pressure of 10.7 kbar and a chemical pressure of 14.8 kbar in the low temperature region between 4.2 and 150 K, and the pressure dependence of the Néel temperature of the Mn-sublattice was determined. By using data for the pressure dependence of the lattice parameter, the critical pressure of 14.8 kbar, below which the Mn sublattice magnetic moment disappears, was converted to the critical lattice parameter of 7.6Å. This value is in excellent agreement with the results of Yoshimura et al.

Impurity doping effects in V2O3

Abstract The electrical properties of (MxV1–x)2O3 (M = A1, Cr, Fe, Ga, Rh, Ti) have been investigated. Only Al- and Cr-doped V2O3 exhibit electrical transitions close to room temperature. X-ray diffraction shows that no critical lattice parameter can be identified to correlate with the occurrence or absence of this transition. Some features are described which cannot readily be reconciled with existing theories of the metal-insulator transition.

Flux-Line Arrangement in Superconductors as Revealed by Direct Observation

The flux-line lattice in a type-II superconductor in the remanent state is investigated by means of a decoration method. The triangular lattice contains various kinds of defects, the most important of which are flux-line dislocations. A critical lattice parameter dc exists such that for lattice parameters d>dc the flux lines form no longer a lattice but a ``flux-line fluid.'' A belt directly underneath the specimen surface is free from flux lines. The transition from the ``fluid'' to the flux-free region has been utilized to estimate in a fairly direct way the pinning forces acting on the flux lines.

X-Ray and Susceptibility Study of the First-Order Magnetic Transformation in Mn3Pt

The first-order transformation from triangular to collinear antiferromagnetic structure (AF-AF transformation) has been investigated in the Mn3Pt1−xRhx and Mn3+yPt1−y systems by x-ray diffraction and magnetic methods. At the AF-AF transformation temperature Tt a discontinuous change in the lattice parameter is observed with a magnitude depending on concentration but with always the same lattice parameter value of the collinear phase. This implies the existence of a critical lattice parameter value for the AF-AF transformation. Below the Néel temperature TN an anomaly in the thermal expansion occurs indicating exchange interactions dependent on the interatomic separation. This anomaly differs in sign for the collinear-paramagnetic and triangular-paramagnetic transitions. The susceptibility shows an abrupt change at Tt and a maximum at TN in the triangular phase. No maximum occurs for the collinear phase. The observed transition temperatures are in agreement with the earlier neutron diffraction data.