Mössbauer studies on the series La1-xSrxFeO3

Mössbauer spectra have been recorded at 4.2 and 300 K on the series La_1–x Sr _x FeO₃, wherex varies from 0 to 1.0 in steps of 0.1. Neutron diffraction experiments have shown that the crystal structure is orthorhombic for 0x<0.3, rhombohedral for 0.4x0.7, and cubic for 0.8<x1.0. Mössbauer spectra at 4.2 K are composed of magnetic sextet components arising from different charge states of iron ions. In the orthorhombic and rhombohedral phases, the charge states Fe³⁺ and Fe⁵⁺ coexist. In the cubic phase, iron is present as Fe³⁺ and Fe⁴⁺ states. At 300 K, the samples are magnetically ordered in the range 0 x0.3 and the coexistence of Fe³⁺ and Fe⁵⁺ remains. For samples 0.4x1.0, the samples are paramagnetic. Fits to these spectra require two components, one corresponding to an Fe⁴⁺ state, the other being best described as an Fe³⁺ ion forx0.7 but forx>0.7 having a mean charge state which increases to 3.5 forx=1.0.     

Mössbauer study of mixed valent silicides Eu(Ir1−x Pd x )2Si2

The solid solutions Eu(Ir_1–x Pd _x )₂Si₂, which exist for 0x0.125 and 0.75x1. cristallize with the tetragonal ThCr₂Si₂-type structure. The variation of the europium valence with composition has been thoroughly studied at temperatures 4.2T293 K by¹⁵¹Eu Mössbauer resonance. For 0x0.125 the europium valence at room temperature decreases asx increases. For 0.75x1 the valence transition temperature Eu³⁺Eu²⁺ increases asx increases.     

Zeros of the finite-size scaling region partition function for a model with a wetting transition

We derive a finite-size scaling representation for the partition function for an Onsager-Temperley string model with a wetting transition, and analyze the zeros of this partition function in the complex scaled coupling parameter of relevance. The system models the one-dimensional interface between two phases in a rectangular two-dimensional region (x, y) ²,–L yL,oxN. The two phases are at coexistence. The string or interface has a surface tension 2KkT per unit length and an extra Boltzmann weighta per unit length if it touches the surfaces aty=±L. There is a critical valuea _c=1/2K and fora>a _c the string is confined to one of the surfaces, while fora a _c the string moves roughly in the rectangular region. The finite-size scaling parameters are =a _c ² N/L ² and =L(a–a _c)/a _c ² . We find that for || large, the zeros of the scaled partition function lie close to the lines arg()=±/4 with re()>0. We discuss the motion of all the zeros as changes by both analytic and numerical arguments.     

How often do simple dynamical processes have infinitely many coexisting sinks?

This work concerns the nature of chaotic dynamical processes. Sheldon Newhouse wrote on dynamical processes (depending on a parameter )x _x+1=T(x _n ; ), wherex is in the plane, such as might arise when studying Poincaré return maps for autonomous differential equations in IR³. He proved that if the system is chaotic there will very often be existing parameter values for which there are infinitely many periodic attractors coexisting in a bounded region of the plane, and that such parameter values would be dense in some interval. The fact that infinitely many coexisting sinks can occur brings into question the very nature of the foundations of chaotic dynamical processes. We prove, for an apparently typical situation, that Newhouse's construction yields only a set of parameter values of measure zero.This research was supported in part by grants from the Air Force Office of Scientific Research AFOSR 81-0217, the Consiglio Nazionale delle Ricerche-Comitato per le Matematiche, and the National Science Foundation DMS 84-19110On leave from: Dipartimento di Matematica G. Castel nuovo Universita di Roma La Sapienza P. le Aldo Moro 5, I-00185 Rome, Italy     

Mössbauer study of the perovskite series Sr(Fe1−xTix)Oy

⁵⁷Fe Mssbauer effect in the perovskite series Sr(Fe_1–xTi_x)O_y (0.0x0.99; y3) at RT and 78K has been analyzed. The influences of the Ti composition on the coexitence of Fe⁴⁺ and Fe³⁺, the ratio of Fe⁴⁺ to the total Fe, and the Y value have been studied. When 0x0.6 the ratio of Fe³⁺ (II) doublet to the total Fe increases as the final firing temperature increases, agreeing with the result obtained from the positron lifetime measurements. When x0.7, the Fe³⁺ (II) doublet disappears. In the range of x=0.9 and x=0.99, there still exists a considerable content of Fe⁴⁺ in samples, disagreeing with the result obtained from the chemical analysis by Clevenger. The relations between the electrical resistivity and the thermistor material constant B of negative temperature characteristic varying with Ti composition have been discussed.     

Evidence of Hg-chain formation in Hg x TiS2: a199mHg-TDPAC study

We determined the^199mHg nuclear quadrupole interaction in the misfit or superstoichiometric compound Hg _x TiS₂ by time differential perturbed angular correlation. A unique Hg-site withv _Q =511(1) MHz and =0.410(4) was observed, irrespective of the Hg-uptake (2/3x4/3). We propose a model of Hg-Hg zig-zag chains which accounts for these observations as well as for the X-ray diffraction data.     

Magnetic Study of Doped Ba Ferrites Prepared by Citrate Method

The M-type barium ferrite is doped with either Co²⁺-Ti⁴⁺ or Co²⁺-Zr⁴⁺ pairs to reduce its intrinsically high uniaxial magnetic anisotropy in order to make fine particles for magnetic recording. The magnetic parameters were investigated by magnetic measurements and the Mössbauer spectroscopy. Compounds (BaF) obtained from BaCo _x (Ti,Zr) _x Fe_12-2x O₁₉ with 0x1.0 have been prepared by the modified citrate method with the initial ratio of Ba:Fe equal to 1:10.8. The substitution of Co - Ti or Co - Zr for Fe³⁺ ions affects mainly the positions 2a and 4f ₂. Ba ferrite with the substitution x 0.8 is promising for perpendicular recording media applications.     

Stimulated IR- and vacuum-UV emission following two-photon-excitation of molecular hydrogen using an ArF laser

Hydrogen molecules are excited by two 193 nm-photons [X¹ _g ⁺ E,F¹ _g ⁺ ;Q₀₂(1)] generated with a commerical oscillator-amplifier ArF laser. Stimulated emission is subsequently observed in the IR (=752.4 nm to 836.6 nm;E, FB) and in the VUV (=134.0 nm to 160.9 nm;BX) with a VUV conversion efficiency of 0.2%. The rotational fine-structure, the saturation behaviour, pump depletion as well as SRS-onset on and off two-photon resonance are investigated.     

Magnetic states of Cu1 sublattice in YBa2Cu3Oy high Tc compounds at different oxygen content

Magnetic states of Cu1 sublattice in YBa₂Cu₃O _y : 1%⁵⁷Fe compounds with 6.09 y6.98 were investigated by⁵⁷Fe Mössbauer spectroscopy at 1.68T300 K. It has been found that, upon reducingy, the magnetic transition temperatureT _ml changes from 3.3 to 12 K aroundy6.4 where the superconductivity disappears. The magnetic phase diagram for the Cu1 sublattice is plotted.     

Mössbauer and magnetization studies on the ferromagnet Fe3−x Ru x Si

⁹⁹Ru and⁵⁷Fe Mössbauer spectroscopic studies were carried out on ternary intermetallic compounds containing ruthenium, Fe_3–x Ru _x Si, within the concentration range 0.1x1.5. Magnetization of the samples was also measured in the temperature range between 4 K and room temperature.⁹⁹Ru Mössbauer spectra ofx=0.5 and 1.0 were fitted satisfactorily with a broad component ofH _hf, the peak positions of which were 340 and 270 kOe, respectively.     

Investigation of conductivity in the Sr(Fe1−xTix)Oy system by iron-57 Mössbauer spectroscopy

On the basis of our previous work electrical conductivity in the Sr(Fe_1–xTi_x)O_y system (0.0x0.9,y3) has been further studied by means of Mössbauer spectroscopy. When 0.0x0.6, the concentration of Fe³⁺ (II) doublet relates to the final firing temperature and electrical conductivity of the materials is sensitive to the concentration of Fe³⁺ (II). Atx=0.25, the curve of the resistivity versus Ti contentx shows a local minimum which is observed for the first time. The results indicate that the coexistence of Fe⁴⁺ and Fe³⁺ in the same lattice leads to high conductivity; the conductivity increases when the Fe⁴ concentration approaches to that of the Fe³⁺ one. When the temperature is at 260 K and 230 K, the presence of the intermediate state showing quadrupole splitting has an effect on the conductivity of the materials.     

Structural and optical properties of ZnSe x Te1−-x solid solutions in thin-film form

Solid solutions of ZnSe _x Te_1–x (0. 1 x 1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc-blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fractionx following Vegard's law:a(x) = 6.165 – 0.485x. Thin films of ZnSe _x Te_1–x (0.1 x 1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10^–4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe _x Te_1–x polycrystalline films of different compositions have two direct transitions with corresponding energy gapsE _g andE _g + _so The variations in bothE _g andE _g + _so, withx indicate that ZnSe _x Te_1–x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.     

Inequalities for the Schattenp-norm. III

We present some inequalities for the Schattenp-norm of operators on a Hilbert space. It is shown, among other things, that ifA is an operator such that ReAa0, then for any operatorX, AX+XA* _p 2aX _p . Also, for any two operatorsA andB, A–B ₂ ² +A*B* ₂ ² 2A–B ₂ ² .     

Electrical and magnetic properties of solid solutions of iron and manganese monosilicides

The features of the energy spectra of the solid solutions Fe_1–xMn_xSi (0 x 1) are discussed on the basis of an experimental study of the concentration and temperature dependences of the electrical resistance, the Hall constant, the thermal emf, and the magnetic susceptibility.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 3, pp. 74–79, March, 1969.     

Temperature dependence of the electric field gradient in Er metal

The method of perturbed angular distributions was used to measure the temperature dependence of the electric field gradient in Er single crystal for 98 KT156 K. The I=11^– isomer in Er¹⁵⁴) was used as a probe. ₀ increases monotonically for 98 KT259 K and then decreases. A possible cause for this effect may be short range interactions between the f electrons above the Neel point.Visitor from the Weizmann Institute, Rehovoth, Israel.     

Structural transformations in MoO<Subscript>x</Subscript> thin films grown by pulsed laser deposition

In this work, laser-induced crystallization in MoO_x thin films (1.8x2.1) is reported. This transformation involves a MoO_x oxidation and subsequently a crystallization process from amorphous MoO₃ to crystalline MoO₃. For comparison purposes crystallization is induced thermally, in an oven, as well. The crystallization kinetics is monitored by Raman spectroscopy; a threshold in the energy density necessary to induce the phase transformation is determined in the case of photo-crystallization. This threshold depends on the type of substrate on which the film is deposited. For the thin films deposited on glass substrates, the structural transformation is from amorphous MoO_x to the thermodynamically stable MoO₃ crystalline phase. For the thin films deposited on Si(100) the structural transformation is from amorphous MoO_x to a mixture of MoO₃ and the thermodynamically unstable MoO₃ crystalline phases. The structural transformations are also characterized by scanning electron microscopy and light-transmission experiments. PACS 81.15.Fg; 61.80.Ba; 78.30.-j     

Magnetic Properties of Permalloy/Cu-Au Multilayers

The interlayer exchange coupling and GMR effect of (permalloy/Cu _x Au_1-x )30 (Py = Ni₈₃Fe₁₇; 0.29x0.75) sputtered multilayers (MLs) were investigated. The strength of the antiferromagnetic (AF) interlayer coupling J _AF was determined from M(H) and/or R(H) curves. GMR effect and AF coupling was found in entire investigated concentration range of Cu _x Au_1-x . For x<0.65 the J _AF values at the first maximum of AF coupling (1.3t _Cu-Au1.6 nm) were smaller than 3×10^-6 J/m² and for x>0.65 J _AF increased to a value characteristic of Py/Cu MLs (J _AF10^-5 J/m²). The second maximum of AF coupling (J _AF10^-7 J/m²) was only found for x0.75 at t _Cu-Au2.6 nm.     

155Gd Mössbauer investigation on (GdxNd1−x)1+εFe4B4

Tetragonal (Gd_xNd_1–x)₁₊ Fe₄B₄ alloys have been investigated for 0.2x1 by Mössbauer spectroscopy, using the 86.5 keV¹⁵⁵Gd resonance. The Gd quadrupolar interaction e²qQ=12.67(5) mm/s for x=1, nearly independent of x, is the largest observed to date in metallic compounds of Gd. A crystal field term A ₂ ⁰ =–2450±50 K/a ₀ ² is inferred. This quadrupolar interaction shows some dispersion increasing when x decreases, reflecting the quasi incommensurate nature of the (Gd,Nd) and Fe+B sublattices in the (Gd_xNd_1–x)Fe₄B₄ structure (=0.109 for x=0 and =0.139 for x=1). The hyperfine field is perpendicular to the c axis for x0, but no unique direction is obtained for x=0.     

BRST quantization of a scalar particle in a curved background

The BRST formalism is employed to quantize a scalar particle and interactions with an external scalar field (x ) and vector gauge fieldA (x ) in the background of an arbitrary gravitational field. The second-quantized actions are obtained.     

Ballistic annihilation and deterministic surface growth

A model of deterministic surface growth studied by Krug and Spohn, a model of the annihilating reactionA+Binert studied by Elskens and Frisch, a one-dimensional three-color cyclic cellular automaton studied by Fisch, and a particular automaton that has the number 184 in the classification of Wolfram can be studied via a cellular automaton with stochastic initial data called ballistic annihilation. This automaton is defined by the following rules: At timet=0, one particle is put at each integer point of . To each particle, a velocity is assigned in such a way that it may be either +1 or –1 with probabilities 1/2, independent of the velocities of the other particles. As time goes on, each particle moves along at the velocity assigned to it and annihilates when it collides with another particle. In the present paper we compute the distribution of this automaton for each timet . We then use this result to obtain the hydrodynamic limit for the surface profile from the model of deterministic surface growth mentioned above. We also show the relation of this limit process to the process which we call moving local minimum of Brownian motion. The latter is the processB _x ^min ,x , defined byB _x ^min min{B _y ;x–1yx+1} for everyx , whereB _x ,x , is the standard Brownian motion withB ₀=0.