The structures and magnetic properties of Cr/Fe and Mn/Fe thin films

Cr_1-x Fe _x and Mn_1-x Fe _x films were prepared at room temperature by thermal coevaporation at a deposition rate of about 25 Å/min. It was found that an amorphous phase can be obtained for Cr_1-x Fe _x (0.25<x<0.60) films, while a metastable-Mn-type phase was observed for Mn_1-x Fe _x (x<0.70) films. The influence of the structure on the magnetic properties has been studied. The amorphization ability of the two systems was discussed in terms of thermodynamic considerations.     

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.     

The transverse correlation length for randomly rough surfaces

It is shown by numerical simulations for a random, one-dimensional surface defined by the equationx ₃=(x ₁), where the surface profile function (x ₁) is a stationary, stochastic, Gaussian process, that the transverse correlation lengtha of the surface roughness is a good measure of the mean distance d between consecutive peaks and valleys on the surface. In the case that the surface height correlation function (x ₁)(x ₁)/²(x ₁)=W (|x ₁–x ₁|) has the Lorentzian formW(|x ₁|)=a ²/(x ₁ ² +a ²) we find that d=0.9080a; when it has the Gaussian formW(|x ₁|)=exp(–x ₁ ² /a ²), we find that d=1.2837a; and when it has the nonmonotonic formW(|x ₁|)=sin(x ₁/a)/(x ₁/a), we find that d=1.2883a. These results suggest that d is larger, the faster the surface structure factorg(|Q|) [the Fourier transform ofW(|x ₁|)] decays to zero with increasing |Q|. We also obtain the functionP(itx ₁), which is defined in such a way that, ifx ₁=0 is a zero of (x ₁),P(x ₁)dx ₁ is the probability that the nearest zero of (x ₁) for positivex ₁ lies betweenx ₁ andx ₁+dx ₁.     

A Statistical Theory of Dipole Ordering in Solid Solutions of ADP- and KDP-Crystals with the H22 Structure

A theory of dipole ordering in solid solutions of isomorphic ferro- and antiferroelectrics with the H₂₂ structure is developed. Free energies and thermodynamic potentials of the systems are calculated. Equilibrium conditions are studied. The Curie temperatures for phase transitions are found. The K_1–x (NH₄)_xH₂PO₄, M_1–x M_xH₂PO₄ (M, M = K, Rb, Cs), and (NH₄)_1–x Tl_xH₂PO₄ are examined. The temperature dependence of the shear modulus and dielectric constant in the vicinity of the point of phase transition is estimated for dihydrophosphate potassium ammonate. The calculation results are compared with experiment.     

High-resolution electron microscopy and electron diffraction on Bi2Sr2-x La x Ca n Cu1+n O6+2n+δ

Solid solutions, Bi₂Sr_2-x La _x CuO₆₊ withx< 1.3 and Bi₂Sr_2-x La _x CaCu₂O₈₊ with probablyx<1.3 are reported. Both solid solutions show considerable nonlinear changes in the unit cell dimensions and a change in the modulation vector from 4.7b to 3.5b forx=0 andx=1.2, respectively. It is shown that Bi₂Sr_2-x La _x CaCu₂O₈₊ shows sometimes the absence of the 0.54 nm period alonga, whereas the modulation remains, suggesting both features not to be correlated. The investigation of the solid solution Bi₂Sr_2-x La _x CaCu₂O₈₊ with probablyx<1.3 are reported. Both solid solutions show considerable nonlinear changes in the unit cell dimensions and a change in the modulation vector from 4.7b to 3.5b forx=0 andx=1.2, respectively. It is shown that Bi₂Sr_2-x La _x CaCu₂O₈₊ is severly hampered by the presence of the n=0 structure in the reaction product when one starts with stoichiometric mixture. This can be overcome by adding extra Ca and heating directly just below the melting point. However addition of Ca to the mixture leads to changes in the solid solution range, because Ca can replace Sr.     

Properties of certain matrices related to the equilibrium configuration of the one-dimensional many-body problems with the pair potentialsV 1(x)=−log ∣sinx∣ andV 2(x)=1/sin2 x

It is shown that at equilibrium certain matrices associated to the one-dimensional many-body problems with the pair potentialsV ₁(x)=–logsinx andV ₂(x)=1/sin² x have a very simple structure. These matrices are those that characterize the small oscillations of these systems around their equilibrium configurations, and, for the second system, the Lax matrices that demonstrate its integrability.     

On the role of theΔ -isobar in deep inelastic scattering on the deuteron

The role of the nuclear structure effects, viz. the boundness of nucleons and-isobar components, in the deep inelastic scattering of leptons on the deuteron is considered. It is shown that small admixture of the-isobar configurations to the deuteron wave function may lead to significant effects in the spin structure functions of the deuteronb ₁ ^D andg ₁ ^D (x): up to 4% in g ₁ ^D (x) dx and up to 10% ing ₁ ^D (x) at smallx.One of the authors (A.U.) thanks Prof. F.C. Khanna for helpful discussions and for kind offering the information used in our calculations.     

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.     

Specific Features of Scattering by Spin Fluctuations and the Electronic Structure of Weak Band Semiconducting and Semimetal Magnets

The effect of scattering by spin fluctuations on the electronic structure of weak band semiconducting and semimetal magnets is examined, in particular, the feasibility of origin of the Anderson localized states. The results obtained are analyzed on the example of the FeSi nearly ferromagnetic semiconductor and (FeSi)_1–x (CoSi) _x weak band semimetal magnets with x 0.05.     

Rare-earth iron-based intermetallic compounds and their carbides: Structure and magnetic behaviors

The structural and magnetic properties of Sm₂Fe_17-xMo_x, its out of equilibrium precursor SmFe_9-yMo_y and their carbides are investigated by means of powder X-ray diffraction, magnetic measurements and high-resolution transmission electron microscopy. The structure of the nanocrystalline Sm_1-s(Fe,Mo)_5+2s alloys are governed by the s Sm vacancy rate and the x amount of Mo. In this work, the Rietveld analysis shows that for s=0.33 the structure is of Th₂Zn₁₇-type and P6/mmm with the stoichiometry 1/9 for s=0.36. Moreover, it points out a lattice expansion along the c-axis after Mo substitution for Fe and reveals a 6c preferential occupation for Mo atoms in structure, and 2e for the out of equilibrium hexagonal precursor. Upon carbon insertion, the lattice expansion favors the Curie temperature increase up to 35% for Sm₂Fe_16.42Mo_0.58C₂ and 49% for the metastable SmFe_8.7Mo_0.3C carbide. The Curie temperature and the coercive field of the 1/9 carbides are higher than those of 2/17 ones. This makes the out of equilibrium hexagonal precursor a competitive candidate for use as permanent magnet.     

Valence change of europium in the Eu(Ir1−x Pd x )2Si2 silicides

Eu(Ir_1–x Pd _x )₂Si₂ solid solutions which exist only for 0x0.125 and 0.75x1 crystallize in the tetragonal ThCr₂Si₂-type structure. X-ray diffraction data, magnetic susceptibility and¹⁵¹Eu Mössbauer measurements suggest that these compounds can be characterized as homogeneous mixed valence systems. At room temperature and for 0x0.125, the europium valence decreases asx increases. For 0.75x1, a sharp continuous valence transition from Eu²⁺ to Eu³⁺ occurs near 48 K, 54 K and 78 K forx=0.75, 0.81 and 0.94 respectively. These valence changes are discussed in relation with the Eu–(Ir, Pd) interatomic distance.     

The structure of ‘nearly’ ferroelectric RADP

X-ray scattering techniques have been used to study the structures of two crystals of Rb_1–x (NH₄) _x H₂PO₄ withx0.2, near to the boundary between ferroelectric and structural-glass behavior at low temperature. Below about 83K, both crystals develop shortrange incommensurate correlations with a wavevectorq0.13 a ^* which are presumably related to the glass properties. On cooling below 70 K, the crystal with the slightly larger NH ₄ ⁺ concentrationx, develops the ferroelectric structure in a small fraction of the crystal, while the bulk of the crystal retains the tetragonal structure. The other crystal transforms almost wholly to the ferroelectric phase. The transition to the ferroelectric structure shows considerable hysteresis on heating and cooling, and is spread over about 20 K. The transition is certainly of first order, and the spread in temperature may arise from concentration fluctuations. These results and the structure of the incommensurate modulations are compared with the predictions of a theoretical model for this system.     

A Structural,Magnetic and Mössbauer Study of Tb0.3Dy0.7(Fe1−x Al x )1.95 Alloys

A structural, magnetic and Mössbauer study of a series of Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys (x=0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature is presented. It was found that the primary phase of the Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys is the MgCu₂-type cubic Laves phase structure when x<0.3 and a small amount of a second phase, RFe₃ (R: rare-earth element), is present when 0.3x0.35. The lattice constant of the Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys increases approximately monotonically with increasing x. The substitution of Al increases slightly the magnetostriction in a low magnetic field (H500 Oe). However, the magnetostriction decreases sharply, but is saturated more easily with increasing x in a higher applied field. The analysis of the Mössbauer spectra allows the determination of the easy axes of magnetization in these alloys. Moreover, the dependence of the hyperfine-field, isomer shift and quadrupole splitting on the Al concentration, x, for the Tb_0.3Dy_0.7(Fe_1–x Al _x )_1.95 alloys are reported and discussed.     

Self assembled nanoparticle Pb1−xFexSe/single crystal Si heterojunctions

Nanoparticle Pb_1−xFe_xSe (0.00  x  0.16) thin films have been deposited on quartz, glass and silicon substrates by chemical bath deposition technique. Structural and optical properties of the films with iron concentration 0.00  x  0.16 indicate that the films grow as single-phase Pb_1−xFe_xSe ternary alloys with rocksalt structure and with direct optical band gaps (E_g) that increase with decrease in grain size and have values larger than 0.28 eV of the bulk PbSe. Average grain size in films grown at fixed bath temperature T_b of 85 °C is observed to decrease from 72 to 22 nm whereas lattice parameter is observed to increase from 6.12 to 6.14 Å with increase in Fe concentration from x = 0.00 to x = 0.16. The observed blue shift in film materials originates from quantum confinement in the nanograins. Nanoparticle Pb_1−xFe_xSe/single crystal Si heterojunctions show rectifying behavior. On illumination of heterojunctions with visible light current is observed to increase in forward and reverse bias. This increase in current in the presence of visible light is considered to be due to carrier multiplication by Auger electron emission.     

The Peierls transition of Perylene radical cation salts with 2:1 stoichiometry containing tetrahydrofuran

Crystal structure, microwave conductivity and static magnetic susceptibility were analyzed for the conducting perylene (PE) radical cation salts of nominal composition (PE)₂(PF₆)_1–x (AsF₆) _x ·2/3 THF for 0x1. Crystallographic phase transitions in the high-temperature metal phase were also characterized by differential scanning calorimetry and electron spin resonance. The Peierls transition occuring at 100–120 K (depending onx) and the opening of the energy gap in the semiconductor phase were determined from the magnetic data. The dependence of these properties on the size of the complex anions and the packing of the PE molecules is discussed.     

Phase diagrams and magnetic properties of diluted Ising and Heisenberg magnets with competing interactions

Ising and Heisenberg magnets with nearest-neighbor ferromagnetic exchangeJ ₁ and next-nearest antiferromagnetic exchangeJ ₂ and randomly distributed frozen-in nonmagnetic impurities of arbitrary concentration 1–x are studied by several methods: systematic series expansions inx, 1–x and inverse temperature (1/T) as well as Monte Carlo simulation. Depending onRJ ₂/J ₁,T andx the model is in paramagnetic, ferromagnetic, antiferromagnetic or spin glass phases. The microscopic magnetic structures of all these phases are investigated and found to be more complicated than usually (e.g., the ferromagnetic state contains spins and clusters either aligned antiparallel or not aligned at all, when frustration effects make bonds ineffective). We suggest that the concentrationx _c of magnetic ions below which no (anti-)ferromagnetic long range order occurs depends onR continuously, andx _c 1 at the multicritical point (R _m ,T=0) where the order changes from ferromagnetic to antiferromagnetic. Our results for phase diagram, susceptibility etc. are compared to recent data on the Eu _x Sr_1–x S system and very good agreement is found.     

On the magnetic susceptibility of the liquid Pd1−x Si x alloy system at 1825 K

The isothermal magnetic susceptibility (x) of the completely miscible liquid Pd_1–x Si _x alloy system shows a rapid monotonous decrease withx from strong paramagnetism to weaklyx-dependent diamagnetism. The measured susceptibility isotherm at 1825 K is analysed within 0x1 by using a semiphenomenological method of decomposing the magnetic susceptibility into its constituent parts. Because of the empirical similarity between liquid and glassy metals this interpretation also provides assertions about the magnetism of glassy Pd_1–x Si _x aroundx=0.2.     

Blue cathodoluminescence from thulium implanted AlxGa1−xN and InxAl1−xN

Room temperature cathodoluminescence (RTCL) was obtained from Tm implanted Al_xGa_1−xN with different AlN contents (in the range 0≤x≤0.2) and from implanted In_xAl_1−xN with different InN contents (x=0.13 and 0.19) close to the lattice match with GaN. The Tm³⁺ emission spectrum depends critically on the host material. The blue emission from Al_xGa_1−xN:Tm peaks in intensity for an AlN content of x0.11. The emission is enhanced by up to a factor of 50 times with an increase of annealing temperature from 1000 to 1300 C. The blue emission from In_0.13Al_0.87N:Tm, annealed at 1200 C, is more than ten times stronger than that from Al_xGa_1−xN:Tm, x≤0.2. However, the intensity decreases significantly as the InN fraction increases from 0.13 to 0.19.     

Positron annihilation studies on the electronic structure of Pd−Ag−H system

Angular Correlation of Annihilation Radiation (ACAR) is shown to be useful to examine the electronic structure of -phase Pd_1–y Ag _y H _x system. Hydrogen absorption by Pd_1–y Ag _y alloys results in the increase of both nearly free andd-localized electron numbers in compliance with the KKR-CPA calculation outcomes. The investigation of -phase systems, PdH _x hydrides as well as Pd_1–y Ag _y H _x materials, failed because of a high concentration of lattice defects.