Mesoscopic magnetic inhomogeneities in the low-temperature phase and structure of Sm1−x SrxMnO3 (x < 0.5) perovskite

Results are presented of studies of the ¹⁵⁴Sm_1?x Sr_xMnO₃ system using neutron powder diffraction and small-angle polarized neutron scattering. An analysis of the neutron diffraction spectra showed that at T < 180 K these exhibit typical Jahn-Teller distortions of the manganese-oxygen octahedrons which persist under further cooling and on transition of the sample to a metallic magnetically ordered state. The magnetic contribution to the diffraction is satisfactorily described using the (A _x (A _y )F _z ) model and is interpreted as the coexistence of ferromagnetic and antiferromagnetic phases. The exaggerated widths of the diffraction lines indicate an appreciable contribution from microdeformations evidently associated with the inhomogeneity of the system. Small-angle polarized neutron scattering showed that the Sm system for x = 0.4 and 0.25 is magnetically inhomogeneous in the low-temperature phase. Ferromagnetic correlations occur on scales of around 200 Å and having dimensions greater than 1000 Å which, combined with the temperature hysteresis of the magnetic small-angle scattering intensity observed for an x = 0.4 sample in the low-temperature phase, suggests that the transition is of a percolation nature.     

Inhomogeneous lattice distortions in a Zn1 − x CrxSe crystal

The structure of a Zn_1?x Cr_xSe semiconductor crystal with x = 0.0029 was studied using thermal neutron diffraction. It was detected that the diffraction patterns of the crystal contain regions of diffuse scattering concentrated in the vicinity of the strong Bragg reflections. It was shown that the diffuse scattering was caused by transverse displacements of lattice atoms induced by chromium impurities, which undergo static tetragonal Jahn-Teller distortions in ZnSe.     

Neutron crystal-field spectroscopy and susceptibility in TmxY1−xAl2

Inelastic neutron scattering due to crystalline electric field transitions is observed in Tm_0.25Y_0.75Al₂. The best fit of the theoretical cross section to experiment is obtained for the Lea, Leask and Wolf parameters W = (0.040 ± 0.005)meV and X = (0.50 ± 0.05). The extrapolation of the measured susceptibility of Tm_xY_1?xAl₂(x = 0.05, 0.15, 0.25)tox = 0 is in good agreement with theory when using the above parameters.     

Nanoscale distortions of the lattice of a ZnSe crystal doped with 3d elements

The structure of semiconductor crystals Zn_1?x V _x ²⁺ Se (x = 0.0018) and Zn_1?x Cr _x ²⁺ Se (x = 0.0006) was studied for the first time using thermal neutron diffraction at 300 and 120 K. The diffraction patterns of the crystals were revealed to contain diffuse scattering regions near the Bragg reflections of the initial cubic lattice. The experimental results are discussed in combination with earlier obtained data on neutron diffraction and propagation of ultrasonic waves in Zn_1?x Ni _x ²⁺ Se (x = 0.0025) and Zn_1?x Cr _x ²⁺ Se (x = 0.0029). The diffuse scattering is shown to be due to nanoscale shear strains of the ZnSe lattice. The character of these strains is determined by Jahn-Teller 3d ions.     

Structural deformations of the cubic lattice of the Zn1 ? x Fe x Se (x = 0.001) crystal

The structural state of a Zn_{1 ? x} Fe _x Se (x = 0.001) crystal has been studied using thermal neutron diffraction. The diffraction patterns of the cubic crystal have been found to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It has been shown that the diffuse scattering effects are due to local transverse displacements of the crystal lattice atoms, and these displacements are induced by iron ions that demonstrate the static Jahn-Teller effect of the tetragonal type in the ZnSe compound.     

Spin waves in Fe3−xMnxSi ordered alloys

Spin wave dispersion relations in Fe_3?xMn_xSi ordered alloys have been measured by neutron scattering for alloys with x = 0.04 and x = 0.18. The dispersion relations have been found to be quadratic in the magnon wavevector q? up to about half of the Brillouin zone along [111] direction. The measured values of the spin wave stiffness constant are 169±7 meV Å⁰² and 207±7 meV Å⁰² for samples with x = 0.18 and x = 0.04, respectively. The energy gap found from the rough data turned out to be almost totally due to the triple-axis spectrometer resolution properties. The nearest neighbour exchange integral for FeFe interaction, calculated from the above data, equals to 22.5±1.0 meV.     

Structural Features of Cubic Crystals Zn1 − x Me x 3d Te (Me 3d = V and Ni)

The structural state of bulk cubic Zn_{1 ? x} Me _x ^3d Te single crystals (Me ^3d are Jahn-Teller V and Ni ions with concentrations x = 0.0002 and 0.003, respectively) has been studied by thermal neutron diffraction. It has been found that the neutron diffraction patterns of the crystals contain the previously unknown scattering effects due to static deformations of the basal lattice in a wide vicinity of the 3d ions.     

Inclusive neutron and lambda production in proton-proton interactions at 12 and 24 GeV/c

A method for the determination of neutron spectra in a bubble chamber experiment is developed. Double differential cross sections for inclusive neutron and lambda production are presented. The n/Λ particle ratios are determined as functions of x and p_T; at p_T = 0 GeV/c they are compatible with the ratios measured in pCu interactions at 24 GeV/c. Our neutron spectra are compared with spectra for protons produced near the direction of the incident neutron in pn interactions at FNAL and with neutron spectra measured in pp interactions at the ISR. Exchange mechanisms are studied in the framework of single diffraction dissociation and the triple-Regge model. The scattering of virtual pions and kaons on real protons is investigated.     

The difference of crystal fields in ErAl2 and La0.9Er0.1Al2

Inelastic neutron scattering experiments have been carried out on polycrystalline ErAl₂ and on the related pseudobinary compound La_0.9Er_0.1Al₂ in the paramagnetic phase. For ErAl₂ the parameters of the cubic crystal field could uniquely be determined as x=+0.16 and W=?0.030 meV. The results on the dilute sample are different from this and are thought to be due effective charges of Er and La being not equivalent.     

Structural features of the system of cubic crystals Zn0.999Fe0.001S1 ? x Se x (x = 0, 0.2)

The structural state of cubic single crystals Zn_0.999Fe_0.001S_{1 ? x} Se _x (x = 0, 0.2) obtained by the chemical transport method has been investigated using thermal neutron diffraction for the first time. It has been found that the diffraction patterns of these crystals contain the previously unknown effects of diffuse scattering caused by local statistic atomic displacements in the metastable fcc lattice.     

Inelastic neutron-scattering study of the phonon spectrum of Bi2Sr2CaCu2O8-based Nd-containing solid solutions

A study of the phonon spectra of Bi₂Sr₂Ca_1?xNd_xCu₂O_δ solid solutions (x=0.1, 0.25, 0.75) by inelastic neutron scattering on a DIN-2PI forward-scattering spectrometer is reported. As the Nd content increases, the frequency of the Cu-O stretching vibrational modes increases (by about 70 meV), an effect caused by a change in carrier concentration in the CuO₂ sheet and not depending on the “internal pressure.” An analysis of the displacement of the peak near 11 meV (assigned to cation vibrations in the SrO sheet of the Bi₂Sr₂CaCu₂O₈ structure) suggests that a sizable part of the Nd atoms occupy Sr positions.     

Fine structure and magnetism of bulk Zn1 − x Cr x Se single-crystal cubic compounds (0 ≤ x ≤ 0.045)

The character of structural and magnetic features of the cubic lattice of bulk Zn_{1 ? x} Cr _x Se crystals (0 ≤ x ≤ 0.045) has been investigated using thermal neutron diffraction and magnetic measurements. It has been found that the diffraction scans of doped crystals contain effects of nuclear diffuse scattering caused by local static atomic displacements in the face-centered cubic (fcc) lattice. Results of magnetic measurements of doped crystals indicate the presence of weak antiferromagnetic correlations, which are a consequence of structural features of these compounds.     

Rotational excitations of NH 4 + in (NH4) x K1−x I

We propose a gaussian model for the distribution of rotational tunneling lines which constitute the experimentally observed inelastic neutron scattering spectra in the range 0 to 0.6 meV from the mixed system (NH₄) _x K_1−x I. The intensity profiles generated by this model are in remarkable agreement with the experimentally observed ones.     

金属氢化物LaNi4.5Mn0.5Hx的热中子非弹性散射谱

本文报道了用铍过滤探测器谱仪对LaNi_4.5Mn_0.5H_x在三种不同氢含量时测量的中子非弹性散射谱。结果表明,Mn原子部分置换LaNi₅中的Ni原子后,使M—H键增强,当x=6时,高能段的第二、三振动峰分别向高频方向位移了6meV和10meV。该结果与LaNi_4.5Mn_0.5H_x的平台压力(P-C-T等温线)下降的宏观热力学性能相一致。 关键词：     

Neutron diffraction studies of the diluted spinel ferrite ZnxMg0.75−xCu0.25Fe2O4

Neutron diffraction studies have been performed in the temperature range 1050 K⩾T⩾10 K on the spinel system Zn_xMg_0.75−xCu_0.25Fe₂O₄ (x=0.0, 0.25, 0.5 and 0.75) prepared in the ceramic sintering method. Cation distributions in all the four compositions have been determined from the analysis of neutron data. A perturbed ferrimagnetic order has been observed in the compositions with x values lying in the low to intermediate range, where apparently, randomly canted spins and small fluctuating clusters are superimposed on the ferrimagnetic long range order. A complete breakdown of the ferrimagnetic stability occurs at x=0.75 as indicated by the absence of magnetic long range order. A huge diffuse scattering signal appears at the low-Q region broadening the (1 1 1) diffraction line in the low temperature neutron patterns of this composition indicating the formation of large magnetic clusters. A cluster spin glass state is suggestive for this composition.     

Crystal field effects in PrAl2

We re-examine the crystal field interpretation of inelastic neutron scattering results on PrAl₂. With the crystal field parameters x = 0.75 and W = 0.315 meV and the molecular field parameter $\text{λ}\text{=}\text{145 kOe}\text{μ}\text{B}$ we can explain the crystal field effects of susceptibility, spontaneous magnetization, specific heat capacity and electrical sensitivity of PrAl₂ rather well.     

Vacancy-vacancy and vacancy-electron interactions in TiOx

Quantitative measurements have been made of the diffuse scattering from TiO_x, single crystals with both quenched specimens and specimens at high temperatures above the ordering reaction. These measurements indicate that there are strong vacancy-vacancy interactions in the fifth and sixth neighbor shell around a vacancy (J₅ and J₆). Also there is evidence for scattering due to the Fermi surface which arises from vacancy-electron interactions (J′), not phonon-electron interactions. The energies of these interactions have been measured: J₅ ? 4 meV, J₆ ? 9 meV. J′ ? 70 meV. These interactions exhibit correlation lengths of the order of 8 nm.     

Spin waves in an Invar alloy (Fe0.65Ni0.35)

The spin wave dispersion relation in an Invar alloy Fe_0.65Ni_0.35 has been measured at 4.2 K in the [111] direction by neutron inelastic scattering.Well defined magnon groups have been observed up to an energy transfer of about 80 meV. The spin wave dispersion is well described by ?ω=Dq²(1?βq²) with $\text{D=143}\text{meV}\text{A}\text{?}$ and $\text{β=0.12}\text{A}\text{?}{}^2$. The value of D is in accord with the value extrapolated from other neutron scattering results at higher contents of Ni and disagrees with spin wave resonance results.No trace of γ-iron type antiferromagnetic order could be detected at 4.2 K in this alloy by elastic neutron scattering measurements.     

Atomic and magnetic ordering in Fe3−xVxSi alloys

Alloys of composition Fe_3?xV_xSi with x = 0.25, 0.50, 0.75, 0.90 and 1.00 were studied by neutron diffraction to obtain site distributions and information on magnetic ordering. Vanadium atoms were found to substitute almost completely on the Fe site with 8Fe near neighbors, with little evidence for other types of disorder. Ferromagnetic scattering was observed for x = 0.25, 0.50 and 0.75 in an amount consistent with the observed magnetization, but the sample with x = 0.90 showed no evidence of magnetic ordering down to 4K.     

Dynamic Deformations of the Crystal Lattice of Sphalerite in the Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se(<Emphasis Type="Italic">x</Emphasis>=0.01) Compound

Local distortions of the crystal lattice of the semiconductor compound Zn_{1 − x} Co _x Se (x = 0.01) have been investigated using thermal neutron diffraction. It has been found that the diffraction patterns of the crystal contain regions of diffuse scattering in the vicinity of strong Bragg peaks at 300 K. As the temperature decreases, the intensity of diffuse scattering effects substantially decreases. Arguments in favor of the assumption that the origin of the diffuse scattering is caused by the Jahn-Teller vibronic effect are presented.