The antiferromagnetic structure of ErCo2Si2 by neutron diffraction

The magnetic structure of the tetragonal ErCo₂Si₂ compound is determined by neutron diffraction on powder sample at 4.2 K. The magnetic ordering is connected with a symmetry lowering, magnetic space group P_2s$\text{1}$ (Sh⁷₂)k = 000. The structure is collinear antiferromagnetic with the erbium magnetic moments making an angle of 56.2° with the c axis. The magnetic moment value for erbium is 6.75μ_B.     

Magnetic structure of BaCaFe4O8-analysis of neutron diffraction measurements

The compound BaCaFe₄O₈ crystallizes in the trigonal space group P$\text{31}$m with one formula unit per unit cell with lattice constants $\text{a = 5.4059}\text{A}$ and $\text{c = 7.7023}\text{A}$ Neutron diffraction measurements carried out on a powder sample over the temperature range 300–900 K showed that the compound undergoes a magnetic transition to an antiferromagnetic state at a Néel temperature T_N = 680 ± 5 K. Analysis of the room temperature neutron diffraction pattern gave a magnetic unit cell that has the same periodicty as the crystallographic one. An antiferromagnetic model is proposed with the iron spin magnetic moments parallel to the c-axis of the unit cell. The magnetic moment of the Fe³⁺ ion was found to be (4.5 ± 0.1)μ_B     

Magnetic study 2D-antiferromagnets Ba2NiF6 and Ba2FeF6 by neutron diffraction and mossbauer spectroscopy

The 2D-antiferromagnetism of tetragonal Ba₂NiF₆ and Ba₂FeF6 — whose structure derives from that of K₂NiF₄ — has been studied by magnetization measurements and by powder neutron diffraction. The magnetic cell is 2a, 2$\text{a}$,$\text{c}$ and the magnetic moments (μ_Ni²⁺ = 1.9μB and μ_Fe²⁺ = 3.46μB) lie along c. This has been confirmed by Mossbauer spectroscopy for Ba₂FeF₆.     

Magnetic ordering in uranium monophosphide

The magnetic ordering in uranium monophosphide (UP) has been studied by neutron diffraction from a single crystal in a magnetic field. UP orders at T_N ? 122 ± 0.1 K with the type-I antiferromagnetic structure (+-+-), the ordering taking place in a first-order transition. At T₀ = 22.5 K the ordered magnetic moment jumps from 1.7 μ_B to 1.9 μ_B. With a magnetic field H = 25 kOe applied along the [11&#x0304;10] direction, it is found that UP has the collinear single-$\text{K}$ type-I structure above T₀ and undergoes a first-order transition to the planar double-$\text{K}$ type-I structure, accompanied by a “moment jump” due to the change in the moment direction from <001> to <110>.     

Mass and energy characteristics of the 241Pu(nth, f) fragments

Fission-fragment mass and kinetic energy distributions and their correlations have been studied for the thermal neutron induced fission of ²⁴¹Pu. The global mass distribution is smooth, apart from a small shoulder at μ_H ≈ 144 probably due to the deformed shells N ≈ 88 and N ? 60 in the heavy and the light fragment respectively. When low excitation events are selected, these structures become more pronounced. Furthermore, there is a sudden increase of 1–2 MeV in $\text{E}\text{?}\text{(μ)}$ for masses around 85 and above 155 which is probably associated with a spherical shell N = 50 in the light fragment. Finally, the prompt neutron emission curve $\text{v(m}{}^1\text{)}$ is calculated.     

Spin-wave scattering from A γ-Fe47Mn53alloy

Spin waves in the antiferromagnetic alloy γ-Fe_0.5Mn_0.5 have been studied at $\text{295° K(}\text{T}\text{T}{}_{\mathrm{N}}\text{= 0.63)}$ by the inelastic neutron scattering technique. We observed an isotropic dispersion and obtained a value for the spin-wave velocity of 255 ± 30 meV Å (3.88 ± 0.50 × 10⁶ cm/sec), which is the order of the spin-wave velocity in Cr (a typical itinerant antiferromagnet). The energy gap at q = 0 was found to be 7.0 ± 0.5 meV. These results suggest the existence of a long-range spin ordering in the conduction electrons of this alloy.     

Crystal field parameters and phase transitions in ErSb

The crystal field levels of the Er ($\text{J =}\text{15}\text{2}$) ion in a single crystal of ErSb have been measured by inelastic neutron scattering. The crystal field parameters obtained by a least squares fit to the spectra at several temperatures are: B₄ = (0·473 ± 0·005) × 10^?2°K and B₆ = (0·59 ± 0·06) × 10^?5°K, which differ considerably from the values o by interpolation from measurements on other compounds. In addition the temperature dependence of the magnetic scattering in the vicinity of the Néel temperature (T_N = 3·55°K) clearly demonstrates that the transition is second order in contrast to the first order behavior suggested by specific heat measurements. Also, any lattice distortion accompanying the magnetic ordering is less than 0.1 per cent, the resolution of the present experiment.     

Heat capacity of a five-coordinated iron(III) complex,chlorobis(N,N-dimethyldithiocarbamato) iron(III), between 0.4 and 300 k: New finding of a magnetic phase transition

The heat capacity of the title complex, Fe[S₂CN(CH₃)₂]₂Cl, has been measured between 0.4 and 300 K. A λ -type phase transition with a small shoulder arising from magnetic ordering was found at (0.609 ± 0.005) K. The character of the ordered phase has been suggested to be ferromagnetic on the basis of comparison between the methyl- and ethyl-homologues. The magnetic hyperfine structure of the Mössbauer spectra and the line broadening due to electronic relaxation effects at 1.2 K hitherto reported are concluded to result from a critical slowing-down when the magnetic transition temperature is approached from the high-temperature side. A Schottky-type anomaly arising from the zero-field splitting of a single ferric ion was observed around 2 K. The excess entropy beyond the lattice contribution at low temperatures amounts to (14.05 ±0.27) J K^?1mol^?1, which cannot be accounted for solely by the magnetic entropy of Rln 4 (= 11.53 JK^?1mol^?1) for the intermediate spin of $\text{S =}\text{3}\text{2}$. Two possibilities concerning additional conntribution have been discussed; one is a mixing of spin species of $\text{S =}\text{5}\text{2}$ and the other is a tunnel-splitting of the rotational levels of four methyl-constituents. The present study cannot give a definite conclusion as to the existence of dimeric units suggested from Mössbauer spectroscopy.     

The antiferromagnetic structures of TbCu2Ge2 and HoCu2Ge2 by neutron diffraction

The magnetic structures of TbCu₂Ge₂ and HoCu₂Ge₂ were studied by neutron diffraction. At 293 K the chemical structure is tetragonal body centered, space group I 4/mmm. The magnetic cell at 4.2 K is four times larger than the chemical one with a wave vector $\text{k =}\text{1}\text{2}\text{0}\text{1}\text{2}$. The magnetic space group is triclinic P_a$\text{1}$(Sh₂⁷) for both compounds. The moment values and directions are μ_Tb = 8.48(6) [μ_B] along [110] tetr. and μ_HO = 6.5(1)[μ_B] making an angle of 81.4(°) with c and 80(°) with a₁. The structure consists of ferromagnetic (101) layers stacked antiferromagnetically.     

Neutron scattering length of terbium structure refinement and magnetic moments of terbium iron garnet

The neutron scattering length of terbium was redetermined from powder data on terbium iron garnet (TbIG) and TbO₂ by the profile analysis technique. The mean value obtained is b (Tb) = 0.735(10) x 10^?12cm. Furthermore the positional and thermal parameters of TbIG have been refined from single crystal X-ray and neutron powder data. The results from both experiments agree well. The X-ray data from a sphere of diameter φ = 282μm were collected by MoKα radiation. The refinement was carried out including an extinction parameter which was also applied to correct for anomalous transmission. The powder data were treated by the profile analysis technique where the structural parameters and the magnetic moments were refined simultaneously. Two slightly different form factor curves were applied for Fe³⁺ in the crystallographic sites. The magnetic moments for the iron ions were found to be μ = 3.69(10)μ_B for the octahedral and 3.65(10)μ_B for the tetrahedral site at room temperature. The moment for terbium is μ = 1.15(09)μ_B and the whole magnetisation for one formula unit is 0.12(0.40)μ_B. The observed moments of Fe³⁺ are considerably reduced as compared to the free ion spin only value which was calculated from a Brillouin function for $\text{S =}\text{5}\text{2}$ to be 4.34μ_Bat 300 K.     

γ-Ray multiplicity in 239Pu fission induced by resonance neutrons: experimental evidence for the (n, γf) reaction

The fission γ-ray multiplicity measurement in the ²³⁹Pu resonances has been carried out, using the Saclay 60 MeV electron linac as a neutron source. Large fluctuations are observed from resonance to resonance, in correlation with the number $\text{}\text{?}$Gn of prompt neutrons, the total energy of these γ-rays and the fission width Γ_f. The results are interpreted in terms of a competition between the fission and the radiative capture during the de-excitation of the compound nucleus. They are the first experimental evidence of the (n, γf) reaction. Some parameters like the width $\text{Г}{}_{\mathrm{\gamma f}}$ are deduced.     

Experimental study of some important characteristics of the thermal neutron induced fission of 237Np

Fission fragment mass and kinetic energy distributions and their correlations have been studied for the thermal neutron induced fission of ²³⁷Np. The global mass distribution is rather smooth, apart from a weak shoulder at μ_H = 140–141. When low excitation events are selected, fine structures associated with the charge of the fragments are observed. Furthermore, there is a sudden increase in E_k for μ_H > 155, which is probably due to a spherical shell N = 50 in the light fragment and the corresponding deformed (but stable) heavy fragments with masses in the rare earth region. For the average (pre-neutron emission) total fragment kinetic energy, a value of 176.4 ± 0.6 MeV has been obtained, in agreement with the systematics.Also the prompt neutron emission curve $\text{v(m}{}^1\text{)}$ has been calculated, which shows the well-known saw-tooth shape. Finally, the energy distribution and the emission probability of the ternary α-particles have been determined.     

Some structural and magnetic properties of 239PuD2.25 by neutron diffraction

A neutron powder diffraction study of ²³⁹PuD_2.25 compound was performed at different temperatures, in order to determine the deuterium atoms positions and to study the occurrence of structural and magnetic phase transitions. Vacancies of tetrahedral sites were found together with partial occupancy of octahedral special positions. No order disorder transitions were observed at low temperature. Below T = 60 K PuD_2.25 becomes ferromagnetically ordered with an ordered magnetic moment μ_ord = 0.8 μ_B per Pu atom.     

Magnetic properties,magnetic structure of GdMg and TbMg compounds

We have investigated the magnetic properties of GdMg and TbMg, as well as the magnetic structure of TbMg by neutron diffraction. Both compounds have a non-colinear magnetic structure with a ferromagnetic component. In GdMg, the spontaneous magnetization reaches 4.5μ_B at 4.2 K and decreases as T². For TbMg at 4.2 K, the ferromagnetic component and the antiferromagnetic component perpendicular to the propagation vector ($\text{1}\text{2}$ 0 0) are nearly equal to 5.17μ_B.     

Accurate determination of the 17O16O + n coupling constant and spectroscopic factor

We have measured ¹⁶O¹⁷O elastic cross sections at 22 MeV between 65°–140° to ± 1 %. The observed oscillatory interference between Coulomb scattering and the neutron transfer process is analyzed using exact finite-range DWBA. A model-independent value of $\text{C}\text{?}{}^2\text{= 0.82 ± 0.07}$ is obtained for the coupling constant of the 1d_{$\text{5}\text{2}$} neutron in ¹⁷O. We also present an analysis of data on magnetic electron scattering from ¹⁷O, which yields precise information on the magnitude and the radial shape of the $\text{1}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ neutron bound-state wave function. With this we relate the coupling constant to the spectroscopic factor and find S = 1.04 ± 0.11. We show that the magnetic electron scattering data alone yield S = 1.04 ± 0.10. Combining these results with earlier work we recommend $\text{C}\text{?}{}^2\text{= 0.79 ± 0.04}$ and S = 1.03 ± 0.07 as best values. This spectroscopic strength corresponds to (91 ± 7) % of the full single-particle value.     

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.     

Yield ratio for the two 241Pu fission isomers in the 242(γ, n) reaction

The half-lives and yield ratios for the two ²⁴¹Pu fission isomers have been measured in the ²⁴²Pu(γ, n) reaction. The observed half-life for the long-lived isomer $\text{(T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 20.5 ± 2.2 μs)}$ is in agreement with previous data, and the existence of a short-lived 34 ± 7 ns isomer in ²⁴¹Pu could be confirmed. The measured yield ratios are Y_iso/Y_pr = (9.2 ± 0.8) × 10^?5 and Y_iso/Y_pr = (3.7 ± 0.7) × 10^?5, respectively. From a statistical model analysis of the isomeric fission yield ratio, Y^long_iso/Y^short_iso = 2.5 ± 0.6, a spin assignment for the two isomers is attempted. Possible spin combinations are compared with single-particle shell-model calculations and with available spectroscopic data for the other even-odd Pu isotopes.     

The g-factor of the 132+ state in 207Po and the mesonic contribution to the moment of the i132-neutron

The magnetic moment of the $\text{13}\text{2}{}^{\mathrm{+}}$ state in ²⁰⁷Po was determined to be μ = ?0.910 ± 0.014 n.m. An analysis of this value and other known moments of $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron states around ²⁰⁸Pb supports the existence of a mesonic contribution of at least ?0.3 n.m. to the moment.     

The critical behaviour of spontaneous magnetization in the antiferromagnetic NiO

The spontaneous magnetization of the sublattice vs temperature in the antiferromagnetic NiO was measured by the neutron diffraction method. Temperature changes of the Bragg peaks (111), (222), (333) and (444) with the wavelengths of neutrons $\text{λ}{}_{\mathrm{I}}\text{= 4.16}\text{A}\text{?}$, $\text{λ}{}_{\mathrm{II}}\text{= 2.08}\text{A}\text{?}$, $\text{λ}{}_{\mathrm{III}}\text{= 1.39}\text{A}\text{?}$ and $\text{λ}{}_{\mathrm{IV}}\text{= 1.04}\text{A}\text{?}$, respectively were simultaneously investigated by the neutron time-of-flight spectrometer. On the basis of these measurements, the transition temperature from the antiferromagnetic into the paramagnetic phase was determined, T_N = (523 ± 1)°K. The temperature function of the (111) magnetic peak intensity has been accepted to be I ～ (T_N?T)^2β. According to the present measurements the critical point exponent is 0.33 ± ^0.02_0.04.