On the miscibility gap of spinels MnxFe3−xO4+γ

Annealing experiments at 940±5°C on Mn_xFe_3?xO_4+γ system were carried out in order to determine the equilibrium miscibility limits. The samples were annealed for 200 hr in sealed quartz tubes and quenched. Coexisting phases and relevant parameters were determined by X-ray diffraction. The immiscibility interval at the annealing temperature has been found by converting the $\text{c}\text{a}$ ratios to corresponding x-values to be x_cub = 2.54±0.03, x_tetr = 2.73±0.03. The experiments concerning the possible influence of the oxygen content are also reported.A corrected version of the phase diagram based on the results obtained as well as on the critically selected data published previously by other authors had been suggested and discussed on the basis of a simple model.     

The magnetic structure of U2N2Te

The magnetic structure of tetragonal U₂N₂Te has been studied by means of neutron diffraction on polycrystalline sample. A ferromagnetic alignment of the magnetic moments below 68 K has been confirmed. The best agreement between the calculated and observed intensities of the magnetic reflections has been obtained for the moment direction forming an angle 70 ± 5° to the tetragonal axis. The magnitude of the uranium ordered moment was found to be 2.50 ± 0.05 μ_B.     

Ferroelectric and optical properties of Ba6Ti2Nb8O30 single crystals

The dielectric, optical and non-linear optical properties of Ba₆Ti₂Nb₈O₃₀ single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m². The linear electrooptic constants were measured as r₃₃^T=(1·17±0·02)×10^?10 and r₁₃^T=(0·42±0·01)×10^?10 m/V. The non-linear optical coefficients were d₃₃=(15·1±2·0)×10^?12 and d₃₁=(11·0±2·0)×10^?12 m/V, which are comparable to those of Ba₄Na₂Nb₁₀O₃₀. Temperature dependences of δ₃₃ and δ₃₁ (Miller's δ) were found to be proportional to that of P_s.     

Influence of Ni-concentration on the magnetic structure in Tb(Cu,Ni)2 system

A powder sample of orthorhombic Tb(Cu_0.7Ni_0.3)₂ has been studied by neutron diffraction at T = 4.2 K and above the Curie temperature. It is found that this compound is ferromagnetically ordered at 4.2 K. The magnetic moment of Tb in this compound is (9.2 ± 0.2)μ_B, with components (2.2 ± 0.2, 0, 8.9 ± 0.1)μ_B. The influence of the Ni-concentration on the magnetic structure is discussed in the whole Tb(Cu, Ni)₂ system.     

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     

The antiferromagnetic structure of TbB4

The magnetic structure of the rare earth tetraboride TbB₄ (crystallographic space group P4/mbm) has been determined by neutron diffraction on a polycrystalline sample. Below the experimentally determined Néel temperature of T_N = (43±1) K TbB₄ is ordered antiferromagnetically. The data refinement yielded a magnetic moment value of (7.7 ± 0.2) μ_B/Tb ion at 4.2 K which we interpret as Tb⁴⁺. The magnetic structure is antiferromagnetic collinear with the moments perpendicular to the tetragonal axis.     

Neutron diffraction study of the crystal and magnetic structure of the ionic ferromagnet Cs2CrCl4

Neutron powder diffraction has been used to investigate the crystal and magnetic structure of the ionic ferromagnet Cs₂CrCl₄, T_c ～ 58K. Data taken at ambient temperature, 78 and 4.2K indicate the structure remains tetragonal $\text{I4}\text{mmm}$ at low temperatures. A ferromagnetic alignment of the spins is confirmed. The ordered moment at 4.2K is found to be 4.1 ± 0.2μ_B, and the best agreement between the calculated profile and the data suggests its direction lies at an angle of 56 ± 6° to the unique axis.     

Low temperature ESR of K2Pt(CN)4Br0.3. 3.2 H2O

Electron spin resonance has been observed in high purity single crystals of K₂Pt(CN)₄Br_0.3·3.2H₂O, (KCP), in the temperature range of 4.22–80 K. Two types of paramagnetic species are found to dominate the spectrum. One of these is an inhomogeneously broadened line showing no resolved hyperfine splitting and having g_∥ = 1.946 ± 0.003 and g⊥ = 2.340 ± 0.003. The second paramagnet is identified as a Cu²⁺ impurity center with g_∥ = 2.231 ± 0.003, g⊥ = 2.079 ± 0.002 and hyperfine tensor A_∥ = 467 MHz, A_⊥ = 70 MHz.     

The magnetic structures of HoTiO3 and ErTiO3

The magnetic structures of rare-earth titanium perovskites, ErTiO₃ and HoTiO₃, have been determined at 4.2 K by neutron diffraction. The Er³⁺ moment of (8.5 ± 0.5) μ_B lies along [001] and is colinear with the titanium moment of (-0.7 ± 0.3) μ_B. The Ho³⁺ moment of (8.1 ± 0.5) μ_B is inclined at an angle of 24° to the bc plane and 32° to the ab pla so as to produce an antiferromagnetic ordering of the x component and a ferromagnetic ordering of the y and the z components. The titanium moment of (-0.55 ± 0.3) μ_B lies in the bc plane but its precise direction has not been determined.     

Investigation of the reaction 35Cl(τ, α)34Cl at Eτ = 15 MeV

The ³⁵Cl(τ, α)³⁴C reaction has been used to study the properties of ³⁴Cl levels up to an excitation energy of 5 MeV. Angular distributions of 37 levels were measured with a split-pole magnetic spectrograph, at a bombarding energy of 15 MeV. New levels have been found at 3847, 3964, 4206, 4321 and 4715 keV, all ± 10 keV. There is a strongly excited multiplet at E_x = 5.0 MeV with components at 4939 ± 11, 4958 ± 11, 4971 ± 11, 4998 ± 12 and 5010 ± 13 keV. A DWBA analysis of the α-particle angular distributions yielded l_n values and spectroscopic factors. New spin and parity assignments were obtained. The T = 1 character of the levels at E_x = 4.21 and 4.72 MeV has been determined. Experimental spectroscopic factors are compared with results from recent many-particle shell-model calculations.     

Magnetic and structural properties of the metastable alloy Mn1.11Al0.89

Magnetic and structural properties of the metastable Mn_1.11Al_0.89 alloy have been studied by neutron and X-ray diffraction and by differential scanning calorimetry.A strong influence of the magnetic long range order on the crystalline unit cell was observed, particularly in the vicinity of 370°C.In the vicinity of the Curie temperature the structural transition of the crystalline lattice is followed by the critical exponent β_r = 0.5 ± 0.1 of the disorder parameter.     

Phase diagrams and magnetic properties of CaCu3Fe2Os2O12 quadruple perovskite: Monte Carlo study

In this paper, a Monte Carlo Simulation (MCS) has been used to study the quadruple perovskite oxide CaCu₃Fe₂Os₂O₁₂. The system has been conceived as a mixture of atoms with the magnetic moments Cu (±1/2), Fe (±5/2, ±3/2, ±1/2) and Os (±3/2, ±1/2). Phase diagrams depending on reduced exchange couplings and reduced crystal fields have been established. A stable ferromagnetic phase at the ground state has been found. Investigation of magnetic properties has been focused on the finite size analysis of magnetization and magnetic susceptibility according to reduced temperatures. Critical temperature has been calculated through simulation and the compound has been found to belong in the three-dimensional Ising model universality class.     

Optical mode softening in the incommensurate phase of Sr2Nb2O7

In the incommensurate phase below about 220°C of Sr₂Nb₂O₇, the soft mode, of which frequency decreases toward 215°C has been found by the Raman scattering measurements in the $\text{b(cc)}\text{b}$ scattering geometry. The level repulsion and the intensity transfer between the soft mode and another low frequency mode are clearly observed. The uncoupled soft mode frequency ω_s has been found to be expressed as ω_s =A(T_tr?T)^β, where β= 0.38 ± 0.02. Pressure dependence of the soft mode has also been measured up to 24kbar. No remarkable pressure dependence has been observed.     

Neutron diffraction in a random two-component magnetic system: CsMn0.96Co0.04Cl3.2D2O

Neutron diffraction expriment has been performed on the quasi-one-dimensional antiferromagnet, CsMn_0.96Co_0.04Cl₃.2D₂O, in which two different magnetic ions with competing spin anistropies are randomly distributed. Magnetic scattering data show that the easy spin axis tilts substantially (～ 40° from the easy axis of Mn salt to that of Co salt at 3.8 K) even for such a dilute mixture. The magnetic ordering temperature T_N can be definitely determined owing to the absence of the diffuse Bragg intensity at T_N, to be 4.80 ± 0.02 K. The obtained value of the critical index, β = 0.23 ± 0.02 is found to be considerably smaller in magnitude than both of those found in the Mn and Co salts. Some possible origins for the small β are discussed. The concentration dependence of T_N IS analyzed in terms of the impurity-linked chain model with $\text{|J}{}_{\mathrm{<mtext>MnCo</mtext>}}\text{|}\text{k}\text{= 14.7}\text{K}$.     

The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Neutron diffraction study of magnetic ordering in Tm0.5Eu0.5Se

A single crystal of the magnetic semiconductor Tm_0.5Eu_0.5Se was studied by means of neutron diffraction in the temperature range from 1.8 to 293 K. Long-range magnetic order is detected at temperatures below T_c = (18.5±1) K. The measured ferromagnetic moment component of (2.12±0.05) μ_B per rare-earth ion at saturation in zero external magnetic field indicates approximately antiparallel alignment of Tm moment and Eu spin (mutual angle 134°). The experimentally determined neutron magnetic form factor confirms the divalent state of both Tm and Eu in Tm_0.5Eu_0.5Se.     

Experimental study of the reaction νμ + e− → μ− + νe

The first observation of the reaction ν_μ + e^? → μ^? + ν_e has been made in the bubble chamber Gargamelle exposed to the CERN SPS wide-band neutrino beam. A signal of 26 ± 6 events has been found. This is 0.90 ± 0.20 times the prediction of the V - A theory.     

Magnetic structures of the rare earth orthotitanites RTiO3; R = Tb,Dy, Tm and Yb

The magnetic structures of the rare earth orthotitanites, RTiO₃, R = Tb, Dy, Tm and Yb, have been solved using neutron powder diffraction techniques.Two different types of magnetic structure have been found. One has the titanium and rare earth moments antiparallel along the c axis. The other structure has the rare earth moments in the ab plane with both ferromagnetic and antiferromagnetic components. In TbTiO₃, the terbium moment of (8.1 ± 0.4)μ_β has ferromagnetic and antiferromagnetic components along the [100] and [010] directions, respectively, with the moments lying at an angle of (36 ± 3)° to the [100] direction. In DyTiO₃, the dysprosium moment of (9.7 ± 0.7)μ_β has ferromagnetic and antiferromagnetic components along the [010] and [100] directions, respectively, with the moments making an angle of (31 ± 5)° to the [010] direction. TmTiO₃ has a thulium moment of (6.0 ± 0.4)μ_β in a ferromagnetic array along the [001] direction. The average titanium moment in the orthotitanites is (0.7 ± 0.3)μ_β in a direction antiparallel to the ferromagnetic component of the rare earth moment. The ytterbium moment in YbTiO₃ is quenched. It is found to be (1.7 ± 0.2)μ_β assuming a moment direction along [001]. The rare earth moment directions are found to be remarkably consistent in the series RMO₃, M = Ti, Cr, Fe and Al.     

Magneto-optical measurement on the layer type magnet (CH2)2(ND3)2MnCl4

The linear birefringence (LB) of the antiferromagnet (CH₂)₂(ND₃)₂MnCl₄ has been measured as a function of temperature and in magnetic fields up to 100 kOe. The temperature dependence of the LB points to a pronounced two dimensional magnetic behaviour. No anomaly corresponding to the effect of three dimensional ordering could be detected at T_N. In theffield dependent measurements the spin flop at H_SF = 33.6 ± 1 kOe (T = 4K) could clearly be detected.     

Measurement of the π−n→π−π−p cross section near threshold

The cross section for the reaction π^?n→π^?π^?p has been measured in a deuterium bubble chamber. The cross section at E_π,lab = 226, 250 and 312 MeV was found to be equal to 9.4 ± 2.3, 25.0 ± 5.3 and 57 ± 10 μb, respectively.