Mössbauer study of amorphous BaO−Fe2O3−B2O3 system

HomogeneousBaO?Fe₂O₃?B₂O₃ glasses containing maximum Fe₂O₃ content of 63 mol.% are prepared by splat cooling technique. Mössbauer study reveals that the glass mainly consists of tetrahedral network of Fe³⁺O₄. Mössbauer spectrum of the glass shows a well defined hyperfine structure at low temperatures. Magnetic ordering temperature estimated is about 130 K for the most iron-rich specimen, being much lower than that of the corresponding crystalline phases, BaO;·;Fe₂O₃ and BaO·;2Fe₂O₃. The magnetic structure is suggested to be of a short-range antiferromagnetic ordering.     

Synthesis and magnetic properties of InM2+CrS4(M2+ = Mn,Fe,Co, Ni)

The crystallographic and magnetic properties of the compounds InM²⁺CrS₄(M = Mn, Fe, Co, Ni) were studied. Three of these compounds except MnInCrS₄ were antiferromagnetic. The Néel termperature and paramagnetic Curie temperature were determined to be 20 and 82K for InFeCrS₄, 36 and 115K for InCoCrS₄ and 22 and 26K for InNiCrS₄, respectively.     

TmTO3 (T = Al, Fe, CrandV). A 169Tm Mössbauer study of magnetic and crystal field properties

¹⁶⁹Tm Mössbauer measurements are reported for the distorted perovskite compounds TmAlO₃, TmFeO₃, TmCrO₃ and TmVO₃ and have been analyzed to provide information concerning the crystal field and magnetic properties of the Tm³⁺ ion. Tm³⁺ has no magnetic moment in TmAlO₃ and low temperature saturated moments of 0.09, 0.8 and 2.1μ_B in TmFeO₃, TmCrO₃ and TmVO₃, respectively. In TmFeO₃ and TmCrO₃ the magnitudes and directions of the Tm³⁺ moments are examined in terms of previously proposed magnetic structural models. In TmVO₃, the crystal field properties are very different to those in the ferrite and chromite and a reorientation of the Tm³⁺ magnetic moments, accompanied by a sharp increase in their size, is observed near 10 to 15 K.     

Fe2+ localized excitations in the random antiferromagnet with competing spin anisotropies, Fe(1−x)CoxBr2

The Fe²⁺ localized magnetic excitations observed in the Co-rich antiferromagnetic phase of the randomly mixed system with competing Ising and XY spin anisotropies, Fe(_1?x)Co_xBr₂ have been analyzed quantitatively. The calculated frequency-field diagram reproduces well the experiments. The expectation values of the Fe²⁺ spin components in the ground state are calculated. It is shown that even in the Co-rich antiferromagnetic phase Fe²⁺ spins make an angle with the c-plane of the crystal in which Co²⁺ spins are confined.     

Microwave and sub-mmwave study of CH3SiH3 including the perturbation-allowed torsion-vibration difference band (ν12=0,ν6=3)↔(ν12=1,ν6=0)

The vibration-torsion-rotation Hamiltonian in CH₃SiH₃ has been investigated using Fourier transform microwave methods and tunable sideband far-infrared spectroscopy. Four different studies have been carried out. First, the Q-branch of the torsion-vibration difference band (ν₁₂=0,ν₆=3)↔(ν₁₂=1,ν₆=0) has been measured between 17.8 and 26.6 GHz. When three quanta of the torsional mode ν₆ are excited in the ground vibrational state (gs) for (σ=−1) torsional sublevels with K=6, these transitions become allowed through resonant Coriolis-like coupling to the lowest lying degenerate mode ν₁₂ with no quanta of ν₆ excited. Second, direct l-doubling transitions in the state (v₁₂=1, v₆=0) have been observed between 8.3 and 17.5 GHz for both torsional sublevels σ=0 and σ=±1. In the limit that the intervibrational interactions vanish, the σ-splitting between lines of the same J would be difficult to resolve, but frequency differences of more than 1 GHz due to these interactions have been determined. Third, the (J=1←0) spectrum just below 22 GHz has been re-measured with higher resolution for 0?v₆?4 in the gs and for (v₆=0) in ν₁₂. Finally, the (J=45←44) spectrum near 1 THz has been obtained for 0?v₆?2 in the gs. A global data set of 3423 frequencies has been formed by merging the present 123 measurements with the data set used recently in the simultaneous analysis of the ν₁₂ and ν₅ bands by Schroderus et al. [J. Chem Phys. 115 (2001) 1392]. By refining the (gs/ν₁₂/ν₅) Hamiltonian developed in this earlier work in which the torsional motion is grouped with the vibrational degrees of freedom, a good fit to within experimental error has been obtained by varying 45 parameters. A fit of comparable quality has also been obtained using a similar analysis in which the torsional motion is grouped with the rotational degrees of freedom. The values of the molecular constants determined in the two models are compared.     

Raman scattering spectra of B2-polariton and B2 (LO) modes in paraelectric KDP

The first observation of B₂-polariton and B₂ (LO) modes in the paraelectric phase of KDP has been made by the z(xy)z + Δy and z(xy)z? Raman scattering experiments, respectively. The B₂-polariton (θ = 0.20–0.48°) spectra has revealed both the Stokes and anti-Stokes peaks. The LO-mode which is nearly critically damped has been observed. From these results the lowest B₂ mode spectrum obtained by the y(xy)x Raman scattering has been reconfirmed to be oscillatory in nature, that is, a transverse optical phonon excitation.     

ESR and photoacoustic spectra of V2O5−MO2 (M = Se, Te, Ge) glasses

ESR spectra of V₂O₅?MO₂ (M = Ge, Se, Te) glasses are investigated in the range 298–498 K. The spectra at 298 K are characteristic of V⁴⁺ with the 3d¹ electron localized on a single ${}^{51}\text{V}\text{(I =}\text{7}\text{2}$) in the glass network. At higher temperature, the hyperfine structure progressively broadens, leading eventually to a broad, single ESR peak. These results are consistent with thermally-induced electron hopping from V⁴⁺ to V⁵⁺. Photoacoustic spectra of the glass at 298 K are characteristic of V⁴⁺ in a distorted octa environment. A correlation of ESR and PAS data suggests that covalency increased as M is charged from Ge through Te to Se.     

Magnetic properties of R4Co3 (R = Gd, Y) compounds as observed by NMR

The zero field spin echo nmr spectrum of Gd₄Co₃ taken at 4.2 K is analysed and discussed on the basis of having magnetic moments of Co atoms at different structural lattice sites. For Y₄Co₃ the spin echo nmr spectrum taken as a function of the external field is discussed and explained on the basis of the coexistence of Co atoms carrying localized magnetic moments and paramagnetic Co atoms in this compound at determined structural sites.     

The multiphoton ionization spectrum of jet-cooled pyrimidine in the 3p Rydberg and B1 (π,n) states

Resonance-enhanced multiphoton ionization (REMPI) has been applied to study the n → 3p Rydberg transition of pyrimidine (jet-cooled sample and mass resolved spectrum). Only the one component, the 3p_z(B₂), appears in the (2 + 1) REMPI and the active vibrations are ν_6a = 622, ν₁ = 946, and ν_9a = 1116 cm⁻¹. The symmetry of the state was determined by polarization measurements (linear, circular polarization). The first (π^∗,n) ³B₁ triplet state appears as a one-photon resonance in the three-photon ionization process.     

Critical parameters near the ferromagnetic-paramagnetic phase transition in La0.7A0.3(Mn1−xbx)O3 (A=Sr; B=Ti and Al; x=0.0 and 0.05) compounds

The critical parameters provide important information concerning the interaction mechanisms near the paramagnetic-to-ferromagnetic transition. In this paper, we present a thorough study for the critical behavior of La_0.7A_0.3(Mn_1−xB_x)O₃ (A=Sr; B=Ti and Al; x=0.0 and 0.05) polycrystalline samples near ferromagnetic-paramagnetic phase transition temperature by analyzing isothermal magnetization data. We have analyzed our dc-magnetization data near the transition temperature with the help of the modified Arrot plot, Kouvel-Fisher method. We have determined the critical temperature T_C and the critical parameters β, γ and δ. With the values of T_C, β and γ, we plot M×(1−T/T_C)^−β vs. H×(1−T/T_C)^−γ. All the data collapse on one of the two curves. This suggests that the data below and above T_C obey scaling, following a single equation of state. Critical parameters for x=0 and x_Ti=0.05 samples are between those predicted for a 3D-Heisenberg model and mean-field theory and for x_Al=0.05 samples the values obtained for the critical parameters are close to those predicted by the mean-field theory.     

The crystal structures of the ion conductors (NH+4)Zr2(PO4)3and (H3O+)Zr2(PO4)3

The crystal structures of (NH⁺₄)Zr₂(PO₄)₃ and (H₃O⁺)Zr₂(PO₄)₃ have been determined from neutron time-of-flight powder diffraction data obtained at 15 K. Both compounds are rhombohedral, $\text{R}\text{3}\text{c}$, with cell parameters a=8.7088(1) and c=24.2197(4) Å for the ammonium compound and a=8.7528(2), c=23.6833(11) Å for the hydronium compound. In both cases the ions are completely localized in the type I cavities and hydrogen bonded to lattice oxygens. The measured unit cell parameters are relatively large for this class of compounds but the entrance ways into the cavities are still too small to allow for unrestricted movement of the ions. Thus the low conductivity of the hydronium ion is related to this and other structural features.     

EPR and magnetic susceptibility studies of xCuO·(1−x)[2B2O3·Li2O] glasses

The results of EPR and magnetic susceptibility studies on xCuO·(1?x)? [2B₂O₃·Li₂O] glasses with $\text{0?x?30 mol \%}$, are reported. The modification of EPR spectra with the increasing of CuO content are explained supposing that these are the result of the superposition of two EPR signals, one showing the hyperfine structure typical for isolated Cu²⁺ ions and other consisting from a broad line centered at g ～ 2 typical for the clustered Cu²⁺ ions. The values of the EPR parameters prove that the coordination of isolated Cu²⁺ -complexes remains approximately the same and show that Cu²⁺ ions are situated in axially distorted octahedral vicinities. EPR measurements have shown that the Cu²⁺ ions are present mostly as the isolated species when $\text{x?5 mol \%}$. Beside the dipole-dipole coupling between Cu²⁺ ions, the magnetic measurements suggest that for x>10 mol % superexchange interactions appear, too. From Curie constant is established that in this glass system the copper ions are in Cu²⁺ and Cu⁺ valence states. Also, the amounts of the copper ions in bivalent state are determined.     

Potassium ion conduction in K2O·(5 − x)Ga2O3·xAl2O3

Potassium gallate in which gallium ions are partially substituted by aluminium, K₂O·(5 ? x)Ga₂O₃·xAl₂O₃, has been prepared by sintering a mixture of K₂CO₃, Ga₂O₃, Al₂O₃ at 1500°C. It was found from X-ray diffraction that the gallate had the beta-alumina type β phase and that solid solutions were formed on substituting Ga by Al. The potassium gallate thus obtained was revealed to be a relatively high potassium ion conductor by a.c. conductivity and ionic transport number measurements. The potassium ion conductivity decreases monotonically with the aluminium content. In order to analyze the decreasing behavior of the conductivity isotherm, the slot width was calculated from the lattice parameters and the apparent porosity was evaluated using the apparent and theoretical densities. The change of the potassium ion conductivity with the substituted amount of aluminium was explained well by the variation of the slot width.     

On the induced cobalt moments in (GdxY1−x)Co3 compounds

We report the results of magnetic measurements on (Gd_xY_1?x)Co₃ compounds with x ? 0.2, in the temperature range (4.2–1300) K. The compounds are ferrimagnetically ordered, the cobalt magnetization being anti-parallel oriented to that of gadolinium. The mean cobalt moment is dependent on composition. In the paramagnetic range the reciprocal susceptibility obeys a non-linear variation. By using a two sublattices model, the mean values of the exchange interactions inside and between sublattices are determined. The analysis of the data shows that the changes of the cobalt moments are due to the variations of the exchange fields acting on these atoms. Finally, the magnetic behaviour of cobalt atoms in these compounds is discussed.     

Magnetic measurements of (La0.8Ca0.2)MnO3+y by the Faraday method

(La_0.8Ca_0.2)MnO₃+y obtained under controlled oxygen partial pressure at 1473 K was studied by the Faraday method as a function of the oxygen deficiencies [≈?0.37 ? y ? 0.00(3)]. It was found that the oxygen deficiencies have a large effect on the magnetic structure, namely they induce a transformation from a ferromagnetic (y = 0.0) to a nearly antiferromagnetic state (y ≈ -0.2).     

Study of phase transitions in A3MO3F3 compounds (A = K,Rb, Cs; M = Mo,W)

A comparative study of phase transition in six compounds: K₃MoO₃F₃, K₃WO₃F₃, Rb₃MoO₃F₃, Rb₃WO₃F₃, Cs₃MoO₃F₃ and Cs₃WO₃F₃ was performed. All of them exhibit two transitions. One, at lower temperatures is possibly due to short range order-disorder phenomena in the anion octahedra, the second one is of a ferroelectric-paraelectric type.     

A study of the K = 3nA1 - A2 centrifugal splitting in the 3ν2 and 4ν2 states of PH3 using a difference-frequency laser system

A frequency tunable infrared source has been constructed by using the (Ar-laser) - (dyelaser) difference frequency method developed by Pine and applied to the observation of the overtone bands of PH₃ 3ν₂ ← 0 and 4ν₂ ← ν₂ in the 3.4 μm region and 4ν₂ ← 0 in the 1.6-μm region. A Stark modulation method was used to increase the sensitivity of detection. For transitions which were well modulated, the minimum detectable absorption coefficient was estimated to be ～3 × 10^?7 cm^?1 using a 3-m cell. Emphasis was placed on the observation of the A₁-A₂ splitting for K = 3n rotational levels. For the 3ν₂ state splittings were observed for K = 3, 6, and 9 because PH₃ is a very nearly spherical top in this state. The magnitude and the J dependence of the observed K = 3n splittings have been analyzed by using a normal symmetric rotor Hamiltonian and a centrifugal distortion term of the form $\text{τ}{}_{\mathrm{xxxz}}\text{[(J}{}_{\mathrm{+}}{}^3\text{+ J}{}_{\mathrm{?}}{}^3\text{)J}{}_{\mathrm{z}}\text{+ J}{}_{\mathrm{z}}\text{(J}{}_{\mathrm{+}}{}^3\text{+ J}{}_{\mathrm{?}}{}^3\text{)]}\text{4}$.     

Magnetic interactions in the layer compounds MPX3 (M = Mn,Fe, Ni; X = S,Se)

The mpx₃ phases (M = Mn, Fe, Ni; X = S, Se) with sheet structures are insulators with localized moments. They show antiferromagnetic ordering at low temperatures. From the magnetic structures determined by neutron diffraction the magnetic interactions are considered and shown to be characteristic of 2D behavior.     

Magnetic properties of R3Rh2 compounds with R=Gd, Tb,Dy, Ho and Er

Bulk magnetic measurements performed on polycrystalline samples of the tetragonal compounds R₃Rh₂ with R=Gd, Tb, Dy, Ho and Er are presented. All the compounds are ferromagnetic at low temperature. However in Tb₃Rh₂ an antiferromagnetic behaviour is observed between 14 and 24 K. In Gd₃Rh₂, where the magnetocrystalline anisotropy must be negligible, it seems that the magnetic structure is not collinear. In the other compounds the observed properties essentially result from indirect exchange interactions and crystal field effects acting on the rare earth ions which lie in low symmetry sites.     

Microwave spectrum of Trioxane in four excited degenerate vibrational states,especially in the 2ν20 (E) state and the combination state ν7 (A1) + ν20 (E)

The microwave spectra of the Trioxane molecule in the doubly excited degenerate vibrational state 2ν₂₀(E) and in the combination state ν₇(A₁) + ν₂₀(E) are reported for several J values. Molecular constants of these states have been determined. The excited states ν₂₀(E) = 1 and ν₁₉(E) = 1 previously studied by a perturbation formula have been analyzed by a direct diagonalization method of the energy matrix. Parameters which give the variation of the rotational constant B_V as a function of the quantum number v have been obtained.