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.     

Magnetic and structural characteristics of the R3Ni7B2 compounds (R = rare earth)

Magnetic and structural behaviour and phase relationships of materials of composition R₃Ni₇B₂ (R = Nd-Lu) were investigated. Detailed X-ray analysis yields that two hexagonal structures are encountered. For the heavy rare earth (Gd-Lu) the compounds crystallize in the CeNi₃ structure. The space group is P6₃/mmc and each unit cell contains two formula units. The R₃Ni₇B₂ where R = Nd-Sm (including Yb₃Ni₇B₂) crystallize in the CeCo₄B structure. The space group is P6/mmm and each unit cell contains one formula unit. The detailed crystal structures are discussed. The magnetic measurements show that Yb₃Ni₇B₂ and Lu₃Ni₇B₂ are Pauli paramagnetic. Sm₃Ni₇B₂ is ferromagnetically ordered with a huge intrinsic magnetic hardness. The magnetization at the coercive field at low temperatures is extremely time dependent. The R₃Ni₇B₂ which crystallize in CeNi₃ structure are antiferromagnetic at low temperatures. All Mossbauer and magnetization experimental results can be explained assuming an antiferromagnetic exchange interaction in both 2(c) and 4(f) crystallographic sites and a ferromagnetic interaction between these sites.     

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.     

Study of L2,3M4,5M4,5 Auger spectra of Zn and Cu in molecular ZnCl2 and (CuCl)3 vapours

L_2,3M_4,5M_4,5 Auger electron spectra of Zn and Cu have been measured in molecular ZnCl₂ and (CuCl) ₃ vapours. The spectra have been analyzed and compared with the corresponding free-atom spectra. It is found that the main features of the spectra are atomic-like. The energies are shifted by 0.55 eV in ZnCl₂ and by 3.2 eV in (CuCl)₃ towards higher kinetic energy compared with the corresponding free-atom spectra. For the intensity ratios between the L₃ and L₂ groups, the values 2.8 and 3.7 are obtained for Zn and Cu, respectively. These intensity ratio, together with energy considerations based on free-atom Dirac—Fock calculations and observed Auger shifts, indicate that the L₂L₃M_4,5 Coster—Kronig process is energetically possible in (CuCl)₃ molecular clusters but not in ZnCl₂. The satellite structure in the spectra studied also supports this conclusion.     

Crystals and magnetic structure of RMn2Si2 (R = Pr, Nd, Y) and YMn2Ge2

Crystallographic and magnetic properties of PrMn₂Si₂, NdMn₂Si₂, YMn₂Si₂ and YMn₂Ge₂ intermetallics were studied by X-ray, neutron diffraction and magnetometric measurements. The crystal structure of all four compounds was confirmed to be body-centered tetragonal (space group I4/mmm). All were found to be antiferromagnetic with Néel points at 368, 380, 460 and 395 K respectively. Neutron diffraction results indicate that their magnetic structure consists of ferromagnetic layers composed of Mn ions piled up along the c-axis. Each layer is antiferromagnetically coupled to adjacent layer. The magnetic space group is I_p4/m′m′m′. No magnetic ordering of the R sublattice was observed at 1.8 K in the case of R = Pr and Nd.     

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.     

Ferroelastic phase transition and anomalous elastic and thermal properties of betaine borate (CH3)3NCH2COO·H3BO3

The temperature and pressure derivatives of the elastic constants of orthorhombic betaine borate, (CH₃)₃NCH₂COO·H₃BO₃, have been determined by measuring temperature and stress induced shifts of resonance frequencies of thick plates at ca. 15 MHz in the range between 140 and 300 K and 0 and 3 kbar. The elastic ‘shear’ resistance c₄₄ exhibits a value as low as 0.0492×10¹⁰Nm^-2at 293 K. With decreasing temperature c₄₄ approaches zero at ca. 142.5 K, indicating an acoustic soft mode behaviour connected with a ferroelastic phase transition. The softening of c₄₄ is described in a good approximation by c₄₄(T)_p=0 =alogT/T₀ with a=0.0663×10¹⁰Nm^-2 and T₀ = 139.5 K. Further, c₄₄ decreases with increasing pressure according to the linear relation c₄₄(p)_{T=293 K} = 0.0492?0.184×10^-4p (p in bar, c₄₄ in 10¹⁰ Nm^-2). All other elastic constants show a quite normal temperature and pressure dependence. At 293 K the transition is induced by a pressure of 2.65 kbar. The transition temperature T_c depends linearly on pressure according to T_c = 142.5+0.0568 p (pinbar, T_cinK). Passing through the transition no discontinuous change of the lattice constants is observed. The three principal coefficients of thermal expansion and the pressure derivatives of the dielectric constants exhibit discontinuities at the transition. The transition is of strongly second order.     

Solid-state shifts in the L3M4,5M4,5 Auger spectra of the elements Cu TO Se

The kinetic-energy shifts between atomic and solid-state L₃M_4,5M_4,5 Auger electron spectra of Cu, Zn, Ga, Ge, As, and Se are determined with the aid of semiempirically calculated atomic and experimental solid-state Auger energies. The shift values are calculated by applying the thermochemical model to the Auger process. Good agreement is found between the calculated and experimental values.     

Hyperfine interactions in intermetallic compounds between Gd and 3d transition metals

Measurements of hyperfine interactions at ¹⁵⁵Gd nuclei in metallic compounds between Gd and 3d transition metals and at ⁶¹Ni in GdNi compounds by Mössbauer spectroscopy are reported. The results are discussed in terms of various models proposed for the electronic structure of these compounds. The Gd isomer shifts with respect to metallic Gd are at variance with the model of a strong d electron transfer from rare earths to transition metal ions. From the observation of a linear relation between magnetic hyperfine fields at Gd and at Dy nuclei in corresponding compounds it is inferred that crystal-field induced variations of Dy moments are neglible and that the conduction electron polarization induced by 4f moments is directly related to that caused by 3d moments.     

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.     

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.     

Theory of spin-polarized Auger electron spectra in ferromagnetic materials with particular attention to L23M23M23 Auger spectrum in Fe83B17

Spin polarization of L₂₃M₂₃M₂₃ Auger electrons from ferromagnetic Fe₈₃B₁₇ is calculated with a simplified model, and compared with recent experiments. The Auger electron spectrum has two peaks, corresponding to the singlet and triplet final states of a 3p hole pair. It is shown that the spin polarizations of the singlet and triplet peaks, respectively, originate from the exchange interaction between 3d and 2p spins and that between 3d and 3p spins. Similar effects are expected to be observed commonly for L₂₃M₂₃M₂₃ Auger electrons from various ferromagnetic materials including transition elements.     

The influence of easy direction of magnetisation on 59Co NMR spectrum in R2(Co1−xMnx)17 compounds

The spin echo NMR spectra of ⁵⁹Co in R₂(Co_1-xMn_x)₁₇, (R = Y, Gd) measured at 4.2 K are reported. The large shift of resonance lines is observed, that is explained as caused by reorientation of easy axis of magnetisation from easy plane to easy direction (c axis). It is suggested to explain quantitatively the spectra, that only two of four Co sites (9d and 18f) in R₂Co₁₇ structure play a dominant role in determining of anisotropy energy and the Co atoms at the 6c sites (“dumb-bell” atoms) give no direct contribution to the anisotropy energy of the compound. The corresponding changes of local anisotropy energy and the orbital part of cobalt magnetic moment characteristic for each of cobalt structural sites are calculated and discussed.     

Relaxation of the Ne(2p1) level and populations of Ne(1s2) and Ne(1s4) in an afterglow

Radiation trapping of the transition 2p₁-1s₂ of neon has been demonstrated during laser-induced fluorescence in a pulsed microwave discharge through neon. The population of Ne(1s₂) atoms is deduced. Selective excitation is useful for the determination of lifetimes and cross sections of collisions with neutral atoms. The results may be utilized in processes for the creation of metastable atoms.     

The stability of K2[Pt(CN)4]Cl0·3·x.H2O in wet and dry atmosphere

The behavior of the one-dimensional electrical conductor K₂[Pt(CN)₄Cl_0·3·x.H₂O is studied at several temperatures in both wet and dry atmospheres using chemical analysis, X-ray diffraction and magnetic susceptibility data. It is concluded that the material is a series of hydrates with x between 2.5 and 3, and that a variation in x might influence its physical properties.     

Nuclear spin-lattice relaxation of protons in low-dimensional Ising-like system: [(CH3)3NH]CoCl3 · 2H2O

The nuclear spin-lattice relaxation times of protons in a low-dimensional Ising-like system [(CH₃)₃NH]CoCl₃ · 2H₂O were measured from 1.2 to 4.2 K in zero field and in an external magnetic field applied along the spin easy-axis. The calculation for the two-magnon Raman process was carried out with respect to a ferromagnetic layer of the bc-plane. By taking the gap energy to be 14.0 K, the best fit of the theoretical curves with the data was obtained from 1.2 K to about 2.0 K. The experimental results at high temperatures deviate seriously from the prediction of this process, which is discussed in terms of a tentative model for the nuclear relaxation process associated with magnon bound states.     

On the intensity ratio I(KL2,3L2,3)/I(KL1L1) of the auger carbon lines in series of d-metal carbides

C KVV Auger spectra have been obtained for series of nd-metal carbides (n = 3,4 and 5). The numbers of electrons participating in the C KVV Auger processes for these compounds are estimated by considering the intensity ratio I(KL_2,3L_2,3)/I(KL₁L₁). It is concluded that to explain the high intensities of the KL_2,3L_2,3 Auger lines for the d-metal carbides, it is necessary to consider the participation of conduction-band electrons (and/or interatomic transitions) in the C KVV Auger decay process.     

Analysis of the (ν1 + ν2) and (ν2 + ν3) combination bands of ozone

The fine structures of the (ν₁ + ν₂) and (ν₂ + ν₃) combination bands of ozone in the 5.7-μm region have been recorded and analyzed. The two vibrational states are coupled through Coriolis and second-order distortion terms. The interaction has been treated by the numerical diagonalization of the secular determinant for the two coupled states. With the centrifugal distortion parameters fixed to the ground state values, the following constants have been obtained: ν₁ + ν₂ = 1796.26₆, A₁₁₀ = 3.610₄, B₁₁₀ = 0.4414₅, $\text{C}{}^1{}_{110}\text{= 0.3902}{}_9$, ν₂ + ν₃ = 1726.52₆, A₀₁₁ = 3.553₇, B₀₁₁ = 0.4398₂, $\text{C}{}^1{}_{011}\text{= 0.3884}{}_4$, Y₁₃ = ?0.46₆, and X₁₃ = ?0.01₀ cm^?1. In addition, the following anharmonic constants have been obtained: x₁₂ = ?7.82₁ and x₂₃ = ?16.49₄ cm^?1. The value of the dipole moment ratio, $\text{R =}\text{〈011|μ}{}_{\mathrm{z}}\text{|0〉}\text{〈110|μ}{}_{\mathrm{x}}\text{|0〉}$, is 1.30 ± 0.10.     

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.