Optical investigation of DyFeO3

Optical absorption spectra of DyFeO₃ have been investigated at 1.2≦T≦4.2 °K, andT=77 °K From the temperature dependent lineshift a Néel temperature ofT _N=(3.8±0.5) °K is deduced for the dysprosium sublattices. The groundstate splitting due to the iron-dysprosium interactions is about 1.5 cm^?1 and due to the dysprosiumdysprosium interactions (5.0±1.4) cm^?1. Zeeman studies give the magnetic moment of the dysprosium ions asμ=(9.2±1.0)μ _B.     

Hall effect and magnetoresistance of (SN)x films

Hall effect and electrical conductivity have been investigated between 77 K and 300 K and the magnetoresistance at 4.2 K for a number of (SN)_x films deposited at substrate temperatures between — 10 and 50°C. The small magnitude of the Hall mobility (? 1 cm² Vsec^?1 at 300 K) and its activated temperature dependence are interpreted in terms of a heterogenous model for (SN)_x films with thin depletion layers separating highly conductive islands. The hole concentration in these islands (p ≈ 10²¹ cm^?3, the microscopic mobility (μ ≈ 500 cm² Vsec^?1 at 4.2 K) and the temperatures dependence of μ are found to be close to values for (SN)_x crystals.     

Optical investigation of HoFeO3

The absorption spectra of HoFeO₃ were investigated in the near infrared spectral region at temperatures of 1.2, 4.2, 20 and 77 °K respectively. At every temperatureT≦20 °K all the absorption lines show the same splitting which is attributed to the groundstate; this splitting is (7.2±0.5) cm^?1 at 20 °K and decreases to (4.9±0.8) cm^?1 extrapolated to 0 °K. From these splittings the holmium-iron and the holmiumholmium interactions can be deduced. Measurements with an external magnetic field yield a magnetic moment ofμ=(7.6±0.7)μ _B per holmium ion. The moments are directed at angles of ?28° and ?152° with respect to theb-axis.     

Electron paramagnetic resonance in deuterated nickel fluosilicate

Electron paramagnetic resonance measurements in single crystals of NiSiF₆. 6D₂O were made at K, Ku and Ka bands at 4.2 K and between 77 K and 300 K. The measured g values were in the range 2.23–2.26, while the zero-field splitting parameter D varied from ?(0.185 ± 0.005) cm^?1 at 4.2 K to ?(0.53 ± 0.01) cm^?1 at 298 K. The parameters of the trimolecular hexagonal unit cell were determined to be approximately a = 9.28 Å, c = 9.58 Å from powder X-ray diffraction measurements at room temperature.     

Optical investigation of ErFeO3

The absorption spectrum of single crystals of ErFeO₃ has been investigated in the red and near infrared spectral region in the temperature range between 1.2 °K and 4.2 °K and at 20 °K and 77 °K. Between 77 °K and 4.2 °K a constant splitting of the absorption lines is observed. Below the Néel-temperature of the erbium sublattice at 4.5 °K the splitting of the absorption lines increases; the saturation value extrapolated to 0 °K of the splitting of the lowest crystal field level of the⁴ I _15/2 groundterm is (6.08±0.30) cm^?1. By measuring the Zeeman effect the groundstate magnetic moment is determined asμ=(6.6±0.2)μ _B. The measured temperature dependence of the splitting of the lowest crystalfield level of the⁴I_15/2 groundterm is compared with that calculated by a Monte Carlo method.     

Z-dependence of the intensity of |Δn|=2 pionic X-rays

The intensity per stopped π^?of|Δn|=2 pionic X-rays are observed to have larger variations with atomic number Z than do the |Δn|=1. The 6–4 intensity has a well-defined maximum at Z=34 with a FWHM of ΔZ ～10.     

Absorption spectrum of Cr3+ ion doped in lithium ammonium sulphate single crystal

The absorption spectrum of Cr³⁺ ion doped in lithium ammonium sulphate single crystal has been studied both at room (300 K) and liquid nitrogen (77 K) temperatures. From the nature and position of the observed bands, O_h symmetry is assumed for the ion. The spectroscopic parameters derived for the ion in the crystal at 77 K are Dq = 1655 cm^?1, B = 735 cm^?1 and C/B = 4.4     

EPR and optical absorption studies of Cr ions in potassium sodium dl-tartrate tetrahydrate

EPR spectra of Cr³⁺ ions doped in potassium sodium dl-tartrate tetrahydrate single crystals are recorded at 77 K. The spin Hamiltonian and zero field parameters g, |D| and |E| are measured from the resonance lines obtained at various rotations of the magnetic field. The values obtained are: g_x=1.9257±0.0002, g_y=1.9720±0.0002, g_z=2.0102±0.0002, |D|=313±2 (×10⁻⁴) cm⁻¹ and |E|=101±2 (×10⁻⁴) cm⁻¹. From the results of EPR study, the site symmetry of Cr³⁺ ion in the crystal is discussed. The optical absorption at room temperature is also studied. From the observed band positions, the crystal field splitting parameter (D_q) and the Racah inter-electronic repulsion parameters (B and C) are evaluated. The bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed.     

Non-cubic Mn2+-centers in BaF2

The EPR spectra of thermally treated BaF₂: Mn samples is reported. After thermal annealing at 900 K a trigonal Mn²⁺ center with g=2.000±0.005, |D|=2725±40MHz, |A|=265±10MHz, $\text{D}\text{A}\text{>0}$, is observed. Annealing at 1200 K produces an orthorhombic Mn²⁺ center with g=2.00±0.01, |D|=2430±40MHz, |E|=570±20MHz, |A|=265±10MHz, $\text{D}\text{A}\text{<0}$. The superhyperfine (SHF) structures due to interactions with the neighbouring fluorines indicates that the trigonal manganese interacts with four fluorines, three of them equivalent. The orthorhombic Mn²⁺ shows interaction with four equivalent fluorine nuclei.     

New type of photoconduction in n-CdS2

Four strong resonances have been observed in the far-infrared transverse magnetophotoconductivity of n-CdS at 1.2 and 4.2 K. The resonances are observed in the spectral range 10–120cm^?1 at fields to 90 kOe. Two of these resonances are inconsistent with previously observed photoconductive mechanisms; a new mechanism which explains the observed resonances is proposed.     

Electrical conductivity of urea nitrate single crystal

The electrical conduction in urea nitrate single crystal has been found to be anisotropic. The conductivities measured in the directions parallel and perpendicular to the cleavage plane were 1.5 x 10^?8 and 1.2 x 10^?11 ohm^?1 cm^?1 at 300 K, respectively.     

Supertransferred hyperfine structure in EPR of V4+ ion in Ca3In2Ge3O12 garnet

Interaction of an unpaired electron of the tetrahedral V⁴⁺ ion in Ca₃In₂Ge₃O₁₂ garnet with the four nearest In nuclei gives rise to clearly resolved structure of EPR spectra. We report the observation and analysis of these spectra at three frequencies and at temperature 77 K. The temperature dependence between liquid helium and the room temperatures was also studied. Parameters of the spin Hamiltonian are g_∥=1·8735; g_⊥=1·9825; ∣ ¦A∥|=150·4×10^?4cm^?1; ¦ A_⊥¦ = 36·7 × 10^?4 cm^?1. The supertransferred hyperfine interaction was found to be isotropic, absolute value of the corresponding parameter a is 22·1 × 10^?4 cm^?1.     

Brillouin scattering observation of phonon renormalization in KC1:CN−

The phonon-defect interaction in KC1:CN^? has been studied in the 16 GHz frequency range using the Brillouin scattering technique. Brillouin spectra of KC1:CN^? at 4.2 K show a defect induced phonon velocity renormalization. The measurements are consistent with a 〈111〉 oriented CN^? dipole in KC1 with a tunneling level of T_2g symmetry at 2.6 cm^?1 and a coupling constant of 1.5 × 10^?21 cm³.     

231Pa Mössbauer resonance in Pa metal

The Mössbauer resonance of the 84.2 keV transition in ²³¹Pa has been measured for an absorber of Pa metal at 4.2 K with respect to a source of ThO₂ at 4.2 and 65 K. The resulting nuclear parameters are compared with calculations based on the Nilsson model. The electric field gradient in Pa metal is |eq_z| = (2.05 ± 0.15)} 10¹⁸ V/cm².     

Charmonium sum rules andη c production in two-photon reactions

The coupling of the pseudoscalar charmonium stateη _c to two photons is calculated using the charmonium sum rules. The resulting value of the two-photon decay width is Λ=5.6 KeV (±10%). If the virtualness of one of the photons is increased from |k ₁ ² |=0 to |k ₁ ² |=1 GeV² the coupling decreases about 10%.     

Absorption spectrum of Cs2Mg(SO4)2 · 6H2O:Ni2+ single crystals

The absorption spectrum of Ni²⁺ doped in Cs₂Mg(SO₄)₂ · 6H₂O single crystals has been studied at room and liquid nitrogen temperatures in the range 7000–34000 cm^?1. The observed spectrum is satisfactorily interpreted in terms of cubic ligand field model including spin-orbit coulping. The ligand field parameters evaluated to best fit the observed spectrum are B = 955 cm^?1, C = 3572 cm^?1, Dq = 910 cm^?1 and ξ = 550 cm^?1. The non-ligand field band observed at 77K has been interpreted to be the superposition of vabrational mode of SO₄^2? radical on ₃T_1g(F) band.     

Absorption spectra of diatomic molybdenum nitride (MoN), molybdenum oxide (MoO), and molybdenum dimer (Mo2) molecules isolated in Ar,Ne, and Kr matrices

MoN and MoO molecules produced in a hollow cathode discharge have been trapped in Ne, Ar, and Kr matrices at 4.2 and 13 K and investigated by optical spectroscopy. Bands attributed to MoN were identified in the red and blue spectral regions and assigned by comparison with gas phase results to the A⁴π → X⁴Σ^? (a) and B⁴Σ → X⁴Σ^? (a) transitions, respectively. The ground state of Mo¹⁴N has been identified as ⁴Σ^? with ω_e = 1040 cm^?1 in an Ar matrix. Absorptions assigned to MoO in the red spectral region form the (0-0) and (1-0) bands of at least one electronic transition, but could not definitely be correlated with the gas phase results. The ground state vibrational frequency for Mo¹⁶O in an Ar matrix is 893.5 cm^?1. Additionally, Mo₂ absorptions centered at 19 305 cm^?1 were shown to be part of a vibrational progression with an average spacing of 181 cm^?1.     

Tunable diode laser measurements of N2- and air-broadened halfwidths: Lines in the (ν4 + ν5)0 band of 12C2H2 near 7.4 μm

Nitrogen- and air-broadened Lorentz halfwidths have been determined for 29 lines in the P and R branches of the (ν₄ + ν₅)⁰ combination band of ¹²C₂H₂ using a tunable diode laser spectrometer. Two tunable diode lasers operating in the region 1250–1380 cm^?1 were used in recording the data. For nitrogen broadening, the measured halfwidths at 296 K decrease from about 0.11 cm^?1 atm^?1 at |m| = 1 to about 0.05 cm^?1 atm^?1 at |m| = 30, where m = J″ + 1 for R-branch lines, m = ?J″ for P-branch lines, and J″ is the lower state rotational quantum number. On the average, the air-broadened halfwidths are 97% of the N₂-broadened halfwidths.     

Evaluation of exchange interaction in binuclear copper(II) chelates of amide-based cyclophanes

Temperature dependence of the electron paramagnetic resonance (EPR) spectra of binuclear Cu(II) complexes with amide-based cyclophanes, Cu₂(bis-EDTAPDN), Cu₂(bis-EDTANAP) and Cu₂(bis-EDTABPE), in 60% methanol (pH ca. 10) has been studied at a frequency of 9.43 GHz in the temperature range of 77–4.2 K; the cyclophanes are macrocyclic compounds in which four amide bonds link two ethylenediaminetetraacetate (EDTA) units and two units of the aromatic diamine 1,4-phenylenediamine (DPN), 1,5-diaminonaphthalene (NAP) or bis(4-aminophenyl) ether (BPE). Exchange integrals found from the EPR measurements are ca. 70–105 cm^?1, 22 cm^?1 andJ ≤ 0, for Cu₂(bis-EDTAPDN), Cu₂(bis-EDTANAP) and Cu₂(bis-EDTABPE), respectively; the sign ofJ is defined to be positive for antiferromagnetic interaction. The variation of exchange interactions in these compounds is related to the nature of the bridging organic groups.     

Time decay of optically injected free carriers in highly excited GaAs

The time decay of large densities of optically injected free carriers in epitaxial GaAs has been obtained from time-resolved mm wave reflectivity at 300°K. The decay time increases from 5 to 200 nsec as the epitaxial layer thickness increases from 1 to 72 μm, but is independent of injection level (Δn ～ 10¹⁶to 10¹⁸cm_?3) and doping level (norp ～ 10¹⁴to 10¹⁶cm^?3).