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.     

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.     

Optical investigation of dysprosiumaluminumgarnet (DyAlG)

The absorption spectrum of the transitions⁶ H _15/2→⁶ F _3/2,⁶ F _5/2 in Dysprosiumaluminumgarnet (DyAlG) is investigated. In the antiferromagnetic state (T _N =2,49°K) a splitting of the crystal field levels by an internal magnetic field is observed. The splitting of the lowest crystal field level I of the groundterm in the internal field is (5,2±0,5) cm^?1, extrapolated to 0°K.     

Electron paramagnetic resonance of Dy3+ in cubic ZnSe and Tm3+ in hexagonal CdS single crystals

Electron paramagnetic resonance has been observed for Dy³⁺ in ZnSe and Tm³⁺ in CdS. For Dy³⁺ doped ZnSe, an isotropic spectrum was observed having well resolved hyperfine lines due to ¹⁶¹Dy and ¹⁶³Dy. The g value obtained was 6.577 ± 0.002 and ¹⁶¹A was 191 ± 1 × 10⁴ cm^?1 and ¹⁶³A was 265 ± 3 × 10^?4 cm^?1. The agreement of the observed g value to g(τ₆) = 6.667 and the point-charge calculations suggest that Dy³⁺ occupies an interstitial (II) site with no local charge compensation. For Tm³⁺ doped in hexagonal CdS, an axial spectrum consistent with g_⊥ = 0, g_∥ = 10.722 ± 0.007, D = 2.57 GHz (crystal field splitting) and ¹⁶⁹A = 1207 ± 5 × 10^?4cm^?1. The large g_∥ value indicates that the Tm ion exits in the trivalent state. This is in reasonable agreement with previous reports of the non-Kramer's state of Tm³⁺.     

Optical spectroscopy of Dysprosium Aluminum Garnet (DAG)

The absorption spectrum of antiferromagnetic dysprosium aluminium garnet (DAG) (T _N =2.50 °K) has been investigated at low temperatures. The groundstate splitting due to all interactions in the antiferromagnetic state is (5.27±0.10) cm^?1 extrapolated to 0 °K. The temperature dependence of the lineshift of the absorption lines is measured. Zeeman effect studies give theg-tensor of the groundstate asg _z =18.4±0.5,g _x =g _y =0.5±0.2. The studies also allow the determination of the critical fields asH _c ^[100] =(5.0±0.1) koe,H _c ^[111] =(3.9±0.2) koe andH _c ^[110] =(4.9±0.6) koe. In addition an investigation of a number of satellite lines is performed. Some of them can be interpreted as spin wave sidebands (Stokes and anti-Stokes); others obviously come from dysprosium ions which have impurity ions on regular lattice sites as neighbours.     

EPR, Optical Absorption and Superposition Model Study of Fe3+-Doped Ammonium Dihydrogen Phosphate Single Crystals

X-band electron paramagnetic resonance (EPR) studies are carried out on Fe³⁺ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe³⁺ ion in ADP are: g = 1.994 ± 0.002, |D| = (220 ± 5) × 10^?4 cm^?1 and a = (640 ± 5) × 10^?4 cm^?1. On the basis of EPR data, the site symmetry of the Fe³⁺ ion in the crystal is discussed. The Fe³⁺ ion enters the lattice substitutionally replacing the NH₄ ⁺ sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195–925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the ⁶ A _1g (S) ground state to various excited quartet levels of the Fe³⁺ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D _q ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D _q  = 1,380 cm^?1 and α = 90 cm^?1, respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B _kq parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 ± 5) × 10^?4 cm^?1 and |E| = (21 ± 5) × 10^?4 cm^?1.     

EPR and Optical Absorption Study of Cr3+-Doped Dipotassium Tetrachloropalladate

X-band electron paramagnetic resonance (EPR) study of Cr³⁺-doped dipotassium tetrachloropalladate single crystal is done at liquid nitrogen temperature. EPR spectrum shows two sites. The spin-Hamiltonian parameters have been evaluated by employing hyperfine resonance lines observed in EPR spectra for different orientations of crystal in externally applied magnetic field. The values of spin-Hamiltonian and zero-field splitting (ZFS) parameters of Cr³⁺ ion-doped DTP for site I are: g _x  = 2.096 ± 0.002, g _y  = 2.167 ± 0.002, g _z  = 2.220 ± 0.002, D = (89 ± 2) × 10^?4 cm^?1, E = (16 ± 2) × 10^?4 cm^?1. EPR study indicates that Cr³⁺ ion enters the host lattice substitutionally replacing K⁺ ion and local site symmetry reduces to orthorhombic. Optical absorption spectra are recorded at room temperature. From the optical absorption study, the Racah parameters (B = 521 cm^?1, C = 2,861 cm^?1), cubic crystal field splitting parameter (Dq = 1,851 cm^?1) and nephelauxetic parameters (h = 2.06, k = 0.21) are determined. These parameters together with EPR data are used to discuss the nature of bonding in the crystal.     

Optical investigation of metamagnetic DyAlO3

We have investigated the optical absorption spectra of metamagnetic DyAlO₃ (T _N =3.4 °K) above and below the Néel temperature. We find that the magnetic interactions are predominantly between the ions along the crystallographicc-axis; the interaction energy between two ions isW _C =? (2.9±0.6) cm^?1. Additional line-shifts below 3.4 °K yield the Néel temperature. Zeeman effect studies give the magnetic moment of the groundstate as μ=(9.2 ± 0.9)μ _B . The direction of the magnetic moments is in thea-b plane, with angles of ± 33.5° and ± 146.5° from theb-axis. The Zeeman effect studies reveal two metamagnetic transitions (forH _ext∥μ) at 7.0 and 7.3 kOe respectively. Additional susceptibility and Mössbauer measurements confirm the Néel temperature and the magnetic moment.     

Diffusion constant and surface states of positrons in metals

Positron lifetime spectra and angular correlation curves for seven fine-grained powders of Fe, Co, Ni, and W are analyzed. From the lifetime data, the positron diffusion constant in metals atT=300°K was found to beD ₊=(1.0±0.5)×10^?2 cm² sec^?1. Evidence is presented that positrons are trapped in metal surface states.     

Negative Ions,Ozone, and Metastable Components in dc Oxygen Glow Discharge

In a dc glow discharge in oxygen, the concentrations of minor components of O₂(a¹Δ_g), O₂(b¹ Σ_g), O₃, O(¹D), as well as nagative ions and electrons have been measured. Balance equations have been derived which describe satisfactorily the stationary concentrations of these components as functions of gas pressure and discharge current. For the first time, the rate constants of important aeronomical reactions (a) O^? + O₂(a¹Δ_g) → O₃ + e, (b) O₂^? + O₂(a¹Δ_g) → 2O₂ + e and (c) e + O₃ → O₂^? +O have been measured as functions of gas temperature T and mean energies of ions E_i and electron E₆: K_a = (2.5 ± 0.5) · 10^?9 · (T/300)^{4 ± 0.4}· (E_i/0.04)^{?2.6 ± 0.4} cm³/s for T = 385?605 K and E_i = 0.10 ? 0.66 eV; K_b = (1.0 ± 0.3) · 10^?10 · (T/300)^{?2 ± 0.5} · (E_i/0.04)^{0.23 ± 0.05} cm³/s for T = 330?605 K and E_i = 0.09 + 1.5 eV; K_c for E_e = 0.8÷5 eV.     

Study of crystal-field excitations and Raman active phonons in o-DyMnO3

In DyMnO₃ orthorhombic single crystals, the weak Raman active phonon softening below T=100 K is correlated with the study of infrared active Dy³⁺ CF excitations as a function of temperature and under applied magnetic field. We detect five H_13/2 CF transitions that we predict with appropriate CF Hamiltonian and we confirm that the magnetic easy axis lies in the ab plane. While the CF energy level shifts below T=100 K reflect different displacements of the oxygen ions that contribute to the phonon softening, lifting of the ground state Kramers doublet degeneracy (∼30 cm⁻¹) is observed below T_N=39 K due to the anisotropic Mn³⁺−Dy³⁺ interaction, which could be responsible for the stability of the bc-cycloid ferroelectric phase.     

Optical absorption spectrum of Ni2+ ion doped in synthetic lecontite

The optical absorption spectrum of Ni²⁺ ion doped in lecontite (sodium ammonium sulphate dihydrate) single crystal has been studied at room and liquid air temperatures. All the bands could be assigned assumingO _h symmetry for the Ni²⁺ ion in the crystal. The splitting of³ T _1g (F) band at liquid air temperature has been attributed to spin-orbit interaction. The crystal field and spin-orbit parameters derived areD _q=1000 cm^?1;B=740 cm^?1;C/B=4.27 and ζ=600 cm^?1. All the bands observed show a blue shift when the crystal was cooled to liquid air temperature.     

Zeitliches Abklingen und Anisotropie von p-Terphenyl- undp-Terphenyl-Anthrazen-Mischkristallen bei Beschuß mit α-Teilchen

The time dependence of scintillation intensity from single crystals ofp-terphenyl and mixed crystals ofp-terphenyl and anthracene after bombarding with α-particles was investigated at the two temperaturesT=296 °K andT=92 °K. For the crystals ofp-terphenyl the time dependence of the scintillation anisotropy was also measured. Using the formulas given byKing andVoltz the decay curves ofp-terphenyl were decomposed into two components. Good agreement between experiment and theory was found. The ratio of the prompt intensity to the delayed intensity was determined to be 1∶2 atT=296 °K and 1∶3 atT=92 °K. The diffusion constants for triplet excitons were calculated to beD _T(296 °K)≈10^?5 cm² sec^?1 andD _T(92 °K)≈ 2×10^?6 cm² sec^?1, and the triplet-triplet interaction rate constantsχ _tt(296 °K)≈ 2.5×10^?11 cm³ sec^?1 andχ _tt(92 °K)≈0.5×10^?11 cm³ sec^?1.     

Temperature dependence of Mn2+ EPR in Sn2P2S6 near the phase transition

The X-band EPR spectrum of Mn²⁺ in Sn₂P₂S₆ was studied in the temperature rangeT=223–363 K. At room temperature the spin-Hamiltonian constants areg=2.00±0.01,B ₂ ⁰ =(163±3)·10^?4 cm^?1,B ₂ ² =(159±3)·10^?4 cm^?1,A=?(75±1)·10^?4 cm^?1. The effect of the invariance in temperature of the resonance magnetic fields in the narrow temperature rangeT=337–340 K and the model of the paramagnetic centre are discussed. According to EPR data a phase transition occurs atT=337 K. This transition from the paraelectric phase to the ferroelectric one is accompanied by a dramatic change in value of the spin-Hamiltonian constantB ₂ ⁰ .     

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.     

Effect of 100 MeV swift Si8+ ions on structural and thermoluminescence properties of Y2O3:Dy3+nanophosphor

Nanoparticles of Y₂O₃:Dy³⁺ were prepared by the solution combustion method. The X-ray diffraction pattern of the 900°C annealed sample shows a cubic structure and the average crystallite size was found to be 31.49?nm. The field emission scanning electron microscopy image of the 900°C annealed sample shows well-separated spherical shape particles and the average particle size is found to be in a range 40?nm. Pellets of Y₂O₃:Dy³⁺ were irradiated with 100?MeV swift Si⁸⁺ ions for the fluence range of 3?×?10^11_3?×?10¹³ ions cm^?2. Pristine Y₂O₃:Dy³⁺ shows seven Raman modes with peaks at 129, 160, 330, 376, 434, 467 and 590?cm^?1. The intensity of these modes decreases with an increase in ion fluence. A well-resolved thermoluminescence glow with peaks at ～414?K (T_m1) and ～614?K (T_m2) were observed in Si⁸⁺ ion-irradiated samples. It is found that glow peak intensity at 414?K increases with an increase in the dopant concentration up to 0.6?mol% and then decreases with an increase in dopant concentration. The high-temperature glow peak (614?K) intensity linearly increases with an increase in ion fluence. The broad TL glow curves were deconvoluted using the glow curve deconvoluted method and kinetic parameters were calculated using the general order kinetic equation.     

Disordering effects and property changes in fast neutron irradiated YIG

Damage region structure and property changes of YIG irradiated atD=10¹⁸?7.8×10¹⁹ n/cm² were studied. Damage regions at 300 K were found to consist of 1) a core of Fe³⁺ paramagnetic phase (PP) withgΔ=0.8 mm/s; 2) a shell of Fe³⁺ intermediate magnetic phase with heavily distorted bond geometry and <H _eff>≤300 kOe; 3) Fe³⁺ (a, d) surrounded by oxygen vacancies and interstitials. The dose dependence of PP concentration is given byC _PP=1-exp(?βD), yielding PP core radiusr _PP=12,5 Å. Magnetic ordering in PP was found to arise atT _tr=90 K. NGR probabilityf′ under irradiation was found to decrease linearly according to Δf′/f′=?C _PP(D). Net magnetization change was found, using the Gilleo model, to obey an analogous relationship ΔM(T)/M(T)=?C _PP(D).T _c dose dependence is given by ΔT _c/T _c=?0.5×C _PP(D) and can be related to lattice parameter change to yield Δa ₀/a ₀=(1.42±0.04)×10^?4×C _PP(D). External field experiments revealed a complex dependence ofK ₁ on PP concentration, elastic stress field magnitude and a with a minimum atD=10¹⁹ n/cm².     

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.     

EPR study of the ferroelectric phase transition in chromium-doped DMAAS

X-band electron paramagnetic resonance (EPR) investigations of single crystals of Cr³⁺-doped dimethylammonium aluminium sulphate hexahydrate are presented from 100 K to room temperature. The crystal undergoes a phase transition at 152 K from the ferroelastic to the ferroelectric phase. The spin-Hamiltonian parameters have been determined for both phases. The spin-Hamiltonian parameters in the ferroelectric phase are:g=1.980±0.003,b ₂ ⁰ =(1140±15)·10^?4 cm^?1,b ₂ ² =(214±10)·10^?4 cm^?1. Remarkable EPR line width changes confirm the order-disorder character of the ferroelectric phase transition on a microscopic level and demonstrate that the dimethylammonium reorientation freezing-out is the prime reason for this transition.     

ESR study of Fe3+ and Mn2+ ions on trigonal sites in ilmenite structure MgTiO3

Electron spin resonance has been observed for Fe³⁺ and Mn²⁺ ions occupying sites with trigonal symmetry in undoped and doped Verneuil-grown crystals of the ilmenite type compound MgTiO₃. At 300 K, the fine structure parameters in the spin Hamiltonian are (in 10^?4cm^?1) D = +844 (± 1), (a? F) = +118 (± 1), a = 69 (± 7) for Fe³⁺ and D = +164 (± 1), (a ? F) = +10.2 (± l), a = 7.0 (± 1) for Mn²⁺. These values are compared with literature data for Fe³⁺ and Mn²⁺ in other oxides, especially Al₂o₃, with particular reference to the recent “superposition” theory of the effect of a trigonal distortion. From the orientation of the axes of cubic pseudosymmetry of the spin Hamiltonian, and with the assumption that a has the same sign for both ions, it is proposed that Fe³⁺ and Mn²⁺ occupy the same octahedral site, namely the Mg²⁺ site. Anomalous line splittings observed for one sample were attributed to twinning on (0001) or {1120} planes.