Electron spin resonance of Mn2+ in NaCl single crystal and lattice defects

The electron spin resonance spectra of Mn²⁺ in NaCl single crystals are investigated in detail. Seven different spectra (I, II, III₁, III₂, IV, V and VI) are observed. The spectra I–IV are the same as those observed by earlier workers, while the spectra V and VI are observed here for the first time. The local symmetry at the paramagnetic ion is orthorhombic for the spectra IV and V and tetragonal for the spectrum VI about the crystallographic [001] direction. The properties of the spectrum IV are explained in terms of an associated pair Mn²⁺: O₂ ^2? with O₂ ^2? molecular ion at the nearest neighbour anion site in the [001] direction with its internuclear axis in the (001) plane. The spectrum V is assigned to the associated pair Mn²⁺: O₂ ^2? coupled with a nearby cation vacancy in the [001] direction and the spectrum VI to Mn²⁺ ion associated with OH^? ion at the anion site in the [001] direction with a probable second neighbour cation vacancy. All the observed spectra are analysed in terms of the parameters of the usual spin-Hamiltonian.     

Paramagnetic resonance of Mn2+ in KNO3 single crystal: Motional effects

The electron paramagnetic resonance of Mn²⁺ in KNO₃ single crystal is investigated over a temperature cycle through transition temperatures. The hyperfine coupling constant, A, half width,Δ H, and the line intensity, I, are found to show sudden changes at the transition temperature, at whichα-KNO₃ changes intoβ-KNO₃. The lines are much sharper in the high temperatureβ-phase than inα-phase of the crystal. They are explained, qualitatively, in terms of structure change and rotation of NO ₃ ^? ions. The spectra in the two phases,α andβ, are analysed in terms of usual spin-Hamiltonian. A search of metastableγ-phase is also made and probable indications for the same are found.     

Electron paramagnetic resonance of Mn2+ in (NH4)2SO4 single crystal

Electron paramagnetic resonance investigation of Mn²⁺ in (NH₄)₂SO₄ single crystal is discussed both in paraelectric and ferroelectric phases of the crystal. Mn²⁺ is found to substitute one of the two possible types (α andβ) of NH ₄ ⁺ ions and get associated with the second type of NH ₄ ⁺ vacancy, the vacancy being the second distant neighbour in thebc-plane. As The line joining Mn²⁺ substituted NH ₄ ⁺ site and NH ₄ ⁺ vacancy lies at an angle of 18° from the crystallographicb-axis in thebc-plane. As the temperature is lowered to ? 56° C the crystal becomes ferroelectric and the spectrum in the paraelectric phase splits into two from which it appears that two sets of Mn²⁺ sites which are magnetically equivalent in the paraelectric phase become inequivalent in the ferroelectric phase. The spin Hamiltonian analysis is presented for the spectrum in the paraelectric phase.     

Electron paramagnetic resonance of Mn2+ in NaF single crystals

The electron paramagnetic resonance of Mn²⁺ in NaF single crystals is investigated at different temperatures from 573° K to 93° K. Four different spectra designated as I, II, III₂ and III₄ are observed. Spectrum I consists of a single broad resonance corresponding to precipitated Mn²⁺ ions. Spectrum II is isotropic and centred nearg = 2.00. This spectrum corresponds to substitutional Mn²⁺ ions with remote charge compensating sites and therefore with local cubic symmetry. Spectrum III₂ withg = 2.014 and spectrum III₄ withg = 1.995 are also due to substitutional Mn²⁺ ions but subjected to tetragonal crystalline fields and are the same as those reported by earlier workers. Superhyperfine structure has been observed in spectra II, III₂ and III₄. The analysis of that structure in spectra II and III₂ has been carried out for the first time and the constants A_s, and A_σ are given. The spectra are analysed by the usual spin-Hamiltonian method.     

Electron paramagnetic resonance studies of VO2+ in single crystals of NaCl,KCl and RbCl

Electron paramagnetic resonance (EPR) of VO²⁺ radicals incorporated in face-centred single crystals of NaCl, KC1 and RbCl has been studied in the temperature range of 77° K to 330° K. At liquid nitrogen temperature, anisotropic spectra have been recorded in each case while spectra recorded at room and higher temperatures are isotropic suggesting the existence of a fast readjustment of VO²⁺ molecular ions in the crystals at higher temperature while this motion gets hindered at liquid nitrogen temperatures. Spin-Hamiltonian constants are calculated from the recorded isotropic and anisotropic spectra. The line widths in each case are found to obey a parabolic law originally proposed by Kivelson. The constants which give a close fit have been evaluated. The random orientation and readjustment of V-0 bond in these alkali chloride crystals is explained on the assumption that the medium exhibits a “liquid-like” nature for VO²⁺ molecular ion as far as the electron paramagnetic resonance absorption is concerned.     

Electron paramagnetic resonance of CU2+ ion in CsCl single crystals

Electron paramagnetic resonance spectrum of the Cu²⁺ ion in CsCl is studied at different temperatures. The local symmetry at the Cu²⁺ site is found to be tetragonal. A model of substitutional Cu²⁺ ion associated with a first neighbour cation vacancy is proposed to explain the observed spectrum.     

Electron spin resonance of Cr5+ in CaWO4

Electron Spin Resonance of CaWO₄ with 0·1% of Cr has been investigated at liquid nitrogen and liquid helium temperatures. The observed ESR spectrum is attributed to Cr⁵⁺ ion in the substitutional site of W which has a compressed tetrahedral surroundings. A simple point charge calculation based on this geometry explains the observedg anisotropy and hyperfine anisotropy and places the magnetic electron in a predominantly \(3d_{z^2 } \) orbital. A comparison of these results with those obtained on other isoelectronic systems in similar and different co-ordinations justifies our assignment.     

Electron paramagnetic resonance of mn2+ in single crystals of Cesium Sulphate

Electron paramagnetic resonance (EPR) of divalent manganese ion has been studied at 9.5 KMc/sec. These studies reveal that Mn²⁺ ion substitutes at a β-Cs⁺ site and gets associated with a vacancy at a neighbouring β-Cs⁺ site in the aft-plane. Thez-axis of this ββ complex makes an angle of 25° with the crystallographicb-axis. The spectra observed have been described by the spin-Hamiltonian for Mn²⁺ in rhombic crystalline field. The temperature dependence of the parameters D and E has been studied in the range 293°–77° K. The spectra for the observed complex along its three-principal axes have been analysed using second order perturbation equations. The spin-Hamiltonian parameters obtained from the spectra taken at room temperature are: $$\begin{gathered} g_z = 2 \cdot 000 \pm 0 \cdot 003, g_x = 2 \cdot 015 \pm 0 \cdot 003, g_y = 2 \cdot 000 \pm 0 \cdot 003; \hfill \\ A_z = - 93 \pm 1, A_x = - 91 \pm 1, and A_y = - 91 \pm 1 G; \hfill \\ D = - 941 \pm 3 and E = - 14 \pm 4 G; \hfill \\ b^\circ _4 = \left( {0 \cdot 0} \right), b_4 ^2 = \left( {13} \right), and b_4 ^4 = - 77 \pm 5 G \hfill \\ \end{gathered} $$      

The distortion of electron spin resonance signal shapes by finite modulation amplitudes

Zusammenfassung Der Einfluss des Detektorsystems eines Elektronenresonanzspektrographen auf die Verzerrung des Signals wird in abhängigkeit der Modulationsamplitude untersucht. Es werden zwei Detektorsysteme verglichen: 1. quadratischer und phasenempfindlicher Detektor, 2. zwei phasenempfindliche Detektoren. Die Ausgangssignale werden als Kombinationen der Fourierkoeffizienten der ursprünglichen Absorptionsbande dargestellt. Eine Formel für die Fourierkoeffizienten einer allgemeinen Absorptionsbande wird hergeleitet und auf den Fall der Lorentz-Bande angewendet. Im Fall 2 ergeben sich Absorption und Dispersion des integrierten Empfangssignals als Hilbert-Transformierten einer einfachen komplexen Funktion.—Das Verhältnis der signal to noise ratios von Fall 1 und 2 wird ebenso diskutiert. Die wesentlichen Resultate sind graphisch dargestellt.     

An investigation into the mechanism of ice crystal nucleation by proton spin resonance spectroscopy

Zusammenfassung Unter Heranziehung der Kernresonanzspektroskopie wird versucht, den Vorgang der Keimbildung an Eiskeimbildungskernen wie AgI und CuO abzuklären. Die Ergebnisse der ersten Versuche zeigen, dass die adsorbierte Wasserschicht unterhalb einer bestimmten Temperatur, die nahe der Schwellentemperatur für die Elskeimbildungsaktivität liegt, teilweise in einem flüssigkeitsartigen und teilweise in festkörperartigem Zustand auftritt. Bei abnehmender Temperatur wächst der feste Anteil der Schicht auf Kosten des flüssigen Bestandes. Der volle Verfestigungsvorgang wickelt sich dabei in einem Temperaturbereich von ca. 20°C ab. Die Beobachtungen legen es nahe, anzunehmen, dass zwischen dem Auftreten der eisartigen Struktur in der adsorbierten Schicht und der Eisbildungswirksamkeit der Kernstoffe eine Beziehung besteht.     

Paramagnetic resonance of Gd3+ in SmCl3·6H2O single crystals

The Paramagnetic Resonance of Gd³⁺ in SmCl₃·6H₂O single crystals, grown from solution, is studied at room temperature. A six line spectrum for H//Z and a seven line spectrum for H//X corresponding to ΔM=± 1 transitions are observed. Their angular variation in ZX plane from?=0° to?=90°, is studied and the spin-Hamiltonian analysis is presented. The probable amount of admixture of the next higher electronic state⁶P_7/2 with the ground state⁸S_7/2 is also estimated.     

Mathematical analysis of plasmonic resonance for 2-D photonic crystal

In this article, we study the plasmonic resonance of infinite photonic crystal mounted by the double negative nanoparticles in two dimensions. The corresponding physical model is described by the Helmholz equation with so called Bloch wave condition in a periodic domain. By using the quasi-periodic layer potential techniques and the spectral theorem of quasi-periodic Neumann–Poincaré operator, the quasi-static expansion of the near field in the presence of nanoparticles is derived. Furthermore, when the magnetic permeability of nanoparticles satisfies the Drude model, we give the conditions under which the plasmonic resonance occurs, and the rate of blow up of near field energy with respect to nanoparticle's bulk electron relaxation rate and filling factor are also obtained. It indicates that one can appropriately control the bulk electron relaxation rate or filling factor of nanoparticle in photonic crystal structure such that the near field energy attains its maximum, and enhancing the efficiency of energy utilization.     

Growth of Cu2Cl2 and Cu2Br2 on single crystal faces and polycrystalline copper during dissolution in CuSO4 + H2SO4

Cu₂Cl₂ and Cu₂Br₂ precipitate and crystallise in the form of triangular pyramids and dendrites when Cu is immersed in aerated, acid CuSO₄ solution containing HC1 or HBr. The critical concentration of HC1 or HBr for this precipitation depends on the surface of the copper: Poly-crystalline < (110) < (100) < (111). In the deaerated solution there is no precipitation of Cu₂Cl or Cu₂Br₂ even at a high concentration of HC1 or HBr when only preferential etching occurs.     

Paramagnetic resonance of Gd3+ in Sm (NO3)3. 6H2O single crystals

The paramagnetic resonance of Gd³⁺ in Sm(NO₃)₃.6H₂O single crystals, grown from solution, is studied at room temperature. A seven line spectrum for H//Z as well as for H//X corresponding to ΔM=±1 transitions are observed. The spin Hamiltonian analysis is presented.     

Growth of GaSb single crystal in space

The crystal growth under microgravity condition in space has attracted a lot of attention, for the quality of crystals can be improved under microgravity because it creates an environment where nature convection is suppressed and mass transportation is controlled by diffusion. This is a joint work between Institute of Physics, the Chinese Academy of Sciences and Department of Electronics Engineering, the University of Tokyo. A rod of GaSb single crystal doped with Te, whose diameter is 6 mm and length is 30 mm, was grown in space during the China returnable satellite mission No. 14 in 1992. The research results show that there was no striations in the space-grown crystal part, and furthermore the dislocation density was close to zero in the part where melt was not in contact with quartz wall during the crystal growing in the space, but it increased rapidly after the melt was in contact with the wall. This paper summarizes the growth and research results of the GaSb crystal in detail, and analyzes the influences of microgravity on crystal growth and its potential developments in the future.     

EPR study of ZnS:Mn2+ nanocrystals and pyrex glasses

Pyrex glasses with different ZnS: Mn²⁺ contents were prepared by melting method. It has been found that Mn ion may occupy two sites: (Mn²⁺)_sub, and (Mn²⁺)_int from photoluminescene (PL) and photoluminescence excitation (PLE) spectra. The results were confirmed by the further electron panmagnetic resonance (EPR) experiments and the three types of states (Mn²⁺)_sub, (Mn²⁺)_int,and Mn clusters were identified. It was observed that theg-factor and the hyperfine structure (HFS) constant increase with the decreasing size of nanocrystallite. This may result from hybridization of sp³ electron states of ZnS and 3d⁵ electron states of Mn by the effects of quantum confinement and the surface states. Project supported by the National Natural Science Foundation of China and Laboratory of Excited State Processes, Chinese Academy of Sciences.     

Paramagnetic resonance studies of Cu2+ doped in NH4Br

Electron Paramagnetic Resonance studies of Cu²⁺ doped in NH₄Br single crystals have been carried out for the first time. The room temperature data reveal that Cu²⁺ ions go predominantly to interstitial sites having square planar co-ordination of four Br^? ions. For this type of complexes the bromine: superhyperfine structure: is observed on the normal hyperfine structure lines of copper. Existence of other weak spectra indicates that a relatively few Cu⁺⁺ ions go substitutionally to (NH₄)⁺ ions, and are probably associated with a first or a second nearest neighbour cation vacancy, among the two, the latter being more predominant. However, the low temperature studies corresponding to the tetragonal phase of NH₄Br indicate that a number of Cu²⁺ ions at interstitial sites get readjusted to the lattice sites after phase transformation. The spectra in both the phases are analysed by the usual spin Hamiltonian method.