Electron Paramagnetic Resonance Of Mn2 Research Articles

Electron Paramagnetic Resonance of Mn2+ Ions in Nanosized Zinc Sulfide with a Planar Lattice Fault

We have studied the EPR of Mn2+ ions in three samples of cubic nano-ZnS made by different technologies and having different nanoparticle sizes. Manganese occurs in the samples as an uncontrolled impurity. The EPR spectra can be described by two components: the spectrum of the Mn2+ in a cubic environment (Mn2+(C)) with parameters g = 2.0022 ± 0.0002, A = (–63.5 ± 0.5)·10–4 cm–1, 0 b4 ≥ 3.5·10–4 cm–1; and the spectrum of the Mn2+ ion associated with a planar lattice stacking fault (Mn2+ (F)), with parameters g = 2.0022 ± 0.0002, A = (–63.5 ± 0.5)·10–4 cm–1, $$ {b}_2^0 $$ = (–36 ± 1)·10–4 cm–1. The ratio of the number of centers Mn2+(C)/Mn2+(F) is 2.1:1 for sample 1 and 1.7:1 for samples 2 and 3. Planar stacking faults are typical lattice faults for cubic nano-ZnS. EPR of the Mn2+ ions lets us monitor the presence of these ions.

Conventional electron paramagnetic resonance of Mn2+ in synthetic hydroxyapatite at different concentrations of the doped manganese

Powders of synthetic hydroxyapatite doped with Mn2+ ions in concentrations from 0.05 till 5 wt. % were investigated by conventional electron paramagnetic resonance (EPR). The parameters of the spin-Hamiltonian are derived. Partially resolved hyperfine structure in the magnetic fields corresponding to g ≈ 4.3 and g ≈ 9.4 is observed. The narrowing of the central peak with concentration is reported. A possibility to use the linewidth and intensity of the central peak for concentration measurements are discussed. The results could be used for the identification and qualification of Mn2+ in oil, mining and ore formations.

The Crystal Structure of Micro- and Nanopowders of ZnS Studied by EPR of Mn2+ and XRD.

The crystal structure of micro- and nanopowders of ZnS doped with different impurities was analyzed by the electron paramagnetic resonance (EPR) of Mn2+ and XRD methods. The powders of ZnS:Cu, ZnS:Mn, ZnS:Co, and ZnS:Eu with the particle sizes of 5–7 μm, 50–200 nm, 7–10 μm, and 5–7 nm, respectively, were studied. Manganese was incorporated in the crystal lattice of all the samples as uncontrolled impurity or by doping. The Mn2+ ions were used as EPR structural probes. It is found that the ZnS:Cu has the cubic structure, the ZnS:Mn has the hexagonal structure with a rhombic distortion, the ZnS:Co is the mixture of the cubic and hexagonal phases in the ratio of 1:10, and the ZnS:Eu has the cubic structure and a distorted cubic structure with stacking defects in the ratio 3:1. The EPR technique is shown to be a powerful tool in the determination of the crystal structure for mixed-polytype ZnS powders and powders with small nanoparticles. It allows observation of the stacking defects, which is revealed in the XRD spectra.

Paramagnetic Manganese in the Atherosclerotic Plaque of Carotid Arteries.

The search for adequate markers of atherosclerotic plaque (AP) instability in the context of assessment of the ischemic stroke risk in patients with atherosclerosis of the carotid arteries as well as for solid physical and chemical factors that are connected with the AP stability is extremely important. We investigate the inner lining of the carotid artery specimens from the male patients with atherosclerosis (27 patients, 42–64 years old) obtained during carotid endarterectomy by using different analytical tools including ultrasound angiography, X-ray analysis, immunological, histochemical analyses, and high-field (3.4 T) pulse electron paramagnetic resonance (EPR) at 94 GHz. No correlation between the stable and unstable APs in the sense of the calcification is revealed. In all of the investigated samples, the EPR spectra of manganese, namely, Mn2+ ions, are registered. Spectral and relaxation characteristics of Mn2+ ions are close to those obtained for the synthetic (nano) hydroxyapatite species but differ from each other for stable and unstable APs. This demonstrates that AP stability could be specified by the molecular organization of their hydroxyapatite components. The origin of the obtained differences and the possibility of using EPR of Mn2+ as an AP stability marker are discussed.

Local zincblende coordination in heteroepitaxial wurtzite Zn1−xMgxO:Mn thin films with 0.01 ≤ x ≤ 0.04 identified by electron paramagnetic resonance

Heteroepitaxial Zn1−xMgxO:Mn thin films show already atx= 0.01 a local cubic zincblende coordination attributed to stacking faults.

Sequential Thermal Decomposition of the Shell of Cubic ZnS/Zn(OH)2 Core–Shell Quantum Dots Observed With Mn2+ Probing Ions

Thermally induced changes in the structure and composition of the shell of tightly aggregated cubic ZnS/Zn(OH)2 core–shell quantum dots of 1.9 nm average core size were investigated by multifrequency electron paramagnetic resonance of Mn2+ probing ions. The observed three-steps temperature induced transformation of the Mn2+ surface centers in the 80–450 °C temperature range was attributed to the sequential decomposition by dehydration of the disordered ε-Zn(OH)2 shell into ZnO, with the formation of the Zn2O(OH)2 and Zn4O3(OH)2 intermediate nanocompounds. The presence of a 0.3 to 1.9 nm thick surface layer of disordered nanomaterial separating the cubic ZnS cores and its shrinking to a few atomic layers by mass loss after annealing up to 350 °C was observed by high resolution transmission electron microscopy. Unlike the single step dehydration around 120 °C of the bulk ε-Zn(OH)2, the complex decomposition of the ε-Zn(OH)2 shell is attributed to its nanosized, disordered structure.

Coherent Raman spectroscopy of the quantum-entangled exciton-Mn2+state in CdTe

Electron paramagnetic resonance of Mn${}^{2+}$ ions in CdTe was detected using coherent Raman electron spin resonance spectroscopy (CRESR) with microwave frequencies of 13.8 and 33.7 GHz. It was possible to resolve the effects of both the hyperfine interaction between the Mn${}^{2+}$ 3${d}^{5}$ electrons and the manganese nucleus and the cubic crystal field. From the optical resonance profile, it is shown that the coherent Raman signal is resonant with an excitonic state and is due to the exchange interactions between the Mn${}^{2+}$ 3${d}^{5}$ electrons and the hole of the exciton. The existence of a CRESR signal under these circumstances provides a direct demonstration that coherence is maintained between the exciton and Mn${}^{2+}$ systems via this exchange interaction.

Electron Paramagnetic Resonance of Mn2+-Doped Cadmium Formate Dihydrate Single Crystals

An electron paramagnetic resonance (EPR) study on Mn2+ doped Cadmium formate dihydrate single crystals is carried out. The EPR spectrum at room temperature exhibits only one out of five fine structural transitions which split into six hyperfine lines in all directions. The spectrum is simulated using the EasySpin program and evaluated spin Hamiltonian parameters. The simulated EPR spectrum is in good agreement with the experiment. By comparing direction cosines of spectroscopic splitting factor g and the direction cosines of different bonds determined by the crystal structure data it is found that Mn2+ enters the lattice substitutionally and only one Mn2+ site is identified. The obtained g and the hyperfine interaction constant A achieved are g = 2.006 ± 0.002, A = (98 ± 2) × 10−4 cm−1 and the second-order axial zero-field splitting parameter D = (60 ± 2) × 10−4 cm−1.

EPR of Mn 2+ in the kagomé staircase compound Mg 2.97Mn 0.03V 2O 8

The electron paramagnetic resonance (EPR) of Mn 2+ in geometrically frustrated Mg 2.97Mn 0.03V 2O 8 single crystals is reported. The complex EPR spectrum shows resonance lines associated with two crystallographically nonequivalent lattice positions of Mn ions that are known in the kagomé staircase system as “cross-tie” and “spine” sites. Additionally, strongly anisotropic resonances of various Mn 2+–Mn 2+ pairs are observed. The signs and values of the crystal field parameters are determined from EPR spectra. The local magnetic symmetry details of magnetic ions and components of the hyperfine structure tensor are determined for various nonequivalent manganese positions. The exchange coupling between Mn ions in “cross-tie” and “spine” sites is found to be J = 41 K.

Electron paramagnetic resonance of Mn2+ ions in CdTe detected by coherent Raman spectroscopy

AbstractWe report the first application of the coherent Raman‐detected ESR spectroscopy (CRESR) technique to a dilute magnetic semiconductor. A bulk crystal of cadmium magnanese telluride with low manganese content was chosen for this study as (Cd,Mn)Te is a well‐characterized model system for which the relevant parameters are accurately known. We consider in detail the information that the CRESR spectra contain on the hyperfine interaction of the Mn2+ 3d5 electrons with the manganese nuclei and the effects of the cubic crystal field. This work opens up the possibility of CRESR studies of other, less well‐known, magnetic semiconductors and their heterostructures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ferroelastic phase transition inK3Na(CrO4)2 single crystals: an electron paramagnetic resonance study

The phase transition in K3Na(CrO4)2 single crystals has been studied by electron paramagnetic resonance (EPR) ofMn2+ ions. The values of the spin-Hamiltonian parameters have beenevaluated. Below the phase transition temperature, the magneticz-axis is deflected in ac and bc crystallographic planes by the same angle. Anomalous lineshapes recorded below the phase transition temperature suggest the existence of anincommensurate phase.

Electron Spin Resonance of Mn2+ in Eu2M”3(NO3)12 · 24H2O (M” = Zn, Co) Single Crystals

Electron spin resonance of Mn2+ doped in Eu2M”3 (NO3)12.24H2O (M” = Zn, Co) single crystals has been studied at 295 and 77 K using an X-band spectrometer. The observation of resolved Mn2+ spectra in Eu2Co3(NO3)12.24H2O at 295 K have been interpreted in terms of random modulation of interaction between Mn2+ and divalent cobalt ions by the rapid spin-lattice relaxation of cobalt ions. T1 of divalent cobalt has been estimated to be ∼ 5×10−12 s at 295 K. The superposition model is applied to the zero-field splitting parameter D.- PACS: 76.30 F

Optical detection of electron paramagnetic resonance in CdMnTe single quantum wells

The electron paramagnetic resonance of Mn2+ ions localized in a CdTe quantum well is measured by an all-optical method. The photoluminescence transitions of a two-dimensional electron gas are used to monitor changes in the Mn spin polarization. The local character of this probe and the detection technique permit us to achieve a very high sensitivity for the number of spins detected (better than 108 spins). Two simultaneous effects are observed at resonance: A blueshift of the whole photoluminescence spectrum, and a dramatic transfer of photoluminescence intensity from neutral to negatively charged excitons.

Resistively detected EPR of Mn 2+ ions coupled to the 2DEG in the quantum Hall regime

An investigation of resistively detected electron paramagnetic resonance (EPR) of Mn 2+ ions imbedded in CdMnTe modulation-doped quantum well structure reveals the strong influence of the 2D-free carriers on the resonance position (Knight shift). The EPR experiments have been performed at low fields and for a ν=3 quantum Hall state. The observed Knight shift at ν=3 is huge and cannot be explained by standard models (mean field approach) of mutual interaction between spins of band electrons and magnetic moments in diluted magnetic semiconductors.

EPR of Mn as densifying agent in SnO 2 powders

Electron Paramagnetic Resonance (EPR) spectra have been obtained at room temperature and at X-band in powders of SnO 2 doped with Mn from 0.3 to 10% and submitted to heat treatment from 500 to 900 °C. Mn ions are probably located at particle surfaces as Mn 2+, evidenced by its single EPR line which narrows by the exchange interaction effect due to particle growth observed by the BET technique. In samples doped above 1% formation of Mn 3O 4 is detected on particle surfaces and a small quantity of Mn is thermally diffused into the bulk as Mn 4+. Powders compacted and sintered at 1300 °C confirmed that Mn 2+ ions remain at grain boundaries acting as densifying agent.

An oscillating manganese electron paramagnetic resonance signal from the S0 state of the oxygen evolving complex in photosystem II.

Photosynthesis produces the oxygen necessary for all aerobic life. During this process, the manganese-containing oxygen evolving complex (OEC) in photosystem II (PSII), cycles through five oxidation states, S0-S4. One of these, S2, is known to be paramagnetic and gives rise to electron paramagnetic resonance (EPR) signals used to probe the catalytic structure and function of the OEC. The S0 states has long been thought to be paramagnetic. We report here a Mn EPR signal from the previously EPR invisible S0 state. The new signal oscillates with a period of four, indicating that it originates from fully active PSII centers. Although similar to the S2 state multiline signal, the new signal is wider (2200 gauss compared with 1850 gauss in samples produced by flashing), with different peak intensity and separation (82 gauss compared with 89 gauss). These characteristics are consistent with the S0 state EPR signal arising from a coupled MnII-MnIII intermediate. The new signal is more stable than the S2 state signal and its decay in tens of minutes is indicative of it originating from the S0 state. The S0 state signal will provide invaluable information toward the understanding of oxygen evolution in plants.

EPR of Mn 2+-ion-doped single crystals of Mg[C 4H 3O 4] 2·6H 2O

Electron paramagnetic resonance of Mn 2+-ion-doped single crystals of magnesium bis(hydrogen maleate) hexahydrate, Mg[C 4H 3O 4] 2·6H 2O, has been studied at room and liquid nitrogen temperatures using X-band frequencies. Two differently oriented but otherwise identical complexes of Mn 2+ ions are found in these crystals. From the observed EPR spectra, spin-Hamiltonian parameters were calculated. It was found that the Mn 2+ ions substitute for Mg 2+ ions. The observed negative shift in g ∥-value of Mn 2+ at room temperature may be due to the polarization effects of the host Mg 2+ ions which produce a local static magnetic field at the Mn 2+sites. The observation of resolved Mn 2+ spectra at room temperature and its broadening on lowering the temperature in Mg(C 4H 3O 4) 2·6H 2O:Mn 2+ single crystals has been explained. The percentage of covalency in the MnO bond has been estimated to be 8%.

Electron paramagnetic resonance of Mn 2+ in Cs 2M(SO 4) 2s6H 2O (M = Mg, Zn, Co, Ni) single crystals

X-band electron paramagnetic resonance measurements are reported on single crystals of Cs 2M(SO 4) 2s6H 2O (M = Mg, Zn, Co, Ni) doped with Mn 2+ ions at 290 K and 77K. Mn 2+ substitutes for divalent cation sites. The spin-Hamiltonian parameters are evaluated. The observation regarding the temperature dependence of linewidth in cobalt salt is discussed in terms of the host spin-lattice relaxation narrowing. The anisotropic and field dependent linewidths of Mn 2+ in nickel salt are discussed in terms of the spin quenching ideas.

Effect of divalent cations on the formation and structure of calcium carbonate polymorphs

The incorporation of divalent cations (Mg2+, Mn2+, Cu2+, Sr2+, Cd2+, Ba2+ and Pb2+) in vaterite and calcite has been studied by atomic absorption spectroscopy (AAS), optical and scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) spectroscopy. The samples of vaterite and calcite were prepared by spontaneous precipitation from aqueous solutions under defined conditions. The particles of vaterite obtained were spheres, being aggregates of crystallites of 25–35 nm, and the crystals of calcite were well defined rhombohedra. All ions examined, except Cu2+, were found to be incorporated in vaterite probably forming solid solutions. Ba2+ caused a distortion of the vaterite crystal lattice and Mg2+ changed the shape of the particles. Mn2+ ions were incorporated into vaterite in at least two different environments, segregated into clusters or substituted for Ca2+, as detected by EPR. The environment of those Mn2+ ions substituted for Ca2+ in vaterite was of lower symmetry than that in calcite. Characteristic EPR spectra of free radicals formed by γ-irradiation of vaterite and calcite are presented. These spectra were used to detect formation of calcite in the vaterite system, in the presence of Cd2+ and Pb2+ ions confirming the results obtained by EPR of Mn2+ as a paramagnetic substitute for Ca2+. Free radicals characteristic of Cd2+ ions, were detected in both vaterite and calcite γ-irradiated under similar conditions.

Electron paramagnetic resonance of Mn 2+ in strained-layer semiconductor superlattices

We report giant crystal field splittings of Mn 2+ electron paramagnetic resonance (EPR) lines observed in ZnTe MnTe and ,nu> CdTe MnTe superlattices. The EPR spectra of isolated Mn 2+ ions diffused into the ZnTe or the CdTe layers provide a direct and precise measure of both the magnitude and the uniformity of strain produced by lattice mismatch between the superlattice constituents.