Physical Principles of the Amplification of Electromagnetic Radiation Due to Negative Electron Masses in a Semiconductor Superlattice

In a superlattice placed in crossed electric and magnetic fields, under certain conditions, the inversion of electron population can appear at which the average energy of electrons is above the middle of the miniband and the effective mass of the electron is negative. This is the implementation of the negative effective mass amplifier and generator (NEMAG) in the superlattice. It can result in the amplification and generation of terahertz radiation even in the absence of negative differential conductivity.Comment: 5 pages, 3 figure

Mössbauer study of the surface of core-shell type nanoparticles

© 2016, Pleiades Publishing, Ltd.The properties of the surface layer of core-shell nanoparticles incorporated into the matrix of macromolecules of 3,4-bis(decyloxybenzoyl) poly(propylene imine) derivative of the second generation are studied by Mössbauer spectroscopy at low temperatures. The spin states, the details of the phonon spectrum and the Debye temperature of surface layer atoms discussed

Blue shift in optical absorption, magnetism and light-induced superparamagnetism in γ-Fe2O3 nanoparticles formed in dendrimer

© 2015, Springer Science+Business Media Dordrecht. Abstract: We are presenting the investigation of the optical, magnetic, and photoinduced superparamagnetic properties of single-domain γ-Fe2O3 nanoparticles (NPs) with diameters of about 2.5 nm formed in second-generation poly(propylene imine) dendrimer. The optical absorption studies indicated direct allowed transition with the band gap (4.5 eV), which is blue shift with respect to the value of the bulk material. Low-temperature blocking of the NPs magnetic moments at 18 K is determined by SQUID measurements. The influence of pulsed laser irradiation on the superparamagnetic properties of γ-Fe2O3 NPs was studied by EPR spectroscopy. It has been shown that irradiation of the sample held in vacuo and cooled in zero magnetic field to 6.9 K leads to the appearance of a new EPR signal, which decays immediately after the irradiation is stopped. The appearance and disappearance of this new signal can be repeated many times at 6.9 K when we turn on/turn off the laser. We suppose that the generation of conduction band electrons by irradiation into the band gap of the γ-Fe2O3 changes the superparamagnetic properties of NPs. Graphical Abstract: [Figure not available: see fulltext.]Features of the behavior of single-domain γ-Fe2O3 nanoparticles formed in dendrimer were found by UV-Vis and EPR spectroscopy: “blue” shift in optical absorption, a significant increase in the band gap width and variation of superparamagnetic properties under light irradiation

Magnetic Properties of Novel Dendrimeric Iron(III) Complexes of the First Generation: EPR and Mössbauer Study

© 2016, Springer-Verlag Wien.The magnetic properties of novel liquid-crystalline dendrimeric iron(III) complexes of the first generation, [Fe(L2)]+X−, where L = 3,4,5-tri(tetradecyloxy) benzoyloxy-4-salicyliden-N′-ethyl-N-ethylenediamine and X = Cl, NO3 have been investigated for the first time by electron paramagnetic resonance (EPR) and Mössbauer spectroscopy in the wide (4–300 K) temperature range. It has been shown that each compound consists of two types of iron centers: low-spin (LS, S = 1/2) and high-spin (HS, S = 5/2). A partial thermally driven spin transition (S = 5/2 ↔ 1/2) was observed in these complexes. EPR showed that the LS and HS iron centers are coupled by weak antiferromagnetic interactions and most probably form a chain in the column. Mössbauer spectroscopy confirmed the existence of the LS and HS Fe(III) centers in the compounds, a partial spin crossover of approximately 2–8 % of the Fe(III) molecules and showed that the HS Fe(III) centers demonstrate the antiferromagnetc type of ordering at 5 K

Detailed EPR study of spin crossover dendrimeric iron(III) complex

The unusual magnetic behavior of the first dendritic Fe3+ complex with general formula [Fe(L)2]+Cl -·H2O based on a branched Schiff base has been investigated by electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. EPR displays that complex consists of the three types of magnetically active iron centers: one S = 1/2 low-spin (LS) and two S = 5/2 high-spin (HS) centers with strong low-symmetry and weak distorted octahedral crystal fields. Analysis of the magnetic behavior reflected by I versus T (where I is the EPR lines integrated intensity of the spectrum) demonstrates that the dendritic Fe3+ complex has sufficiently different behavior in three temperature intervals. The first (4.2-50 K) interval corresponds to the antiferromagnetic exchange interactions between LS-LS, LS-HS, and HS-HS centers. The appearance of a presumable magnetoelectric effect is registered in the second (50-200 K) temperature interval, whereas a spin transition process between LS and HS centers occurs in the third (200-330 K) one. The coexistence of the magnetic ordering, presumable magnetoelectric effect, and spin crossover in one and the same material has been detected for the first time. The Mössbauer spectroscopy data completely confirm the EPR results. © 2013 American Chemical Society

Optical properties and photoinduced superparamagnetism of γ-Fe<inf>2</inf>O<inf>3</inf> nanoparticles formed in dendrimer

© 2014 Elsevier Ltd. All rights reserved. We are presenting the joint investigation of the optical and photoinduced superparamagnetic properties of a single-domain γ-Fe2O3 nanoparticles (NPs) formed in poly(propylene imine) (PPI)-dendrimer. The optical absorption studies indicated direct allowed transition with the band gap (4.5 eV), which is blue-shift with respect to the value of the bulk material. The influence of pulsed laser irradiation on the superparamagnetic properties of γ-Fe2O3 NPs was studied by Electron paramagnetic resonance (EPR) spectroscopy. It has been shown that irradiation of the sample in vacuo and cooled in zero magnetic field to 6.9 K leads to the appearance of a new EPR signal, which decays immediately after the irradiation is stopped. We suppose that the generation of conduction band electrons by irradiation into the band gap of the γ-Fe2O3 changes the superparamagnetic properties of NPs

Coexistence of spin crossover and magnetic ordering in a dendrimeric Fe(III) complex

© 2015 AIP Publishing LLC. The magnetic properties of a new dendrimeric spin crossover Fe(III) complex, [Fe(L)2]+PF6, where L = 3,5-di[3,4,5-tris(tetradecyloxy) benzoyloxy]benzoyl-4-salicylidene-N-ethyl-N-ethylene-diamine, are reported for the first time. EPR studies show that this compound undergoes a gradual spin transition in the temperature range 70-300K and has antiferromagnetic ordering below 10K. Mössbauer spectroscopy at 5K confirms the presence of magnetic ordering in the dendrimeric iron complex

Electrophysiological Parameters of Sinus Node Function in Patients with Paroxysmal Tachyarrhythmias

to analyze the indicators of the function of the sinus node in patients of young age with paroxysmal tachycardia. Methods: study included 11 patients with suspected paroxysmal tachycardia, with an average age of 17±28. The basis for holding transesophageal electrophysiological study (TE EPS) was the clinical and electrophysiological characteristics of paroxysmal tachycardia. According to the results of Holter monitoring ECG (HM ECG) analyzed the minimum and maximum heart rate, number of ventricular and supraventricular arrhythmias, presence of pauses, rhythm and episodes of paroxysmal tachycardia. According to CHP, EFI estimated the initial heart rate (HR), recovery time of sinus node function (RTSNF), corrected recovery time of sinus node function (CRTSNF), point of Wenkebach (p. W), duration of the effective refractory period of the atrioventricular connections, presence of aberrant complexes and episodes of paroxysmal tachycardias before and after administration of atropine at a dose of 0.02 mg/kg. Results: Complaints characteristic of the tachyarrhythmia was diagnosed in 9 patients, episodes of heart rate more than 150 beats per minute in 7 patients. When conducting TE EPS obtained the following results: episodes of supraventricular tachycardia provoked in 8 patients (in two cases of paroxysmal tachycardia managed to provoke only after administration of atropine). Three of them have shimmer and atrial flutter episodes reciprocal tachycardia in five. Three patients provoke paroxysmal tachycardia failed, but they showed a shortening of the PQ interval and the appearance of aberrant QRS complexes when stimulated. In patients with paroxysmal SVT signs of sinus node dysfunction was detected in 6 patients, in the form of episodes of sinus arrhythmia (4 patients), migration pacemaker the atria (4 patients), sinoatrial blockade of II degree (3 patients), blockade of legs of bunch of gisa (2 patients), atrioventricular block degree II-III (1 patient), RTSNF more than 1500 MS in 1 patient, CRTSNF greater than 500 msec in 3 patients. Conclusion: in 6 of 9 patients with supraventricular paroxysmal tachycardia revealed signs of sinus node dysfunction, probably has a vagotonic in nature

Magnetic Phase Separation and Magnetic Moment Alignment in Ordered Alloys FE 65

The structure and the magnetic state of ordered Fe65Al35-xMx (Mx = Ga, B; x = 0; 5 at.%) alloys are investigated using X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. The behavior of the magnetic characteristics and Mössbauer spectra of the binary alloy Fe65Al35 and the ternary alloy with gallium addition Fe65Al30Ga5 is explained in terms of the phase separation into two magnetic phases: a ferromagnetic one and a spin density wave. It is shown that the addition of boron to the initial binary alloy Fe65Al35 results in the ferromagnetic behavior of the ternary alloy

Structural, magnetic and dynamic characterization of liquid crystalline iron(III) Schiff base complexes with asymmetric ligands

The iron(III) complexes that were formed by coordination of the Fe III ion with the asymmetric tridentate liquid crystalline Schiff base ligand (L), the water molecules and the different counterions [PF 6 - (1), NO3 - (2), and Cl- (3)] were studied by electron paramagnetic resonance (EPR) spectroscopy. EPR spectroscopy demonstrated that each of the complexes investigated consists of two types of iron centers: S = 1/2 low-spin (LS) and S = 5/2 high-spin (HS). LS iron complexes 2, 3 and LS complex 1 in the temperature range 4.2-250 K have a (dxz,dyz)4(dxy)1 ground state. Interesting features werefound for the monocationic FeIII complex 1, [Fe(L)X(H2O)2]+X-, with X = PF6 - as the counterion. The LS and HS iron centers of 1 are coupled together antiferromagnetically and form a dimer structure by means of the water molecules and the PF6 - counterion. The second-type of LS and HS centers that are visible by means of EPR spectroscopy were best observed in the liquid crystalline (387-405 K) phase. The monitoring and the simulation of the EPR spectra enabled us to trace the dynamics of changing the number of the second-type of LS centers with respect to the first-type of LS centers. The observed dynamic process is characterized by the enthalpy value ΔH = 27.9 kJ/mol, which was caused by reorientation of the PF6 - counterion. Calculation of the observed g values for the second-type of LS complex 1 indicated that, in this case, the (d xy)2(dxz,dyz)3 ground state is stabilized. The conversion between the electron (dxz,d yz)4(dxy)1/(dxy) 2(dxz,dyz)3 configurations was found to be temperature dependent and was detected in the same material for the first time in iron complexes. We synthesized a novel compound, namely a liquid crystalline iron(III) Schiff base complex with the asymmetric ligand [Fe(L)X(H2O)2]+X-, where X = PF 6 - is the counterion. This compound has a labilelow-spin electron configuration that switches between the (dxz,d yz)4(dxy)1/(dxy) 2(dxz,dyz)3 ground states and is temperature-dependent. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim