Magnetic Spin Effects Research Articles

Photoinduced Room-Temperature Magnetism of Low Curie Temperature Cu–Ni Nanoparticles in Polymer Composites with Rubrene Microcrystals

A relation has been established between the decrement of the low-field magnetic spin effect (measured by the luminescence of polymer films of composites with rubrene microcrystals), caused by the addition of magnetic Cu–Ni nanoparticles with a low Curie temperature (TC = 40–60°C), and the photoinduced particle magnetic moment exceeding the dark moment. Based on the study of the temperature dependence of the decrement and its comparison with the thermal demagnetization of the dark magnetic moment, a conclusion was made about a possible mechanism for the photothermal magnetization of nanoparticles

Ultrafast Pump‐Probe Spectroscopy—A Powerful Tool for Tracking Spin‐Quantum Dynamics in Metal Halide Perovskites

AbstractUltrafast pump‐probe spectroscopy provides a powerful tool for deep insight into sophisticated electron–hole dynamics for materials development and devices optimization, particularly for emerging metal halide perovskites (hereafter, termed perovskites), due to their great potentials for optoelectronic and photonic applications in solar cells, light‐emitting diodes, photodetectors, and lasers. Recently, flourishing spin‐related photophysical phenomena (such as, Rashba effect, optical Stark effect, and magneto­optical effect) in perovskites and their relevant devices have experimentally been observed, attributed to huge spin‐orbital coupling effect and strong interaction of electron–photon in perovskites. However, fundamental understanding of spin‐dependent photophysics in perovskites is still at its nascent stage. In recent few years, circularly‐polarized ultrafast pump‐probe technique has pushed burgeoning development of spin‐selective photophysics in perovskites for spintronic device applications. Nevertheless, few review papers summarize this emerging field systematically, completely, and insightfully. Herein, to evoke broader attraction and research interest, recent advances in spin‐quantum dynamics in perovskites revealed by circularly‐polarized pump‐probe technique are reviewed: from the fundamentals and theories of circularly‐polarized ultrafast pump‐probe transient absorption and time‐resolved Faraday rotation spectroscopy; to the recent enlightening works on spin relaxation dynamics, spin‐selective exciton optical Stark effect, magnetic spin effect, and spin polarization dynamics. Finally, current challenges and perspectives are given.

Magnetic Spin Effects in Photoprocesses inside Polymeric Photoconductors

Magnetic spin effects are detected and studied in the processes of sensitized current-carrier photogeneration and luminescence inside polymer photoconductor films based on polyimides and composites of polymers with carbazole moieties combined with electron acceptors (chemical sensitization) and dyes (spectral sensitization). The effect an electric field has on the quantum yield of photogeneration and the luminescence of excited charge-transfer complexes (reversible and irreversible effects) at spectral sensitization is studied in the presence of O2.

Decrement of magnetic spin effect in films of polymer composites with rubrene: Interaction of excited states with magnetic nanoparticles

For films of poly(alkane etherimide) composites containing rubrene microcrystals, the effect of Cu–Ni magnetic nanoparticles (MNP) with a reduced Curie temperature T C (40–60°C) on luminescence and photoconductivity, as well as on the magnetic spin effect, has been observed and studied. It has been shown that this effect depends on the excitation intensity and weak heating (up to T < T C°C). The assumption has been made that the excited states of the microcrystals (or charge carriers) interact with the MNP surface, leading to a change in their magnetic characteristics.

Possible Mechanisms Underlying the Therapeutic Effects of Transcranial Magnetic Stimulation.

Transcranial magnetic stimulation (TMS) is an effective method used to diagnose and treat many neurological disorders. Although repetitive TMS (rTMS) has been used to treat a variety of serious pathological conditions including stroke, depression, Parkinson’s disease, epilepsy, pain, and migraines, the pathophysiological mechanisms underlying the effects of long-term TMS remain unclear. In the present review, the effects of rTMS on neurotransmitters and synaptic plasticity are described, including the classic interpretations of TMS effects on synaptic plasticity via long-term potentiation and long-term depression. We also discuss the effects of rTMS on the genetic apparatus of neurons, glial cells, and the prevention of neuronal death. The neurotrophic effects of rTMS on dendritic growth and sprouting and neurotrophic factors are described, including change in brain-derived neurotrophic factor concentration under the influence of rTMS. Also, non-classical effects of TMS related to biophysical effects of magnetic fields are described, including the quantum effects, the magnetic spin effects, genetic magnetoreception, the macromolecular effects of TMS, and the electromagnetic theory of consciousness. Finally, we discuss possible interpretations of TMS effects according to dynamical systems theory. Evidence suggests that a rTMS-induced magnetic field should be considered a separate physical factor that can be impactful at the subatomic level and that rTMS is capable of significantly altering the reactivity of molecules (radicals). It is thought that these factors underlie the therapeutic benefits of therapy with TMS. Future research on these mechanisms will be instrumental to the development of more powerful and reliable TMS treatment protocols.

Photostimulated currents and magnetic spin effects in organic p-n polymeric heterostructures

Generation of charged current carriers in photovoltaic cells with polymeric p-n heterostructures as an active layer was studied. Photo- and thermofield stimulation of Pool-Frenkel type states at the p-n interface of polymeric heterostructures based on p (doped polyimides) and n type (doped carbazolyl-containing polymers and polyesteramides) was found to cause the generation of current carriers and observation of photostimulated currents. These states are interpreted as stabilized pairs of charges consisting of carriers captured by deep charged centers with the opposite sign. They are presumably formed at the interface as a result of an irreversible photochemical reaction of the free radical type of a radical-ion pair, which appears in the phototransfer of an electron from a donor polyimide fragment to an excited dopant particle. The effectiveness of the formation and accumulation of these states was found to increase as the surface area and the degree of interface development (sharp, diffuse, volume) grew. Photostimulated currents were shown to influence the photovoltaic characteristics of cells based on polymeric p-n heterostructures: an increase in short circuit photocurrent (by more than an order of magnitude for a volume interface and by several times for a diffusion interface) was observed, and free running voltage increased (to 1.2–1.4 V). This allows the energy effectiveness of photovoltaic cells to be substantially increased at a moderate increase in temperature (by no more than 20–30°C), in particular, because of nonactinic light source IR radiation. The formation of ion-radical pairs and their relation to Pool-Frenkel states is substantiated by observed positive magnetic field influence (H < 1 kOe, T = 293−323 K) on the yield of luminescence of dopant particles and photostimulated current (magnetic spin effects by the hyperfine interaction mechanism).

The effect of reagent structure and the medium on radical pair recombination in polymers

Triarylcarbinols, the recombination products of ketyl and aminyl radicals identified by visible absorption spectra as relevant triarylmethane dyes, are formed during irradiation of poly(methyl methacrylate), poly(vinyl chloride), polystyrene and cellulose triacetate films containing substituted benzophenones and aromatic amines. Quantum yields of the reactions are determined. The features of reagents and polymer structures effect on the formation rates and yields of products are discussed. The reaction only proceeds in local zones of relatively large (∼ nm) size, as is found based on the analysis of quantum yield dependence on amine concentration. This stipulates the presence of magnetic-spin effects leading to a significant (by 10–20%) product accumulation rate decrease in poly(vinyl chloride) and polystyrene as external magnetic field is applied. A mechanism of significant photochemical post-effect in films produced from chlorine-containing solvent is suggested and kinetic description is proposed. The formation of dye at irradiated film treatment by HCl is diffusion limited. This allows using the reactions studied in the investigations of both slow and fast diffusion processes in polymers.

Magnetic field effects on the yields of dyes in sensitized transformation of diphenylamine in micellar systems

A strong influence (an increase in the rate of formation of the diphenylbenzidine dication by up to three times) of an external magnetic field on the yields of colored products was observed when micellar solutions of benzophenone and diphenylamine derivatives were UV irradiated in the presence of acids. A mechanism of the phenomenon was suggested. The mechanism by based on the concept of the simultaneous occurrence of two processes, (1) geminate recombination of ketyl and aminyl radicals with the formation of triarylmethane dye and (2) bulk recombination of two radical cations produced in the protonation of aminyl radicals with the formation of the diphenylbenzidine dication. Magnetic field is a factor determining the rate of the triplet-singlet conversion of radical pairs formed in the photoreduction of the ketone by amine and, therefore, the ratio between the stationary concentrations of aminyl radicals and radical cations. The influence of the structure of ketones, the ratio between the reagents and surfactant, and the pH value on the dye yield and the scale of magnetic-spin effects were analyzed.

Mass‐independent fractionation of mercury isotopes in the environment

The toxicity of mercury's methylated species and its biomagnification in aquatic food chains and global dispersion by the atmosphere are the cause of worldwide health problems. Recent reports have observed natural mass‐dependent fractionation in mercury isotopes, and recent theoretical work has demonstrated that isotopic separation in mercury is due primarily to nuclear field shifts (nuclear volume effect), and the magnetic spin effect gives rise to mass‐independent fractionation (MIF) of odd neutron number isotopes. Now we present analytical evidence of mass‐independent isotopic variations in mercury produced by both nuclear volume and magnetic isotope processes. Even mass number isotopes exhibit a pattern indistinguishable from that produced by mass‐dependent fractionation, with both positive and negative 199Hg and 201Hg anomalies. MIF is easier to reliably determine in Hg isotopes than mass‐dependent fractionation alone, and thus it provides a potentially important key in constraining models of mercury sources and pathways in the environment.

Magnetic Spin Effects in Enzymatic Reactions: Radical Oxidation of NADH by Horseradish Peroxidase

A description of the elementary steps of the horseradish peroxidase (HRP)-catalyzed oxidation of NADH is presented, along with a quantitative analysis of the magnetic-field dependence of the enzymatic reaction. In the absence of H(2)O(2), the catalytic cycle begins with single-electron transfer from NADH to native HRP to form the NADH(.+) radical cation and the ferroperoxidase intermediate (Per(2+)). The theoretical framework for the magnetic-field dependent recombination of radical pairs has been extended to describe the magnetic-field dependence of reaction rate constants for multi-spin paramagnetic pairs, including the NADH(.+) radical cation and Per(2+) that exist in a correlated quartet electronic spin state. Good agreement between the experimentally observed and the theoretically calculated magnetic-field dependences of the effective rate constants underlines the importance of the initial single-electron-transfer step and supports a model in which the catalytic cycle begins with the one-electron reduction of HRP by NADH.

Ligand dependence of magnetic spin effects on photooxidation of [Ru(bpy) 3− n(CN) 2 n] (+2−2 n) type complexes

Photoinduced electron transfer reaction from the series of [Ru(bpy) (3− n) (CN) 2 n ] (2+−2 n) complexes ( n=0, 1, 2) to methylviologen has been investigated using external magnetic field modulation in order to obtain relevant kinetic parameters for spin relaxation, backward electron transfer and cage escape of the geminate radical pair. The replacement of one bpy by two cyanide ligands results in an increase of the quenching rate constant and a decrease of the cage escape efficiency. The latter is decreased in a magnetic field and the sensitivity of this effect is weakened by introducing CN − ligands. From the analysis of the magnetic field dependence it can be inferred that with increasing number of CN − ligands, backward electron transfer rate and spin relaxation time in the geminate radical pair exhibit a moderate decrease but that the rate constant of cage escape decreases very strongly.

Effect of Electron Delocalization on Charge Separation in Photoconductive Aromatic Polyimides with Pronounced Electron Donor-Acceptor Interaction

The comparison of charge carrier photogeneration quantum yields β and their field dependencies is carried out for three series of soluble photoconductive polyimides (PIs) based on 4,4′-diaminotriphenylamine (I), N,N′-bis(p-aminophenyl)-N,N′-diphenyl-p-phenylenediamine (II) and N,N′-bis(p-aminophenyl)-N,N′-diphenylbenzidine (III) which differ only by the donor chain fragment size at the same acceptor diimide fragments. In comparison with PIs I series for PIs II and III series the significant increase of β value (by 1–2 orders of magnitude) and initial charge separation distance r o in ion-radical pairs (IRP) (from 2 to 3,5-3,8 nm) are found. This increase is due not only to rising density of hole transporting sites but more likely to the efficient delocalization of the positive charge within the extended conjugation system of the donor fragment during IRP formation process. This conclusion is evidenced by the observation of magnetic spin effect (MSF) on photoconductivity which enables to estimate the charge delocalization length in these PIs.

Electric field dependence of the magnetic spin effect in the photoproduction of charge carriers in polydiacetylene

It is shown that the external-electric-field dependence of the magnitude of the magnetic spin effect in the photoproduction of charge carriers in polydiacetylene films external-electric-field is attributable to a distribution of weakly bound electron-hole pairs with respect to the initial pair separations, within which the pair lifetimes compete with the characteristic times of evolution and relaxation of the spins of the paired partners.

ROTATION INTRINSIC SPIN EFFECTS AND ITS ASTROPHYSICAL APPLICATION

On the basis of rotation-spin, torsion-spin and magnetic-spin effects, by which the spin precession arises the polarized magnetic field of neutron star to incline to the rotational axis. In the case of accretion layer structure of the recycled pulsar and the companion star magnetic influence considered, the magnetic inclinations of the recycled pulsars are different from that of the normal radio pulsars. The theoretical conclusions and consistent observational evidence is discussed.

Thermal expansion of chromium at high temperature.

Measurements of linear thermal expansion by pushrod dilatometry to 1873 K confirm the \ensuremath{\gamma}-ray density measurements by Stankus in 1993 which indicated that the coefficient of expansion of chromium increases much more rapidly above \ensuremath{\sim}1200 K than the heat capacity. The increase in expansion is also much greater than in Mo and W where anharmonicity is important. Magnetic spin effects are a possible source. \textcopyright{} 1996 The American Physical Society.

Interference of heavy-atom with magnetic spin effects in spin-correlated micellar radical pairs

The recombination kinetics of the radical pairs 3(SeH· .. An·+), with SeH+ = selenine, An = aniline, and 3(TH· .. An·+) with TH+ = thionine, p-Cl-An = 4-chloroaniline, in benzene/cetyldimethylbenzylammonium chloride/H2O reverse microemulsions was measured by ns-laser flash photolysis as a function of magnetic field and nanodroplet size. By comparison with the behaviour of the 3(TH· .. An·+) radical pairs evidence was provided that, besides the main route of triplet radical pair recombination through triplet to singlet spin conversion in situations when the radicals are separate and subsequent reaction on re-encountering as singlet radical pair, there is a finite probability that radical pairs encountering with overall triplet spin will directly recombine through electron transfer to singlet ground state products. The probability of this process, which is induced by spin-orbit coupling and is independent of a magnetic field, was evaluated for the three radical pairs specified above.

Magnetic-field-sensitive polymer composite materials

Polymer composite material, containing conducting filler particles (e.g. graphite) at concentrations above the percolation threshold should, as a conductor, exhibit certain magnetic-field-sensitive properties, such as the Hall effect or magnetoresistance. These effects not only allow them to be classified as smart materials, but also help in establishing the mechanism of conduction in such complex disordered systems. This paper reports the results of investigations on magnetoresistance in composite materials, prepared by direct polymerization of propylene on graphite particles. The method ensures grafting of polymer to the filler surface, imparting the properties to the composite. For composites with graphite, the magnetoresistance is positive for a filler volume fraction above the percolation threshold. Below the threshold the samples show weak negative magnetoresistance, characteristic of conduction through localized states in disordered systems. This result correlates with our model of double percolation over filler particles, surrounded by thin layers of injected charge. New magnetic effects have been found, such as oscillations of dark conductivity in magnetic field and resonance magnetic-spin effects.

Magnetic Spin Effects on Photooxidation Quantum Yields of RuII‐tris(bipyridine) Type Complexes in Magnetic Fields up to 17.5 Tesla

Spin‐control of the rate of electron transfer processes can also be detected in systems with very strong spin‐orbit coupling such as in the ruthenium complex [Ru(bpy)3]2+, bipy = 2, 2′‐bipyridine. From the influence of an external magnetic field, which was varied continuously up to the extremely high fields of 17.5 Tesla, the kinetic details of the very fast photooxidation of [Ru(bpy)3]2+ by methylviologen were determined quantitatively.

Magnetic spin effects as a tool for studying electronic processes in solids

AbstractThe role played by the law of the conservation of momentum in the primary processes of charge carrier generation is considered. External magnetic field is shown to be able to influence the rate constants governing spin dependent processes. Magnetic field effect and Reaction Yield Detected Magnetic Resonance on the photoconductivity of organic solids give important information on the mechanism of primary steps of charge photogeneration.

Magnetostatic field influence on electrodeposition on metal films

The relationship between the influence of a constant magnetic field with induction 0.05–0.19T and electrodeposition of copper, nickel and tin films with respect to electrochemical behaviour and mixed kinetics was found to exhibit an oscillating behaviour. A qualitative model is suggested which interprets the discovered relationship within the limits of the theory of magnetic spin effects. The model is based on the assumptions about the character of spin conversion of the system of three paramagnetic particles at chemisorption—an aquated ion, an adsorption centre, and an unpaired conduction electron.