The influence of the chemical magnetization of oceanic basalts on determining the geomagnetic field paleointensity by the Thellier method

Dredged samples of basalts from the Mid-Atlantic Ridge (MAR) and the Red Sea Rift that are 0.2 to 1 Ma in age are used to show the possibility of separating the thermoremanent and chemical remanent magnetization components in oceanic basalts by the conventional Thellier–Coe method. It is found that the decay rate of chemical remanent magnetization during exposure of basalt samples with Curie temperatures of T _c = 145 and 240°C at temperatures of 340–380°C in the air was less than the formation of partial thermoremanent magnetization during the experiments using the Thellier–Coe method by a factor of 4.5–5; in contrast, for thermoremanent magnetization these rates almost coincide. Using this fact, we estimated the contributions from chemical remanent and thermoremanent magnetization components into the natural magnetization of basalts and, based on the thermoremanent magnetization component, defined the paleointensity of the geomagnetic field for the epoch when these basalts formed. In basalts from the southern MAR that are 1 Ma in age, the contribution of chemical remanent magnetization to the natural remanent magnetization is 60% to 80%; in those of 0.35 Ma it was less than 50%; in those of 0.2 Ma it was less than 10%. The calculated values of the virtual magnetic dipole moment of the Earth were close to those that have been published in the literature.     

Comparative analysis of magnetic properties of the basalts collected in the Red Sea and other rift zones

The magnetic properties of basalts collected from the young rift zone of the Red Sea are studied in detail. Special features revealed in the magnetic behavior of the samples testify to a complex character of the evolution of the Red Sea rift zone. The magnetic characteristics of basalts from the Red Sea rift zone and other rift zones are compared. The reasons for high values of the natural remanent magnetization I _n and Königsberger factor Q _n obtained for the Red Sea basalts are clarified.     

A new class of surface magnetic TM polaritons in crystals with linear magnetoelectric effect

The conditions necessary for the formation of a new type of a surface magnetic TM polariton at the magnetic dielectric-nonmagnetic metal or the magnetic dielectric-nomagnetic dielectric interfaces are determined. The formation of a surface electromagnetic wave of this type is caused by the effect of spatial dispersion of a magnetic dielectric medium.     

The characterization of poorly chrystalline Si-containing natural iron oxides by Mössbauer spectroscopy

Soils developed from recent basalts of Marion Island in the Sub-Antarctic contain about 20% of a poorly crystalline iron oxide. The association of this phase with Al and Si appears to have a major influence on its Mössbauer spectra: whereas room-temperature spectra indicate a relatively regular structure, the magnetic hyperfine fields at 4.2K are lower than those of even the most poorly crystalline pure ferrihydrites.     

Formation of phase domain structures in thin films under conditions of a first-order magnetic phase transition

This paper reports on the results of a theoretical investigation into the magnetic and resonance properties of thin films in the range of the transition from a paramagnetic state to a ferromagnetic state in the case where the magnetic transition is a first-order phase transformation. It is demonstrated that, in an external magnetic field directed perpendicular to the film plane, the formation of a specific domain structure consisting of domains of the coexisting paramagnetic and ferromagnetic phases can appear to be energetically favorable. The parameters of the equilibrium system of stripe phase domains and their dependences on the temperature, the magnetic field, and the characteristics of the material are calculated. The specific features of the magnetic resonance spectra under the conditions of formed stripe phase domains are considered. A relationship is derived for the dependence of the resonance field of the system of ferromagnetic domains on the magnetization and temperature. It is shown that the alternating external field can fulfill an orientation function in the formation of stripe phase domains.     

A chronological test of ocean-bottom spreading in the North Atlantic

Fission-track and K-Ar dating of basaltic glass from the Mid-Atlantic Ridge gives results which are consistent with the proposal of ocean-floor spreading. Correlation exists between the magnetic anomaly patterns over the Crest Mountains at 45°N and the age of the outcropping basalts. The observed sequences of ages progressing outward from the Median Valley 11,000, 230,000, 310,000, 750.000, 8,000,000, and 16,000,000 years constitute strong, direct support for the idea of ocean-bottom spreading.     

Synthesis and magnetic states of cobalt in three-layer Co/Ge/Co films

The magnetic properties of three-layer Co-Ge magnetic films have been studied experimentally as a function of technological conditions of their deposition. It has been found that the films deposited at a high deposition rate have a granular structure, and the films obtained at a low deposition rate have an X-ray amorphous structure. Electron microscopy and nuclear magnetic resonance studies have demonstrated that, at the same cobalt layer thickness, the semiconductor granule sizes depend on the average semiconductor layer thickness and correlate with the formation of different cobalt phases (amorphous, cubic, and hexagonal). The thermomagnetic properties of the films have been investigated.     

Thermal electrodynamic mechanisms of a rise of current-voltage characteristic (IVC) of technical superconductors at magnetic flux creep

The processes of the formation of the macroscopic states of a superconducting tape induced by the transport current at magnetic flux creep have been studied. It has been shown that there are characteristic values of electric field intensity that are affected by a rate of current injection, properties of a superconductor, cooling conditions, and properties of a stabilizing matrix. These values are the basis of thermal electrodynamic mechanism, which determines the slope of a rise of IVC of technical superconductors. The conditions of formation of current instabilities have been studied taking into account a nonuniform temperature distribution over the cross section of a technical superconductor. The conditions of the existence of the IVC of technical superconductors have been formulated. These conditions allow for the stable heating of a superconductor as high as the critical temperature. The results of the carried out studies should be taken into account when measuring the IVC of superconducting materials and determining their critical parameters and the current of instability occurrence.     

Magnetic ordering in granular system

The conditions of the formation of different magnetic structures with ferromagnetic (FM) and antiferromagnetic (AFM) ordering in granular materials containing a subsystem of ferromagnetic granules are considered within the phenomenological approach. It is supposed that the magnetostatic field and the exchange interaction between conduction electrons and magnetic ions are responsible for the formation of magnetic structure.     

Multiple structure of two-pulse nuclear spin echo in cobalt films

The conditions for the formation of two-pulse echo signals from ⁵⁹Co nuclei in thin magnetic films at T=4.2 K are investigated. In the framework of the existing mechanisms, numerical simulation of the conditions for the formation of extra 3τ and 4τ echo signals (τ is the time delay between pulses) is carried out. It is shown that the multiple structure of the echo from ⁵⁹Co nuclei at T=4.2 K is due to a mechanism in which an additional hyperfine magnetic field proportional to nuclear magnetization is acting on the nuclear spin system.     

Local magnetic moments and hyperfine magnetic fields in Fe-M (M = Si, Sn) alloys at small metalloid concentrations

The main tendencies in the formation of local magnetic moments and hyperfine magnetic fields at Fe nuclei in Fe-Sn and Fe-Si alloys at low metalloid concentrations are analyzed on the basis of “first-principles” calculations. The results of calculations are compared with experimental data. The main differences between these alloys were proved to be due to the differences in their lattice parameters. It is shown that a significant contribution to the formation of the hyperfine field comes from the orbital magnetic moment and the Ruderman-Kittel-Kasuya-Yosida polarization, which depend on the impurity concentration and the distance to an impurity atom in the crystal lattice.     

The role of thermally activated processes in the formation of magnetosensitive point-defect complexes in NaCl: Eu single crystals

The formation of magnetosensitive point-defect complexes in NaCl: Eu crystals is investigated. It is shown that the formation of intermediate metastable magnetosensitive point-defect complexes and their subsequent spontaneous transformation into relaxation products are thermally activated processes and do not depend on the diffusion mobility of impurity-vacancy dipoles. It is revealed that the magnetic field induces a transition of the magnetosensitive point-defect complexes to a new state that cannot occur in the absence of a magnetic field. A variation in the heat treatment temperature makes it possible to enhance the magnetoplastic effect significantly (by a factor of three) and to create the appropriate conditions for the existence of magnetosensitive complexes in the crystal over a long period of time.     

Internal structure of magnetic endosomes

The internal structure of biological vesicles filled with magnetic nanoparticles is investigated using the following complementary analyses: electronic transmission microscopy, dynamic probing by magneto-optical birefringence and structural probing by Small Angle Neutron Scattering (SANS). These magnetic vesicles are magnetic endosomes obtained via a non-specific interaction between cells and anionic magnetic iron oxide nanoparticles. Thanks to a magnetic purification process, they are probed at two different stages of their formation within HeLa cells: (i) adsorption of nanoparticles onto the cellular membrane and (ii) their subsequent internalisation within endosomes. Differences in the microenvironment of the magnetic nanoparticles at those two different stages are highlighted here. The dynamics of magnetic nanoparticles adsorbed onto cellular membranes and confined within endosomes is respectively 3 and 5 orders of magnitude slower than for isolated magnetic nanoparticles in aqueous media. Interestingly, SANS experiments show that magnetic endosomes have an internal structure close to decorated vesicles, with magnetic nanoparticles locally decorating the endosome membrane, inside their inner-sphere. These results, important for future biomedical applications, suggest that multiple fusions of decorated vesicles are the biological processes underlying the endocytosis of that kind of nanometric materials.     

Magnetic resonance studies of three-layer FeNi/Bi/FeNi films

The interlayer coupling in three-layer FeNi/Bi/FeNi films is studied by electron magnetic resonance. The magnetic anisotropy at the permalloy–bismuth interface is shown to play a significant role in the formation of the magnetic state of the film structure. The interlayer coupling oscillation period is found to be about 8 nm. The interlayer coupling and the interface anisotropy and their temperature dependences are determined.     

First-principles study of single intrinsic vacancy formation and its effect on the electronic density states and magnetic moment of V-doped ZnO

We calculated the formation energy of single vacancy in V-doped ZnO in different conditions (oxygen or zinc rich) by first principles. Effect of an intrinsic vacancy on the electronic density of states and magnetic moment of V-doped ZnO (Zn₁₅VO₁₆) with and without single vacancy was also calculated. Our calculation was performed by the CASTEP program within spin-polarized GGA approximation implemented in materials studio software. The formation energy showed that oxygen vacancy inclined to stay far from vanadium (V) and zinc vacancy preferred to stay at a position near V. The calculated formation energy also showed that a zinc vacancy may automatically occur but an oxygen vacancy may not appear automatically. Vanadium doping introduced spin-polarization around Fermi level. For an energy favorable vacancy, an oxygen vacancy had little effect on the electronic density of states. A zinc vacancy made the spin-polarization peaks around Fermi level broaden and decreased their magnitude. For the magnetic moment in energy favorable configurations, an oxygen vacancy had little effect on the magnetic moment; a zinc vacancy significantly decreased the magnetic moment (as high as 63.7%). Changes in magnetic moments were consistent with electronic density of states. Our calculation may interpret various experimental magnetic moment values. Our work also provided a reference for preparing V-doped ZnO-based dilute magnetic semiconductors.     

Unexpected features in the magnetoresistance of a quantum well at room temperature

Well-resolved oscillations are reported in the resistivity of an InGaAs quantum well as a function of applied magnetic field below 1 Tesla. The oscillations are observed at room temperature and their magnetic field position depends on the component of the magnetic field in the plane of the well. Because of these unusual properties, the results cannot be due to bound states within the well but it is suggested that they can be explained by quantised states lying above the well in energy. The condition for the formation of the states is satisfied at lower magnetic fields than for normal Landau levels and the states are separated by larger energy intervals.     

Spatial distribution of magnetic field and persistent currents in Condon domain phase

The distributions of magnetic field above the surface of the sample due to existence of the diamagnetic domain structure are found. It is shown, that the constant magnetic induction splitting inside of a sample is caused by the magnetization current density, localised in the boundaries between adjacent domains, close to the sample surface. The properties of this current are studied. The influence of the domain wall thickness on the spatial distribution of magnetic field and magnetization current density is present. A possibility of detection of the changes in the magnetic field distribution in vacuum, close to the surface of the sample, by means of Hall probes, is discussed. The measurement of the spatial distribution of magnetic field can give lacking information about characteristic sizes of magnetic domain formation at the conditions of the strong de Haas van Alphen effect.     

Microstructures and magnetic properties of Fe---Pt permanent magnets

We have investigated the magnetic properties of Fe---38.5Pt, Fe---39.5Pt and Fe---50.0Pt (at%) alloys after various heat treatment conditions using a vibrating sample magnetometer, and correlated these properties with the microstructures of the alloys by transmission electron microscopy. The Fe---50Pt alloy shows poor magnetic hardness regardless of the heat treatment conditions. The magnetic hardness of the Fe---39.5Pt alloy shows a maximum value after annealing for 10 h at 873 K, while it monotonically decreases after annealing at 1073 K. The alloy with the highest coercivity was composed of a single phase γ₁ with an average domain size of approximately 10 nm. The electron diffraction results indicate that the alloy is frustrated with accumulated stress, induced by a cubic → tetragonal transformation which occurs without twinning. On the other hand, when stress is relieved by twin formation after prolonged aging, the coercivity decreases. By annealing at 1073 K, the well known polytwin structure evolves. However, only poor hard magnetic properties are observed when this polytwin structure appears. Hence, the highest coercivity is attributed to the formation of nanoscale L1₀ ordered antiphase domains which is expected to be a highly anisotropic single domain magnetic particle.     

Magnetic force microscopy of GaAs:Mn ferromagnetic semiconductors

The dependence of magnetic properties of GaAs:Mn and MnAs epitaxial films grown on GaAs (001) by laser ablation of Mn and undoped GaAs in a hydrogen atmosphere under the growth conditions has been studied by magnetic force microscopy (MFM). Magnetic probe calibration for quantitative MFM measurements was performed by scanning across the slit of the magnetic-head of a tape recorder through which controlled direct current was passed. The dipole approximation was used to describe the magnetic properties of the MFM probe. Nonuniformity of the magnetization of GaAs:Mn films related to the formation of MnAs nanoinclusions, which are ferromagnetic at 300 K, has been observed. The typical scales of the spatial nonuniformity of the magnetization of GaAs:Mn films were varied from 270 to 550 nm depending on the film-growth conditions. The MnAs phase was identified by MFM measurements at an elevated temperature (up to 80°N).     

Localized magnetic states in graphene

We examine the conditions necessary for the presence of localized magnetic moments on adatoms with inner shell electrons in graphene. We show that the low density of states at the Dirac point, and the anomalous broadening of the adatom electronic level, lead to the formation of magnetic moments for arbitrarily small local charging energy. As a result, we obtain an anomalous scaling of the boundary separating magnetic and nonmagnetic states. We show that, unlike any other material, the formation of magnetic moments can be controlled by an electric field effect.