Resonance magnetoplasticity in the EPR scheme under ultralow magnetic fields

Resonance relaxation displacements of dislocations in NaCl crystals exposed to crossed ultralow magnetic fields (static field B = 26–261 μT and radiofrequency field B ～ 3 μT) in the electron paramagnetic resonance scheme are studied. The effect is also observed in the magnetic field of the Earth when crossed with a pulsed pump field with a resonance duration of ～0.5 μs. Changes in the microhardness of crystals of ZnO, triglycine sulfate, and potassium hydrogen phthalate after their exposure to the magnetic field of the Earth and the orthogonally directed pump field are found out.     

Hyperfine interactions and electronic structures of BaFe 2 As 2 : a first-principles LDA+U study

The hyperfine parameters of hyperfine fields, electric field gradients and isomer shifts at the Fe site are investigated based on the first-principles calculations of the electronic structures using LDA (GGA)+U method in the low-temperature orthorhombic antiferromagnetic phase of undoped BaFe₂As₂. It is fond that the electric field gradient of Fe nucleus is highly related with the electronic structures close to the Fermi level. Though the addition of negative on-site Coulomb interaction to Fe-3d states improves the calculated magnetic moment of Fe atom and the hyperfine parameters of Fe nucleus when U = ?0.1 Ry (?0.08 Ry) for GGA+U (LDA+U) method, a negative U correction does not capture the right physics of this system. The calculations prove the strong coupling between the magnetic, structural and electronic properties in antiferromagnetic BaFe₂As₂ parent.     

Vacancy induced magnetism in SrTiO3

Vacancy-induced magnetism in perovskite SrTiO₃ is investigated by ab initio calculations and magnetic measurements. The calculations of the generalized gradient approximation (GGA), the local density approximation (LDA) and the local density approximation with on-site effect U (LDA+U) methods show that stoichiometric SrTiO₃ is nonmagnetic. The GGA calculated results indicate that Ti or O vacancy could induce magnetism rather than Sr vacancy. The LDA and LDA+U calculations show that the Ti vacancy could induce magnetism, while Sr and O vacancies couldn't. The experimental results confirm that SrTiO₃ nanocrystalline powders exhibit room-temperature ferromagnetism (FM) and the magnetic moment results from cation vacancies.     

Correlation between hydrogen/deuterium exchange and Amide I band intensity in hemoglobin aqueous solution under static or 50 Hz magnetic field

Samples of hemoglobin in deuterium oxide solution (D₂O) and in bidistilled H₂O water solution, both at the concentration of 100 mg/ml, were exposed to a static magnetic field at 100 mT; analogous samples were exposed to 50 Hz magnetic field at 1 mT. Fourier Transform Infrared (FTIR) Spectroscopy was used to analyze separately the response of the secondary structure of this protein (diluted in both aqueous solutions) to separated exposure to both magnetic fields. The most relevant result which was observed after exposures was the significant increasing in intensity of the Amide I band, which was already explained in previous studies assuming that proteins α-helix aligned along the direction of the applied magnetic field due to its large dipole moment. In particular, in this study it was shown that hydrogen/deuterium exchange induced a reduction of the increasing of Amide I vibration band. This result can be explained assuming that Amide hydrogens of hemoglobin exchange with solvent deuterium atoms, causing an increase in mass of the protein and a correlated increasing in inertia of the α-helix, reducing significantly the torque effect of the applied magnetic field.     

Modeling of two-phase magnetic materials based on Jiles-Atherton theory of hysteresis

The Jiles-Atherton (JA) theory of hysteresis has been extended in the present paper to model hysteresis in two-phase magnetic materials. Two-phase materials are those that exhibit two magnetic phases in one hysteresis cycle: one at lower fields and the other at higher fields. In magnetic hysteresis, the transition from one phase to the other i.e. low field phase to high field phase depends mainly on the exchange field. Hence, the material-dependent microstructural parameters of JA theory: spontaneous magnetization, M_S, pinning factor, k, domain density, a, domain coupling, α, and reversibility factor, c, are represented as functions of the exchange field. Several cases based on this model have been discussed and compared with the measured data from existing literature. The shapes of the calculated and measured hysteresis loops are in excellent agreement.     

Effects of in utero exposure to 4.7 T MR imaging conditions on fetal growth and testicular development in the mouse

The effects of exposure in utero to high field (4.7 T) magnetic resonance imaging (MRI) conditions on fetal growth, adult growth, and testicular development in the mouse were investigated. Exposures of 8-h duration were made on day 9 and/or day 12 of gestation. Also investigated were effects of a combined treatment regime using continuous wave, unfocussed 1 MHz ultrasound on day 9 and MRI on day 12. Treatment groups consisted of 8 to 10 pregnant dams. Fetal data were taken on day 18 of gestation and data from adult animals that were exposed in utero were taken on day 50 postpartum. Significant differences in sensitive biological end points following in utero exposure to complex MRI field conditions were found. Fetal weights of the exposed groups ranged from 11% (day 9 MRI) to 17% (day 9 ultrasound/day 12 MRI) lower (p ≤ .05) than those of the cage control and sham-exposed fetuses and crown-rump length of exposed animals was reduced by 8% (p ≤ .05). The postpartum death rate was as high as 38% (significant at p ≤ .05 level) following MRI exposure on day 9 and day 12 of gestation. Daily sperm production was reduced by as much as 44% (p ≤ .05) in adults exposed to MRI on day 12 of gestation. A reduction in testis weight and volume in the adult males was also seen, but the difference was not statistically significant at the p ≤ .05 level. No effect was seen on embryonic deaths, sex ration, body weight at day 50, spleen weight, or seminal vesicle weight. The mechanism responsible for these results could involve one or more of the applied fields interacting with a sensitive stage of fetal development. Further studies are planned to isolate the individual field components and to elucidate biochemical and/or hormonal changes that may follow in utero exposure.     

Viscous flow of magnetic vortices and rapid relaxation of magnetization in YBaCuO ceramics

The viscous flow of magnetic vortices in granular YBaCuO ceramics of various granule sizes is investigated using the microwave absorption method (f=80 MHz) in the range of varying magnetic fields H=±1500 Oe and of temperatures T=77 to 95 K. The conditions for the formation and melting of the vortex lattice, as well as the transition of the high-temperature superconductor (HTSC) state from the irreversibility region to the region of the viscous flow of magnetic vortices, are considered. The rapid magnetic relaxation times in the range τ=72 to 111 ms are determined from the magnetization relaxation in the HTSC materials under investigation depending on the granule size d, which varies from 1 to 30 μm. The experimental results on the variation of the relaxation time τ from 77 to 120 ms in a ceramic exposed to fast neutrons with various fluences (Φ=10¹⁶ to 10¹⁹ cm⁻²) are considered. The depinning process is analyzed; it occurs in the form of a thermally assisted flux flow in the range of low activation energies. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 6, 2001, pp. 968–973. Original Russian Text Copyright ? 2001 by Chashchin.     

On the relationship between the lightning electromagnetic field and the channel-base current based on the TL model

A set of approximation expressions relating the lightning channel-base current and the lightning electric and magnetic fields on earth surface are proposed respectively in the near-zone and far-zone, by employing the transmission line (TL) model. The derived expressions show that, the electric and magnetic fields waveforms can be expressed approximately by the channel-base current waveform with different factors at a certain distances, whether in the near-zone or far-zone. The factors can be expressed in terms of the return stroke wavefront speed v, the speed of light c, and the horizontal distance r between the return-stroke channel and the observation point.     

Magnetic properties of Li<Subscript>2</Subscript>RuO<Subscript>3</Subscript> as studied by NMR and LDA + DMFT calculations

We present results of the combined study of the magnetic properties of Li₂RuO₃ by means of nuclear magnetic resonance (NMR) spectroscopy and theoretical dynamical mean-field theory (LDA + DMFT) calculations. The NMR data clearly show the onset of a thermal activation process in the high temperature region, T > 560K, which is tentatively ascribed to the formation of the valence bond liquid. The LDA + DMFT calculations demonstrate that the magnetic response at these temperatures is mostly due to the xz/yz orbitals, while the xy orbitals of Ru still form molecular orbitals. Thus, Ru ions are in the orbital-selective state in the high temperature phase of Li₂RuO₃.     

Elastic properties and phonon dispersions of rhenium in hexagonal-close-packed structure under pressure from first principles

The elastic properties of the hexagonal-close-packed (hcp) structure rhenium (Re) and their behavior under pressure are investigated using the local density approximation (LDA) and the generalized gradient approximation (GGA). The obtained high pressure elastic constants are well consistent with previous theoretical date, while large discrepancies are found between theory and the high pressure experiments. The calculated isothermal bulk modulus B₀ (376 GPa for GGA and 389 GPa for LDA) and its initial pressure derivative (4.52 for LDA and 4.58 for GGA) compare favorably with the experimental values. Moreover, it is found that the value of c/a, B/G, Poisson's ratio, and B_c/B_a are virtually independent of pressure. We also performed calculation for phonon dispersions at high pressure. GGA in our calculation exhibits a same trend as the high pressure experimental curve.     

In vivo boron-11 MRI and MRS using (B24H22S2) in the rat

In vivo boron-11 magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) were performed on a rat that had been infused with a potential boron neutron capture therapy agent, Na₄B₂₄H₂₂S₂, using methods for detecting nuclei with a short T₂ relaxation time. MRI and MRS were also performed on a euthanized rat that had been similarly infused in vivo. Boron-11 spectral intensities decreased in the living rat over a 25-h period. The results demonstrate the capability of MRI and MRS to noninvasively monitor the distribution and excretion of boron agents in vivo.     

Local Magnetic Fields in Some Bismuth-Based Diamagnets

Evidence that local ordered magnetic fields from 30 to 250 G exist in bismuth-based diamagnetic compounds comprising neither d- nor f-elements was given by ²⁰⁹Bi NQR spectroscopy and supported by SQUID measurements of α-Bi₂O₃. The NQR experiments involved a study of the zero-field line shapes, analysis of the Zeeman-perturbed patterns, and examination of the zero-field spin-echo envelopes in single crystals and powders. The results of the experiments followed by computer modeling of the observed spectra were interpreted assuming that ordered magnetic fields are located at the bismuth sites in α-Bi₂O₃, Bi₃O₄Br, Bi₂Al₄O₉, Bi₄Ge₃O₁₂, Bi₂Ge₃O₉ and perhaps in Bi₃B₅O₁₂. A survey of the related ²⁰⁹Bi NQR data is here presented.     

Magnetic properties of NdSb,GdSb, TbSb,DySb, HbSb and ErSb under hydrostatic pressure

The hydrostatic pressure dependence of magnetic properties are reported for antiferromagnetic RSb where R = Nd, Gd, Tb, Dy, HoorEr. Measurements were made for pressures 0 ≤ p ≤ 10 kbar, magnetic fields 0 ≤ H₀ ≤ 60 kG, and temperatures 1.4 K ≤ T ≤ 35 K. dT_N/dP shows no systematic trend and ranges from -0.038 K/kbar for DySb to + 0.21 K/kbar for NdSb. The magnetic properties of DySb are strongly P-dependent, whereas those of HoSb are P-independent, but sample-dependent.     

Stability of ferrimagnetic multilayers

We study the field induced instability of the ground state of ferrimagnetic multilayers consisting of a stacking alternating two different uniaxial ferromagnetic layers. For multilayers with even number of layers N, we obtain analytical expressions for the critical fields in terms of the magnetic parameters (anisotropies, and interlayer exchange coupling), for any value of N. The critical fields are calculated from the energy fluctuations for small variations in the equilibrium magnetic profile. The form of the hysteresis curves is discussed, using the expressions of the critical fields.     

Properties of exchange interaction in Yb3Fe5O12 under extreme conditions

In Yb₃Fe₅O₁₂, the exchange effective field can be expressed as H_eff=−λ·M_Fe=−λχ_eff·H_e=−γ·H_e where γ is named as the exchange field parameter and H_e is the external magnetic field. Then, in this paper, by the discussions on the characteristics of the exchange field parameter γ, the properties of exchange interaction in ytterbium iron garnet (Yb₃Fe₅O₁₂) are analyzed under extreme conditions (high magnetic fields and low temperatures). Our theory suggests that the exchange field parameter γ is the function of the temperatures under different external magnetic fields, and γ=a+b·T+c·T², where the coefficients a, b, c are associated with the external magnetic fields and the magnetized directions. Thus, the temperature-dependence, field-dependence and anisotropic characteristics of the exchange interaction in Yb₃Fe₅O₁₂ are revealed. Also, excellent fits to the available experiments are obtained.     

Mössbauer characterization of Nd0.7Sr0.3(Mn1−x57Fex)O3 (x=0.02–0.15)

The magnetic structure of colossal magneto-resistive Nd_0.7Sr_0.3(Mn_1−x⁵⁷Fe_x)O₃ (x=0.02, 0.05, 0.10, and 0.15) has been studied by Mössbauer spectroscopy in magnetic fields up to 60 kG. ⁵⁷Fe ions appear to spread over two different magnetic phases. One of them remains ferromagnetic for all values of x, but the other one changes from canted to anti-ferromagnetic with increasing x. For x=0.02 and 0.05, the latter magnetic phase is comprised of small clusters, which are very sensitive temperature and strongly influenced by the applied fields.     

Mössbauer and magnetometric studies of the magnetism of quasi-ordered Fe-Al alloys with Ga, V and Mn admixtures

The introduction of additives of Ga, V and Mn (M _x,y = 0, 5, 10 at %) to ordered alloys Fe₆₅Al₃₅-Fe_{65 ? y} Al_{35 ? x} M _x,y is aimed at studying the general and specific features of the magnetic characteristics of these alloys as functions of their temperatures (5–300 K) and magnetic fields (up to 5 T). In this work, we discuss the possibiliy of interpreting the combined results from magnetometry and Mössbauer spectroscopy in terms of magnetic phase separation and models of localized magnetic moments.     

Giant volume magnetostriction and colossal magnetoresistance in La0.7Ba0.3MnO3 at room temperature

In single-crystal La_0.7Ba_0.3MnO₃, giant volume magnetostriction was observed for the first time to reach 2.54 × 10^?4 at room temperature and a still larger level of 4 × 10^?4 at the Curie point T _C = 310 K in a magnetic field of 8.2 kOe. At the same temperatures and magnetic field, this effect is complemented by a colossal magnetoresistance of 15.2 and 22.7%, respectively. The volume magnetostriction ω and magnetoresistance Δρ/ρ follow similar patterns in the proximity of T _C; namely, ω and Δρ/ρ are negative, maxima are observed in the |ω|(T) and |Δρ/ρ|(T) curves, and the ω and Δρ/ρ isotherms do not saturate in the highest fields applied. These phenomena are assigned to the fact that, in the above composition, there exists a two-phase magnetic (ferromagnetic-antiferromagnetic) state induced by strong s–d exchange.     

Critical wall perturbations and a local free energy functional

On the basis of an ad hoc local free energy postulate recently advanced by de Gennes and Fisher, predictions are made for the local composition/magnetization perturbations induced near a wall by the presence of a second parallel wall at finite separation D, in a system at its bulk critical point. Despite some apparently serious limitations of the postulate, which are exposed, the most striking predictions for the behavior at large D are confirmed by new, exact calculations for the free energy of an n × ∞ spin $\text{1}\text{2}$ Ising model strip with distinct surface magnetic fields, H₁ and H_n, imposed on opposite boundaries.     

Redistribution of electrons between ellipsoids in a magnetic field in the quantum limit range in n-Bi-Sb alloys

The magnetoresistivities ρ₂₂(H) and ρ₃₂(H) and the Hall coefficient R _32.1 for single-crystal samples of the n-Bi_0.93Sb_0.07 semiconducting alloy have been measured at low temperatures in magnetic fields up to H=14 T at H∥C ₂. The samples with three electron concentrations n ₁=1.25 × 10¹⁶ cm^s-3, n ₂=3.5×10¹⁶ cm^s-3, and n ₃=1.6×10¹⁷ cm^s-3 have been studied. The strong anisotropy of the electron spectrum of the alloys has made it possible to observe quantum oscillations of the magnetoresistivity ρ₂₂ (H) at H∥C ₂ for electrons of the secondary ellipsoids with the transition to the quantum limit in high magnetic fields. However, in the same magnetic fields, the quantization condition for electrons of the main ellipsoid is not satisfied. An increase in the energy of electrons of the secondary ellipsoids in the magnetic fields of the quantum limit leads to their migration to the main ellipsoid. After the complete migration, the Fermi energy for the alloy samples with the electron concentrations n ₁, n ₂, and n ₃ increases from 7.0 to 11.3 meV, from 11.0 to 17.1 meV, and from 20.2 to 30.6 meV, respectively. After the migration, the magnetoresistivity for electrons of the main ellipsoid increases with an increase in the magnetic field and the specific features in the behavior of the kinetic coefficients are observed in the vicinity of the magnetic field H=10 T. Therefore, the electronic topological transition from the three-valley electron spectrum to the single-valley electron spectrum occurs in the Bi_0.93Sb_0.07 single crystals for H∥C ₂ at low temperatures in the range of magnetic fields of the quantum limit.