High Frequency Magnetic Susceptibility Research Articles

Characteristics, sources, bio-accessibility, and health risks of organophosphate esters in urban surface dust, soil, and dustfall in the arid city of Urumqi in China

Sixty-eight paired samples of urban surface dust and soil as well as four samples of atmospheric dustfall were collected from the arid city of Urumqi in Northwest China. Thirteen organophosphate esters (OPEs) in these samples were analyzed for the characteristics, sources, bio-accessibility, and health risks of OPEs. The studied OPEs were widely detected in the urban surface dust, soil, and dustfall, with Σ13OPEs (total concentration of 13 OPEs) of 1362, 164.0, and 1367 ng/g, respectively, dominated by tris(2-chloroethyle) phosphate (TCEP), tri(2-chloroisopropyl) phosphate (TCiPP), tri(1, 3-dichloroisopropyl) phosphate (TDCiPP) and tris(2-butoxyethyl) phosphate (TBOEP), TBOEP and tri(2-ethylhexyl) phosphate (TEHP), and TCEP, TCiPP, TBOEP, triphenyl phosphate and TEHP, respectively. The low and high frequency magnetic susceptibility of surface dust and urban soil might indicate the pollution of OPEs in them. Elevated levels of the Σ13OPEs in the surface dust and urban soil were found in the west, south, and northeast of Urumqi city. The total deposition flux of dustfall-bound 13 OPEs ranged from 86.5 to 143 ng/m2/day, with a mean of 105 ng/m2/day. OPEs in the surface dust and urban soil were associated with the emissions of indoor and outdoor products containing OPEs, the dry and wet deposition of atmosphere, and the emissions of traffic. Trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tri-isobutyl phosphate, TCEP, TCiPP, TDCiPP, and TBOEP in surface dust and urban soil had relatively high bio-accessibility. The bio-accessibility of OPEs was mainly affected by the physio-chemical properties of OPEs. The non-cancer and cancer risks of human exposure to OPEs in surface dust and urban soil were relatively low or negligible. The current research results may provide scientific supports for prevention and control of pollution and risks of OPEs.

Tracing the origin of reservoir sediments using magnetic properties in Southeastern Brazil

Determining the origin of eroded soil is essential to design effective soil erosion control strategies which preserve the soil resource, enhance agricultural productivity, and reduce the negative impacts of soil erosion, in-field and off-field. Magnetic properties have been widely used in temperate environments to identify sediment sources, pathways and links, but there have been very few applications in tropical and subtropical environments. Therefore, in this paper we investigated reservoir sediment sources in the Upper Grande River Basin, Southeastern Brazil, using sediment tracing techniques based on magnetic parameters (low and high frequency magnetic susceptibility, frequency dependent susceptibility). The different parent materials and subtropical weathering conditions resulted in soils having different Fe oxide minerals and Fe oxide contents, promoting magnetic variability that allowed comparison and identification of possible sources of reservoir sediments in order to reduce water erosion impacts. The results indicate the suitability of magnetic properties as a tracer for soil erosion studies in tropical environments.

Identification of magnetic minerals in the peatlands cores from Lake Diatas West Sumatra, Indonesia

Peatlands in Lake Diatas can store various types of minerals. One of the mineral phases that can be found in peatlands are magnetic minerals derived from volcanic eruptions. This study was used to determine concentration of magnetic minerals found in peatlands. We applied the rock magnetism method, measuring the magnetic susceptibility of peat sediments to estimate the concentration of magnetic minerals within a peat core. Bartington Magnetic Susceptibility Meter type MS2C and dual frequency MS2B types, namely 470 Hz and 4.7 k Hz. In this study we analysed the magnetic susceptibility of core Diatas REP B at depths of 0-170 m and 240-720 m. From MS2B the values of low frequency magnetic susceptibility (χif )and high frequency magnetic susceptibility (χhf ) are obtained. The magnetic susceptibility values ranged from 365,2 × 10−8 m3/kg to 386,8 × 10−8 m3/kg and the value of magnetic susceptibility depends on frequency (%χfds ) range between 0,6 % - 1,3%. These low values indicate that almost no superparamagnetic grains are present. We identified a positive peak in magnetic susceptibility 386,8 × 10−8 m3/kg at 693 cm, whereas the lowest values were messured 365,2 × 10−8 m3/kg at 675 cm. Based on the value of magnetic susceptibility, the dominant magnetic mineral phases are Hematite (Fe2O3) and ilmenite (FeTiO3).

Numerical calculation of high frequency magnetic susceptibility in thin nanocrystalline magnetic films

Two numerical micromagnetic methods most suitable for calculation of the high frequency magnetic susceptibility of nanocrystalline thin films were considered in detail. The methods are based on the Landau–Lifshitz equation, linearized around the equilibrium state leading to an eigenvalue problem or solved using an undetermined coefficients technique. An analysis and estimation of an efficiency of the methods were carried out. Several conclusions about their advantages and shortcomings, as well as specifics of their practical application were drawn.

Increased ultra high frequency magnetic susceptibility in nanopatterned nanolayers with strong exchange coupling

In this work, we report the magnetic properties of a set of magnetic multilayers whose particular nanostructure allows control of their in-plane, uniaxial magnetic anisotropy value and consequently the magnetic susceptibility measured at ultra high frequencies. Particularly, two sets of samples with the compositions ((Co15 nm-54°) (Cox nm-0°) (Ta6 nm-54°))n and ((Fe10 nm-54°) (Fex nm-0°) (Ta6 nm-54°))n where n is the number of trilayers. In every sample, the obliquely and normally deposited ferromagnetic layers were strongly exchange-coupled. Consequently, the value of the uniaxial in-plane magnetic anisotropy could be controlled by changing the thickness of the normally deposited layer (x). Subsequently, the magnetic susceptibility of the samples could be tailored. Thus, the ferromagnetic resonance frequency value may be controlled and increased to up to 6.3 GHz for the samples with larger magnetic anisotropy values.

Brownian motion and quantum dynamics of magnetic monopoles in spin ice

Spin ice illustrates many unusual magnetic properties, including zero point entropy, emergent monopoles and a quasi liquid–gas transition. To reveal the quantum spin dynamics that underpin these phenomena is an experimental challenge. Here we show how crucial information is contained in the frequency dependence of the magnetic susceptibility and in its high frequency or adiabatic limit. The typical response of Dy2Ti2O7 spin ice indicates that monopole diffusion is Brownian but is underpinned by spin tunnelling and is influenced by collective monopole interactions. The adiabatic response reveals evidence of driven monopole plasma oscillations in weak applied field, and unconventional critical behaviour in strong applied field. Our results clarify the origin of the relatively high frequency response in spin ice. They disclose unexpected physics and establish adiabatic susceptibility as a revealing characteristic of exotic spin systems.

Cylindrical magnetization model for glass-coated microwires with circumferential anisotropy: Dynamics

The high frequency magnetic susceptibility of glass-coated microwires with effective circumferential anisotropy has been modeled by micromagnetics. In their amorphous and magnetically soft metallic nucleus, the negative magnetostriction induces a continuous and non-uniform vortex-like structure, with an axially magnetized core coupled to a circumferentially magnetized outer shell. The model is a one-dimensional radial micromagnetic model where exchange, magnetoelastic and magnetostatic energies are considered. The microwave permeability under AC (axial and circumferential) fields is found to be expressed as a sum over a set of eigenmodes, each with a characteristic resonance frequency. In the framework of this model, a sum rule on the frequency-dependent permeability is shown to hold. It provides a figure of merit and guidelines for the design of high permeability materials for applications in the microwave range.

Effect of the Correlation Properties of One- and Three-Dimensional Inhomogeneities on the High-Frequency Magnetic Susceptibility of Sinusoidal Superlattices

The effect of one-(1D) and three-dimensional (3D) inhomogeneities on the high-frequency magnetic susceptibility at the boundary of the first Brillouin zone of a ferromagnetic superlattice is studied. The study is performed with an earlier developed method of random spatial modulation (RSM) of the superlattice period. In this method, structural inhomogeneities are described in terms of the random-phase model, in which the phase depends on three coordinates in the general case. The frequency spacing Δνm between two peaks in the imaginary part of the averaged Green’s function, which characterizes the gap width in the frequency spectrum at the boundary of the Brillouin zone, is calculated as a function of both the root-mean-square fluctuations γi and the correlation wavenumbers ηi of phase inhomogeneities (i = 1 and 3 for 1D and 3D inhomogeneities, respectively). The function Δνm(γ1, η1) for 1D inhomogeneities is shown to be symmetric with respect to interchanging the variables γ 1 2 and η1, whereas the function Δνm(γ3, η3) for 3D inhomogeneities is strongly asymmetric with respect to interchanging γ 2 3 and η3. This effect is associated with the difference in form between the correlation functions of 1D and 3D inhomogeneities and can be used to determine the dimensionality of inhomogeneities from the results of spectral studies of such superlattices.

Critical relaxation spectra in EuS above T0

Using a bridge method, we have measured the high frequency magnetic susceptibility of EuS in the critical region and obtained its critical relaxation spectra. The appearance of double peaks in the frequency dependence curve of χ″ has been found for the first time.

Critical Behaviour of Spin Relaxation in EuS

We have measured both real and imaginary part of magnetic susceptibility of EuS near the Curie temperature T c by means of the high frequency magnetic susceptibility measurement method, in which no demagnetization corrections have been required. Except for the immediate vicinity of T c , the critical relaxation spectra obtained are described by a Debye form of relaxation and the critical index of the relaxation time is determined to be Δ =1.26±0.03. The value of Δ is slightly smaller than that of the static susceptibility, γ=1.41±0.01. For temperatures closer to T c , the critical relaxation spectra become to exhibit a polydispersive character.

Critical Relaxation Studied by High Frequency Magnetic Susceptibility in Mn(COOCH3)2·4H2O

The critical relaxation of the uniform mode in Mn(COOCH 3 ) 2 ·4H 2 O near the phase transition point was studied by using the high frequency susceptibility technique (up to 450 MHz). A dip was found in χ'(ω) just at T N in the frequency range higher than 180 MHz. This is a clear evidence of the critical slowing down. The dispersion is found to be monodispersive except the immediate vicinity of the transition point, where it changes to slightly polydispersive. The relaxation time is expressed as τ∝ e - Δ , Δ =1.30±0.03 for \(3\times10^{-2}{\lesssim}\varepsilon{\lesssim}1\) ( e =|1- T / T N |). The exponent Δ is smaller than that of the static susceptibility, γ=1.53±0.03 for \(6\times10^{-2}{\lesssim}\varepsilon{\lesssim}1\).

Critical Divergence of the HF Magnetic Susceptibility of SmFeO3 in the Spin Reorientation Temperature Region

The high frequency magnetic susceptibility of SmFeO 3 was measured near the spin reorientation temperature region and the instability of the spin system was observed as the divergence of the susceptibility at the onset and the end temperatures of the spin reorientation. The critical index of the susceptibility was found to be nearly equal to 1, which was discussed using a phenomenological expression of the free energy.

The Dynamical Magnetic Characters of R0.3Y2.7IG and R0.3Gd2.7IG Studied by Spin Echo and High Frequency Magnetic Susceptibility Measurements

In order to obtain information about the low magnetic loss ions of the rare earths (R) the spin echo investigations and the high frequency magnetic susceptibility measurements in (R-Y) IG and (R-Gd)IG systems have been performed at room temperature. It is established clearly that the spin echo method is useful in selecting the low magnetic loss rare earth ions, and that the wall motion is considerably affected by the difference in the lattice parameters between the solute (RIG) and the solvent materials (YIG and GdIG). The rare earths in (R-Y)IG which have little bad effect on the dynamical characteristics of the domain wall, are found to be La, Pr, Nd, Sm and Gd among the light rare earths or Yb, Tm and Lu among the heavy ones.

The Nonlinear Magnetic Susceptibility of YIG in the High Frequency Magnetic Field near the Curie Temperature

In order to obtain the information about nonlinear terms of the high frequency magnetic susceptibility at 2MHz near the Curie temperature the 2nd and 3rd order nonlinear terms against the high frequency magnetic field are derived from the observations of the 2nd and 3rd harmonics. Both terms decrease abruptly as the temperature deviates from the Curie temperature. It is a very remarkable result that the 2nd harmonic signal is observed above the Curie temperature in contradiction to the simple theoretical consideration. As for the 3rd harmonic its temperature dependence is explained qualitatively by the molecular field theory.

Spin Relaxation on Yttrium Iron Garnet near Curie Temperature Studied by High Frequency Magnetic Susceptibility

The high frequency magnetic susceptibilities in yttrium iron garnet are observed in the temperature range from 546 K and 553 K in the high frequency range from 100 kHz to 100 MHz and the low frequency range lower than 100 Hz. The anomalous sharp peak appears in the temperature dependence curves of the imaginary part of the magnetic susceptibility in MHz range and is broadened with increasing frequency. From frequency dependence of the magnetic susceptibilities it is made clear that the relaxation of spin system occurs in the above two frequency ranges and relaxation process near the Curie temperature is not monodispersive but polydispersive. The temperature dependence of the relaxation time in spin system is obtained near the Curie temperature and is corresponding with the critical slowing down phenomena.

Paramagnetic Resonance Absorption in Salts of the Iron Group

When a paramagnetic salt is placed in a high frequency alternating magnetic field which is perpendicular to a static magnetic field, energy may be absorbed by the salt in a resonant fashion for a range of values of the steady field. These paramagnetic losses have been investigated for three manganous, two cupric, and one chromic salt at a frequency of 9375 mc/sec. Well-defined absorption maxima were obtained in all cases, and absolute values of ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}$, the imaginary part of the high frequency magnetic susceptibility, are presented.