Spectral ellipsometry studies of the optical functions, first observation of photoluminescence and low frequency dielectric permittivity investigations were performed in ferroelectric - multiferroic TbMnO3 single crystals. The main attention was paid to electronic band structure, nature of the main optical transitions and unusual behavior of the dielectric permittivity in the region of the sharp narrow temperature maximum, associated with ferroelectric phase transition. It was found that magnitude of the permittivity maximum decreases strongly with frequency, whereas position of maximum is frequency independent. Observed features of polarization response can be described satisfactorily in the frame of on the basis of the Landau-Khalatnikov theory for critical relaxation polarization
The intercalated water into nanopores exhibits anomalous properties such as ultralow dielectric constant.~Multi-scale modeling and simulations are used to investigate the dielectric properties of various crystalline two-dimensional ices and bulk ices. Although, the structural properties of two-dimensional (2D-) ices have been extensively studied, much less is known about their electronic and optical properties. First, by using density functional theory (DFT) and density functional perturbation theory (DFPT), we calculate the key electronic, optical and dielectric properties of 2D-ices. Perform…
The authors of the title paper report to have grown ammonium hydrogen L-tartrate (1) by use of L-glutamine and L-tartaric acid in 1:1 mole ratio. Many points of criticism pertaining to the characterization of 1 are described herein.
Three types of BaTiO3 core - amorphous nano-shell composite ceramics were processed from the same core-shell powder by standard sintering, spark-plasma sintering and two-step sintering techniques and characterized by XRD, HRSEM and broad-band dielectric spectroscopy in the frequency range 10^3 - 10^13 Hz including the THz and IR range. The samples differed by porosity and by the amount of interdiffusion from the cores to shells, in correlation with their increasing porosity. The dielectric spectra were also calculated using suitable models based on effective medium approximation. The measureme…
Poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonic acid (PEDOT:PSS), an optically transparent organic semi-conductor, constitutes a suspension of conducting PEDOT:PSS grains, shelled by an insulating layer of PSS. While a percolation network enhances dc conductivity, structural and electrical inhomogenity hinters electric charge flow giving rise to capacitance effects. In the present work, two distinct relaxation mechanisms are detected by Broadband Dielectric Spectroscopy (BDS). Double polarization mechamisms are predicted by bi-phase suspension dielectric theory. Within the frame of in…
Using first-principles density functional calculations, we study the electronic and magnetic properties of ferromagnetic insulating double-perovskite compound La2NiMnO6, which has been reported to exhibit interesting magnetic field sensitive dielectric anomaly as a function of temperature. Our study reveals existence of very soft infra-red active phonons that couple strongly with spins at the Ni and Mn sites through modification of the super-exchange interaction. We suggest that these modes are the origin for observed dielectric anomaly in La2NiMnO6.
The solid solution 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) is a promising lead-free piezoelectric material with exceptionally high piezoelectric coefficients. The strong response is related to structural instabilities close to ambient temperature. We report here on temperature-induced anomalies in the dielectric, piezoelectric, and elastic coefficients and Raman spectroscopy of ceramic BCZT. The data indicate ferroelectric-ferroelectric structural phase transitions in this material in addition to those previously reported. An anomaly is also observed above the Curie temperature TC and i…
Polycrystalline M-type hexagonal Strontium hexaferrite and its modified systems by Cobalt (Co) and Titanium (Ti) were successfully prepared by the solid state reaction method. The single phase formation of all the systems and well grain growth of micrometer range was confirmed by X-ray diffraction pattern and Scanning Electron Microscopic image respectively. The impedance spectroscopy and dielectric properties were investigated in a selected frequency & temperature range. The room temperature M-H loop study for Strontium hexaferrite and Cobalt modified Strontium hexaferrite was carried out by …
We discuss a non-perturbative, technically straightforward, easy-to-use, and computationally affordable method, based on polarization theory, for the calculation of the electronic dielectric constant of insulating solids at the first principles level. We apply the method to GaAs, AlAs, InN, SiC, ZnO, GaN, AlN, BeO, LiF, PbTiO$_3$, and CaTiO$_3$. The predicted $\einf$'s agree well with those given by Density Functional Perturbation Theory (the reference theoretical treatment), and they are generally within less than 10 % of experiment.
We present a local representation of the electronic dielectric response function, based on a spatial partition of the dielectric response into contributions from each Wannier function using a generalized density functional perturbation theory. This procedure is fully ab initio, and therefore allows us to rigorously define local metrics, such as "bond polarizability," on Wannier centers. We show that the locality of the response function is determined by the locality of three quantities: Wannier functions of the occupied manifold, the density matrix, and the Hamiltonian matrix. In systems with …
The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO$_2$) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO$_2$, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-H…
Graphene field-effect transistors are integrated with solution-processed multilayer hybrid organic-inorganic self-assembled nanodielectrics (SANDs). The resulting devices exhibit low-operating voltage (2 V), negligible hysteresis, current saturation with intrinsic gain > 1.0 in vacuum (pressure < 2 x 10-5 Torr), and overall improved performance compared to control devices on conventional SiO2 gate dielectrics. Statistical analysis of the field-effect mobility and residual carrier concentration demonstrate high spatial uniformity of the dielectric interfacial properties and graphene transistor …
Recently it has been demonstrated that a careful treatment of both longitudinal and transverse matrix elements in electron energy loss spectra can explain the mystery of relativistic effects on the {\it magic angle}. Here we show that there is an additional correction of order $(Zα)^2$ where $Z$ is the atomic number and $α$ the fine structure constant, which is not necessarily small for heavy elements. Moreover, we suggest that macroscopic electrodynamic effects can give further corrections which can break the sample-independence of the magic angle.
Band gap tuning and dielectric properties of small organic ligands adsorbed on tin monolayers (stanene) have been investigated using first-principles calculations. Charge density analysis using density-functional theory shows that the ligands are chemisorbed on stanene and some of the groups can open a band gap in the originally metallic statene. Furthermore many-body GW calculations demonstrate that the dielectric properties of bare and ligand adsorbed stanene have a large anisotropy. Our findings of a finite gap opens a path for rational theoretical design of functionalized two-dimensional s…
Representation of dielectric properties by impedance spectroscopy (IS) is analyzed carefully in this paper. It is found that IS is not a good tool to describe a uniform system because a pseudo relaxation peaks exists at low frequency limit corresponding to direct current (DC) conductivity and two relaxation peaks appears simultaneously corresponding to one relaxation process for a high loss system with tand>1. However it is very convenient to describe a multiple phase system with IS. When dielectric properties are shown by Cole-Cole equation, only one Cole-Cole arc appears for one phase in IS,…
Dynamics of the main dielectric anomaly in Na1/2Bi1/2TiO3 (NBT) was studied by time-domain THz and microwave spectroscopy, using also previously published data and their new overall fits. Above the dielectric maximum temperature Tm ~ 600 K, the response consists of coupled sub-THz oscillator and a relaxation mode, assigned to strongly anharmonic Bi-ion vibrations and hopping, whose slowing down explains the paraelectric-like permittivity increase to Tm. Below Tm, the main relaxation continues slowing down and additional relaxation, assigned to quasi-Debye losses, appears in the 10^11 Hz range.…
Structural properties, impedance, dielectric and electric modulus spectra have been used to investigate the sintering temperature (Ts) effect on the single phase cubic spinel Ni0.6Zn0.4Fe2O4 (NZFO) ceramics synthesized by standard ceramic technique. Enhancement of dielectric constants is observed with increasing Ts. The collective contribution of n-type and p-type carriers yields a clear peak in notable unusual dielectric behavior is successfully explained by the Rezlescu model. The non-Debye type long range dielectric relaxation phenomena is explained by electric modulus formalism. Fast respo…
Using density-functional theory with ultrasoft pseudopotentials, we previously investigated the structural and electronic properties of the low-pressure (cubic, tetragonal, and monoclinic) phases of ZrO2 and HfO2, in order to elucidate phonon modes, Born effective charge tensors, and especially the lattice dielectric response in these phases. We now extend this previous work by carrying out similar calculations on the two high-pressure orthorhombic phases, and by providing density-of-states and band-gap information on all polymorphs. Our results show that the electronic structures and dielectr…
Realistic models of amorphous ZrO2 are generated in a ``melt-and-quench'' fashion using ab-initio molecular dynamics in a plane-wave pseudopotential formulation of density-functional theory. The structural properties of the resulting amorphous models are analyzed, with special attention to coordination statistics. The vibrational and dielectric properties of one of these models are then investigated from first principles using linear-response methods. The electronic dielectric constant and Born effective charges are found to be very similar to those of the crystalline phases. Encouragingly, th…
We present dielectric measurements of the colossal dielectric constant material CaCu3Ti4O12 extending up to 1.3 GHz also covering so far only rarely investigated single crystalline samples. Special emphasis is put on the second relaxation reported in several works on polycrystals, which we detect also in single crystals. For polycrystalline samples we provide a recipe to achieve values of the dielectric constant as high as in single crystals.
We investigate band gaps, equilibrium structures, and phase stabilities of several bulk polymorphs of wide-gap oxide semiconductors ZnO, TiO2,ZrO2, and WO3. We are particularly concerned with assessing the performance of hybrid functionals built with the fraction of Hartree-Fock exact exchange obtained from the computed electronic dielectric constant of the material. We provide comparison with more standard density-functional theory and GW methods. We finally analyze the chemical reduction of TiO2 into Ti2O3, involving a change in oxide stoichiometry. We show that the dielectric-dependent hybr…
We report far-infrared dielectric properties of powder form ferroelectric SrTiO3. Terahertz time-domain spectroscopy (THz-TDS) measurement reveals that the low-frequency dielectric response of SrTiO3 is a consequence of the lowest transverse optical (TO) soft mode TO1 at 2.70 THz (90.0 1/cm), which is directly verified by Raman spectroscopy. This result provides a better understanding of the relation of low-frequency dielectric function with the optical phonon soft mode for ferroelectric materials. Combining THz-TDS with Raman spectra, the overall low-frequency optical phonon response of SrTiO…
The authors of paper commented claim that trimethylammonium tetrachlorozincate crystal shows at 282 K the ferroelectric-paraelectric phase transition. But no ferroelectric hysteresis loop was observed below this temperature. Moreover, in the low-temperature phase the ferroelectric domain walls should exist giving dielectric relaxation in a low frequency electric field. The authors conclude that the phase transition is of the second order. This conclusion is contrary to the DSC data where the phase transition has a strong first order character. In the whole measured temperature range the dielec…
In this paper we demonstrate a quantitative way to measure the membrane potential of live cells by dielectric spectroscopy. We also show that the values of the membrane potential obtained using our technique are in good agreement with those obtained using traditional methods-voltage sensitive dyes. The membrane potential is determined by fitting the experimental dielectric dispersion curves with the dispersion curves obtain from a theoretical model. Variations in the membrane potential were induced by modifying the concentration of potassium chloride in the solution of the cell suspension in t…
The electronic structure and optical properties of metallic nanoshells are investigated using a jellium model and the Time Dependent Local Density Approximation (TDLDA). An efficient numerical implementation enables applications to nanoshells of realistic size with up to a million electrons. We demonstrate how a frequency dependent background polarizability of the jellium shell can be included in the TDLDA formalism. The energies of the plasmon resonances are calculated for nanoshells of different sizes and with different dielectric cores, dielectric embedding media, and dielectric shell backg…
We explore the frequency-dependent relative permittivity of Ruddlesden-Popper series Sr(n+1)Ti(n)O(3n+1) (n =1,2,3) thin films as a function of temperature and dc electric field. Interdigitated capacitors and coplanar waveguides were used to extract the frequency response from 500 Hz to 40 GHz. At room temperature, the in-plane relative permittivities obtained for Sr(n+1)Ti(n)O(3n+1) (n =1,2,3) were 42+/-3, 54+/-3, and 77+/-2, respectively, and were independent of frequency. At low temperatures, permittivity increases and electric field tunability develops in Sr(4)Ti(3)O(10).
We report first principles density functional calculations of the Born effective charges and electronic dielectric tensors for the relaxor PMN (PbMg1/3Nb2/3O3). Visualization of the Born charge tensors as charge ellipsoids have provided microscopic insights on the factors governing piezoelectric enhancements with polarization rotation. Several 15 and 30-atom ferroelectric and antiferroelectric supercells of PMN involving 1:2 and 1:1 chemical ordering have been studied. A cascading set of ferroelectric phonon instabilities lead to several low symmetry monoclinic structures. We find a ground sta…
For the first time, the dielectric response of a BaTiO3 thin film under an AC electric field is investigated using time-resolved X-ray absorption spectroscopy at the Ti K-edge to clarify correlated contributions of each constituent atom on the electronic states. Intensities of the pre-edge eg peak and shoulder structure just below the main edge increase with an increase in the amplitude of the applied electric field, whereas that of the main peak decreases in an opposite manner. Based on the multiple scattering theory, the increase and decrease of the eg and main peaks are simulated for differ…
We propose to measure the surface charge accumulating at the interface between a plasma and a dielectric by infrared spectroscopy using the dielectric as a multi-internal reflection element. The surplus charge leads to an attenuation of the transmitted signal from which the magnitude of the charge can be inferred. Calculating the optical response perturbatively in first order from the Boltzmann equation for the electron-hole plasma inside the solid, we can show that in the parameter range of interest a classical Drude term results. Only the integrated surface charge enters, opening up thereby …
Raman intensity of Rhodamine B (RhB) is enhanced by inserting a thin high \k{appa} dielectric layer which reduces the surface plasmon damping at the gold-graphene interface. The results indicate that the Raman intensity increases sharply by plasmonic resonance enhancement while maintaining efficient fluorescence quenching with optimized dielectric layer thickness.
The dielectric constant, which defines the polarization of the media, is a key quantity in condensed matter. It determines several electronic and optoelectronic properties important for a plethora of modern technologies from computer memory to field effect transistors and communication circuits. Moreover, the importance of the dielectric constant in describing electromagnetic interactions through screening plays a critical role in understanding fundamental molecular interactions. Here we show that despite its fundamental transcendence, the dielectric constant does not define unequivocally the …
Broadband dielectric spectroscopy from Hz up to the infrared (IR) range and temperature interval 10-300 K was carried out for xBaZrO3-(1-x)BaTiO3 (BZT-x, x = 0.6, 0.7, 0.8) solid solution ceramics and compared with similar studies for x = 0, 0.2, 0.4, 1 ceramics published recently (Phys. Rev. B 86, 014106 (2012)). Rather complex IR spectra without appreciable mode softening are ascribed to Last-Slater transverse optic (TO) phonon eigenvector mixing and possible two-mode mixed crystal behavior. Fitting of the complete spectral range requires a relaxation in the 100 GHz range for all the samples…
An impedance spectroscopy (IS) is a versatile tool to study the effect of grains (bulk), grain boundaries and electrode-electrolyte interface on dielectric and electrical properties of electro-ceramics. This study only focuses the high frequency (1 kHz to 10 MHz) probe of bulk ferroelectric capacitance near ferroelectric phase transition temperature (FPTT). The PZTFW single phase and PZTFW-CFO composites, respectively, have been investigated to understand the microstructure-property relation. Keeping in mind the complex microstructure of both systems, low frequency ( less than 1 kHZ ) impedanc…
We report calculations of the effective electronic response of aligned multishell carbon nanotubes. A local graphite-like dielectric tensor is assigned to every point of the multishell tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations. Calculations of both real and imaginary parts of the effective dielectric function are presented, for various values of the filling fraction and the ratio of the internal and external radii of hollow tubules. Our full calculations indicate that the experimentally measured macroscopic dielectric …
In this paper the synthesis and study of the structural, morphological, electrical, magnetic and electronic properties of the LaBiFe2O6 novel material are reported. The material was produced using the standard ceramic method. The Rietveld analysis of experimental data of x-ray diffraction showed that it synthesizes in an orthorhombic perovskite structure (Pnma, #62 space group). Two types of grain, micro and submicrometric, with the LaBiFe2O6 stoichiometry were identified by scanning electron microscopy and X-ray dispersive spectroscopy. Results of electrical polarization and dielectric consta…
In the present work the authors report results of broadband dielectric spectroscopy on various samples of CaCu3Ti4O12, including so far only rarely investigated single crystalline material. The measurements extend up to 1.3 GHz, covering more than nine frequency decades. We address the question of the origin of the colossal dielectric constants and of the relaxational behavior in this material, including the second relaxation reported in several recent works. For this purpose, the dependence of the temperature- and frequency-dependent dielectric properties on different tempering and surface tr…
Based on first-principles calculations, we systematically study the electronic, dielectric, and plasmonic properties of two-dimensional (2D) electride materials X$_2$N (X=Ca, Sr). We show that both Ca$_2$N and Sr$_2$N are stable down to monolayer thickness. For thicknesses larger than 1-monolayer (1-ML), there are 2D anionic electron layers confined in the regions between the [X$_2$N]$^+$ layers. These electron layers are strongly trapped and have weak coupling between each other. As a result, for the thickness dependence of many properties such as the surface energy, work function, and dielec…
We demonstrate a simple and robust methodology for measuring and analyzing the polarization impedance appearing at interface between electrodes and ionic solutions, in the frequency range from 1 to $10^6$ Hz. The method assumes no particular behavior of the electrode polarization impedance and it only makes use of the fact that the polarization effect dies out with frequency. The method allows a direct and un-biased measurement of the polarization impedance, whose behavior with the applied voltages and ionic concentration is methodically investigated. Furthermore, based on the previous finding…
We formulate a general theory of the dielectric response of a lattice with a structural transition and a polarization instability due to a soft-optic mode coupled to low energy electronic excitations by the electromagnetic fields. the electronic excitations considered are in two-limits; those of a low density of free-electrons or those of a low density of strongly localized electrons in the Coulomb-glass phase. The ferroelectric transition in the absence of the electronic-excitations and the low energy dielectric properties are shown to be strongly modified.
Hexagonal boron nitride (h-BN) is a critical material for 2D electronic devices for graphene and has attracted a considerable amount of attention owing to its structural similarity and semiconducting property. However, modifying its wide-band gap is a challenge. Hydrogenation is a potential method of altering the electrical properties, although is seldom experimentally measured. Here, the complex permittivity of h-BN after various hydrogen treatments have been investigated. For untreated h-BN, a frequency independent dielectric constant was measured ($\sim4.2 \pm0.2$) and an immeasurably low d…
We present a first-principles calculation of the electronic properties of crystalline silicon and gallium arsenide in a uniform electric field. Polarized Wannier-like functions which are confined in a finite region are obtained by minimizing a total-energy functional which depends explicitly on the macroscopic polarization of the solid. The polarization charge density and the electronic dielectric constant are computed via finite differences. The results coincide with those of the linear response approach in the limit of vanishing electric field and infinite localization region.
Dielectrics are insulating materials used in many different electronic devices and play an important role in all of them. Current advanced electronic devices use dielectric materials with a high dielectric constant and avoid high leakage currents. However, these materials show several intrinsic problems, and also a bad interaction with adjacent materials. Therefore, the race for finding a suitable dielectric material for current and future electronic devices is still open. In this context two dimensional [2D] materials have become a serious option, not only thanks to their advanced properties,…
Polymer-based nanocomposite dielectrics are expected to become essential in future generations of high voltage electrical insulation. However, the physics behind their performance is not yet understood. Here we investigate electronic properties of the interfacial area in magnesium oxide-polyethylene nanocomposite. We use density functional theory to calculate densities of states for MgO (100) and hydroxylated MgO (111) interfaces with polyethylene. We evaluate the role of silicon-based nanoparticle surface modification at the electronic level and propose a new theory for charge trapping in nan…
Heterostructures of van der Waals bonded layered materials offer unique means to tailor dielectric screening with atomic-layer precision, opening a fertile field of fundamental research. The optical analyses used so far have relied on interband spectroscopy. Here we demonstrate how a capping layer of hexagonal boron nitride (hBN) renormalizes the internal structure of excitons in a WSe$_2$ monolayer using intraband transitions. Ultrabroadband terahertz probes sensitively map out the full complex-valued mid-infrared conductivity of the heterostructure after optical injection of $1s$ A excitons.…
We report on phonon properties and electronic transitions in CaCu3Ti4O12, a material which reveals a colossal dielectric constant at room temperature without any ferroelectric transition. The results of far- and mid-infrared measurements are compared to those obtained by broadband dielectric and millimeter-wave spectroscopy on the same single crystal. The unusual temperature dependence of phonon eigenfrequencies, dampings and ionic plasma frequencies of low lying phonon modes are analyzed and discussed in detail. Electronic excitations below 4 eV are identified as transitions between full and …
In this article mixed CuInP$_2$(S$_x$Se$_{1-x}$)$_6$ crystals were investigated by broadband dielectric spectroscopy (20 Hz - 3 GHz). The complete phase diagram has been obtained from these results. The phase diagram of investigated crystals is strongly asymmetric - the decreasing of ferroelectric phase transition temperatures in CuInP$_2$(S$_x$Se$_{1-x}$)$_6$ is much more flat with small admixture of sulphur then with small admixture of selenium. In the middle part of the phase diagram (x=0.4-0.9) the dipolar glass phase has been observed. In boundary region between ferroelectric order and di…
We propose a fully ab initio theory to compute the electron density response under the perturbation in the local field. This method is based on our recently developed local dielectric response theory [Phys. Rev. B 92, 241107(R), 2015], which provides a rigorous theoretical framework to treat local electronic excitations in extended systems beyond the commonly employed dipole approximation. We have applied this method to study the electronic part of the molecular polarizability of water in ice Ih and liquid water. Our results reveal that the crystal field of the hydrogen-bond network has strong…
The electronic structure of two-dimensional (2D) materials are inherently prone to environmental perturbations, which may pose significant challenges to their applications in electronic or optoelectronic devices. A 2D material couples with its environment through two mechanisms: local chemical coupling and nonlocal dielectric screening effects. The local chemical coupling is often difficult to predict or control experimentally. Nonlocal dielectric screening, on the other hand, can be tuned by choosing the substrates or layer thickness in a controllable manner. Therefore, a compelling 2D electr…
We report the high temperature dielectric and {\it ac} impedance spectroscopy investigation of Nb substituted LaCo$_{0.7}$Nb$_{0.3}$O$_3$ polycrystalline sample. The maximum dielectric constant value was observed $\approx$1400 at around 400~K where the peak value shows a decreasing trend at higher temperatures and frequency. Similar variation was reflected in the dielectric loss (tan$δ$) behavior with temperature, which shows the thermal activation of the charge carriers in the material. The analysis of high temperature impedance spectroscopy data shows the grain and grain boundary contributio…
Dielectric screening plays an important role in reducing the strength of carrier scattering and trapping by point defects for many semiconductors such as the halide perovskite solar materials. However, it was rarely considered as a screen to find new electronic semiconductors. We performed a material search study using the dielectric properties as a screen to identify potential electronic materials in the class of metal-pnictide ternary sulfosalts, containing Bi or Sb. These salts are basically ionic due to the electronegativity difference between the S and both the metal and pnictogen element…
We present a novel method for the calculation of the static and electronic dielectric tensor of polar insulating crystals based on concepts from the modern theory of dielectric polarization. As an application, we present the first ab initio calculation of the dielectric constants in the wurtzite III-V nitrides AlN, GaN, and InN.
Optical pump-probe spectroscopy is a powerful tool for the study of non-equilibrium electronic dynamics and finds wide applications across a range of fields, from physics and chemistry to material science and biology. However, a shortcoming of conventional pump-probe spectroscopy is that photoinduced changes in transmission, reflection and scattering can simultaneously contribute to the measured differential spectra, leading to ambiguities in assigning the origin of spectral signatures and ruling out quantitative interpretation of the spectra. Ideally, these methods would measure the underlyin…
F+ center, an electron trapped at oxygen vacancy (VO), was investigated in the oxygen deficient Y3Al5O12 (YAG) crystals by EPR. The measurements were performed at temperatures 5-450 K and frequencies 9.4-350 GHz with using both the continue wave and pulse EPR technique. The pulse electron-nuclear double resonance was applied to resolve the hyperfine interaction of the trapped electron with surrounding nuclei. The measurements show that at low temperatures, T < 50 K, EPR spectrum of the F+ center is anisotropic with g factors in the range 1.999-1.988 and originates from three magnetically inequ…
