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The broad peak of the non-linear AC susceptibility around the spin-glass temperature (T_g) of amorphous Fe₉₃Zr₇ suggests that the paramagnetic to spin-glass transition at T_g is determined by the superparamagnetic behaviour of magnetic clusters.

We have examined specimens of vitreous a-As₂Se₃ using transient photocurrent techniques. These techniques allowed us to probe the electronic states contained within the mobility gap of this material. Analysis of the unique transient photocurrent data reveals a structured density of states rather than a broad featureless distribution which is sometimes said to exist in this material.

Over the past two decades or so, the positron annihilation technique has successfully probed Fermi surface (FS) topologies in a variety of metals and alloy systems. However, in electronically complex systems, due to the relatively weak FS signals compared with those arising from annihilations from a large number of full bands, possible strong positron wave function comes into effect. Here, we introduce a new way of looking at the problem using maximum-entropy enhancement of the data. Test results from the simple FS picture of vanadium are presented.

Thin films have been prepared by electron beam evaporation of strontium titanate (SrTiO₃) on bare (111) p-type silicon substrate held at room temperature. The as deposited films were annealed at 700 degrees C in flowing oxygen to compensate for any loss of O from the sample. The as deposited and the annealed samples were analysed by Auger electron spectroscopy (AES). The AES analysis shows that there is no trace of Si present in the bulk of the film and the Si/film interface is fairly sharp. The results are discussed in the light of the usefulness of the e-beam deposition of SrTiO₃ for preparation of a buffer layer on an Si substrate for the deposition of high-T_c superconducting materials in thick- and thin-film form.

Spin-dependent electrical resistivity due to scattering by displaced interface atoms has been computed for a layered CuCo superlattice, using full-potential multiple-scattering theory with no free parameters. The magnetoresistance ratio Delta R/R( up arrow up arrow ) obtained for this scattering mechanism is 25.03. When interface resistivity, weighted by interpretation concentration c approximately=0.10, is combined with bulk resistivity, Delta R/R is in the expected experimental range for adjacent CuCoCu layers. This resistance mechanism produces spin-dependent steady-state chemical potentials, relevant to the bipolar spin switch.

We have utilized x-ray photoelectron and variable energy positron beam spectroscopies for depth profiling excess arsenic, arsenic precipitates, and vacancy-type defects in GaAs grown by molecular beam epitaxy at low temperatures (LT-GaAs). XPS results show about 1.3% excess arsenic in as-grown LT-GaAs and a non-uniform depth profile of arsenic concentration in annealed LT-GaAs. Doppler broadening of the positron-electron annihilation radiation (S parameter) reveals a non-uniform depth profile of defects in annealed LT-GaAs. We observe a clear correlation between the depth profile of the S parameter and As in annealed LT-GaAs.

There is increasing evidence that there exists a class of adsorbate-induced reconstructions of metal surfaces in which the outermost substrate layer (or layers) and the adsorbed species adopt an almost identical geometry on surfaces of several different orientations of the same substrate; on one orientation this involves little or no substrate distortion, but on the others, major reconstruction is required. There is also evidence that the adsorption structure on the unreconstructed orientation surface may have a particularly low surface free energy. This type of reconstruction therefore appears to offer an atomistic alternative to the more microscopic phenomenon of adsorbate-induced faceting. By reviewing the existing structural information concerning the adsorbate structures of S on Ni, Cu and Pt, C and N on Ni and Cu and O on Cu, the evidence for this idea, and for some complementary patterns of adsorbate-induced reconstruction, are discussed. These data on the long-range-ordered phases on the (100), (111) and (110) faces of these materials are compared with the limited data available on the influence of the adsorbates on the anisotropy of the surface free energy, or gamma -plot.

The Brillouin light scattering technique has been exploited in order to study the elastic properties of finite-stage a-Si:H/a-Si_1-xC_x:H semiconductor quasiperiodic Fibonacci multilayers, deposited by plasma enhanced chemical vapour deposition on crystalline silicon, fused quartz and corning glass substrates. Detection of the Rayleigh surface acoustic mode enabled us to study the evolution of the phase velocity of this mode as the number of Fibonacci stages is increased from eight to twelve and to evaluate the effective elastic constant c₄₄. The values obtained in these finite-stage Fibonacci structures are consistent with those calculated, by means of the effective modulus model, for an infinite quasiperiodic structure. In contrast to the anomalous elastic behaviour previously found in metallic superlattices, no elastic anomaly has been observed in the a-Si:H/a-Si_1-xC_x:H amorphous semiconductor multilayers, in agreement with recent theoretical models, which predict the presence of elastic anomalies in cases of symmetry difference and lattice mismatch between adjacent crystalline layers. Moreover, a slight decrease of the Rayleigh mode velocity has been observed on changing the substrate from c-Si to corning glass or fused quartz.

The adsorption structures and dissociation properties of PH₃ on Si(100)2*1 and Si(111)7*7 have been studied by the ASED MO method. Our calculation results show that, on the Si(100)2*1 surface, PH₃ is adsorbed undissociatively on the dangling bond, with a binding energy of 2.25 eV, Si-P bond length of 2.23 AA, an angle from the surface normal of 22 degrees , a P-H bond length of 1.52 AA and an angle of the PH₃ axis to the surface normal of 21 degrees . The dissociation energy barrier of the first H atom for PH₃ is about 1.61 eV, in agreement with the experimental results of molecular adsorption of PH₃ on Si(100) at room temperature. On S(111)7*7, the most stable site for PH₃ adsorption of S₂DB and then the S₁DB site; the binding energies are 2.11 eV and 1.00 eV, respectively. Using the DAS model in our calculation, our results show, that the energy barrier for PH₃ dissociation on S₁DB and S₂DB are 1.02 eV and 2.05 eV, respectively. If we replace the Si adatom in the DAS model by a Si₄ small cluster, the binding energies of PH₃ on S₂DB and S₁DB are 1.64 eV and negative, respectively. The dissociation energy barrier on S₂DB will reduce to 0.48 eV. It seems that the dissociation of PH₃ on Si(111)7*7 is caused by some kind of defect on this surface.

We study the growth of the c(2*2) structure of Pb on Ni(001) with high-resolution x-ray diffraction. By monitoring the adsorbate-substrate and the adsorbate-adsorbate interference diffraction peaks, we are able to determine the registry and growth process of the first overlayer. Pb atoms change from hollow site to non-hollow site growth as coverage increases. Results at higher substrate temperatures indicate a different growth process at low coverage. We propose a model of adsorbate aggregation at sites in line with Ni atoms around pinning centres to account for the observed results.

Carbon nitride thin films have been prepared by NH₃-ion-beam-assisted deposition with bombardment energies of 200-800 eV at room temperature. These films have been characterized by transmission electron microscopy, Auger electron spectroscopy and x-ray photoelectron spectroscopy for chemical analysis. It was found that the structure of the films varied with the bombardment energy. In the case of 400 eV bombardment, the tiny crystallites immersed on an amorphous matrix were identified to be beta -C₃N₄. X-ray photoelectron spectroscopy indicated that some carbon atoms and nitrogen atoms form unpolarized covalent bonds in these films.

Interest in electron transport on high-index GaAs surfaces is increasing, especially since the advent of patterned substrate regrowth, in which high index surfaces are revealed on (001) GaAs after etching. In this paper we observe anisotropic mobility in orthogonal directions in two-dimensional electron gases grown on (311)B GaAs substrates. The mobility in the (233) direction is found to be up to 50 in the (011) direction. The lower mobility is accompanied by a large anomalous negative magnetoresistance. These effects are studied as a function of temperature and carrier density. It is suggested that interface roughness scattering could be a cause for the large anisotropies in mobility and a simple calculation is performed to demonstrate this hypothesis.

We have developed a theory of the quantum acoustomagnetoelectric effect due to Rayleigh sound waves in the presence of a quantizing magnetic field normal to the crystal-vacuum interface. Electrons are assumed to be specularly reflected at the sample surface. For this case we predict the appearance of an acoustoelectric current along the 'Hall' direction orthogonal both to the magnetic field and to the wavevector of the Rayleigh sound. We also predict quantum oscillations of this current analogous to the de Haas-van Alphen and Shubnikov-de Haas oscillations. We show that in the quantum strong-field limit the current oscillations cease to be a small correction to the monotonic part of the current and can have a large amplitude.

The electrical resistivity, Hall effect and magnetoresistance of Cu/Ni sputtered multilayer films were measured between 1.6 and 300 K for a series of different layer periodicities Lambda . For small Lambda we observed anomalies in the resistivity versus T curves which we interpret as reflecting a reduction in the Curie temperature of these samples. The magnetoresistance at 4.2 K increases with decreasing Lambda to about 9.3% for Lambda of 2.7 nm compared with 0.3% for a pure Ni film of 500 nm thickness. The anomalous part of the Hall resistivity also increases with decreasing Lambda , which suggests that the magnetic interface scattering might enhance the side-jump scattering.

Raman spectroscopy has been employed to investigate the microstructural features of strained Si-Ge layers deposited by the rapid-thermal-process very-low-pressure chemical vapour deposition method. Auger electron spectroscopy was used to determine the Ge concentrations in the Si-Ge layers. The Ge atoms in the high-Ge-concentration Si-Ge alloy are distributed more homogeneously and randomly than in the low-Ge-concentration alloy. The substrate temperature has a great influence on the microstructure of the strained Si-Ge alloy. A high Ge content needs a relatively low substrate temperature to deposit high-quality Si-Ge alloy, but a low Ge content requires a higher growth temperature during the deposition of the Si-Ge alloy.

The characterization and interaction between Cl atoms on the Si(100)2*1 surface have been studied by the atom superposition and electron delocalization molecular orbital theory, using 2*1 symmetric- and buckled-dimer models for this surface. Two stable adsorption sites for Cl bonding have been found in the symmetric-dimer model. One is along the surface dangling bond, with a Cl-Si bond length of 1.97 AA and a bond angle of 21 degrees to the surface normal; the other is the bridge site with a Cl-Si bond length of 1.99 AA. The adsorbed Cl atom on the bridge site will block further adsorption on the dangling-bond site in the same Si dimer. A reasonable explanation for slowing chlorine adsorption kinetics at a coverage of about 0.7 Cl/Si is given. In the buckled-dimer model, Cl is predicted to adsorb onto the dimer up-atom site, with a Cl-Si bond length of 1.92 AA and a bond angle of 19 degrees . We guess that the buckled dimer on the Si(100)2*1 surface will be converted into a symmetric dimer after Cl adsorption.

High-resolution x-ray scattering was performed on a decaprismatic sample of the nominal composition Al₇₀Co₁₅Ni₁₅. The overall diffraction pattern has tenfold symmetry within experimental resolution. But many low-indexed reflections reveal a splitting, which is evidence for twinned high-order periodic approximants of the decagonal phase, rather than for a truly decagonal quasicrystal. To our knowledge. We report the clearest separation of this kind of splitting to date. For the orthorhombic approximant, the space group Ccmm with lattice parameters a=61.024(5) AA, b=83.99(1) AA and c=4.0799(5) AA was derived. Deviations from the diffraction pattern predicted by the twinning model were observed. We point out the close similarity between the x-ray diffraction of the real decagonal quasicrystal and that of our twinned sample.

Various comparative experiments on xPbCl₂-(100-x)B₂O₃(20<or=*<or=45 mol%) glasses reveal that the PbCl₂ does not enter the B-O network, but is inserted into interstices or voids in the glassy matrix. However, the network becomes systematically weakened and expanded with increasing PbCl₂ concentration; this is observed as a decrease in T_g, and an increase of both the molar volume and thermal expansion coefficient. The electrical conductivity measurements of these glasses demonstrated a marked enhancement in the ionic conductivity ( sigma ). The maximum enhancement in sigma is by eight orders of magnitude as PbCl₂ replaces B₂O₃(45 mol%). The drastic increase in sigma leads us to suggest that the Cl^- ions form additional migration pathways for Pb²⁺ ions, which are important for the conduction mechanisms. In addition, the activation energy associated with jumping Pb²⁺ ions decreases with increasing PbCl₂ content; this indicates that jumps of the Pb²⁺ ions in the vicinity of the Cl^- ions are relatively easy.

We examine the free electron model for some rational approximants of 2D quasicrystals and quasi-lattices that exhibit quasiperiodicity in (x, y) planes and periodicity along the z-direction. Our study is based on a scattering potential with ten symmetrically oriented plane-wave components in the (k_x, k_y) plane for the 2D case, and two additional plane-wave components in directions perpendicular to the plane for the 3D case. We calculate the band structure and the density of states for the rational approximants and examine the formation of a gap or a pseudogap in such systems. The relevance of this study to the stability and electrical conduction property of decagonal quasicrystals is discussed.

The temperature dependence of the phonon dispersion of Nb from room temperature up to 2223 K has been measured by means of inelastic neutron scattering. Over a temperature range of nearly 2000 K the dispersion changes only moderately. Effects due to electron-phonon interaction almost vanish at the highest temperature. Parameterizing the dispersion curves by Born-von Karman force constants, the phonon density of states g( omega ) at different temperatures was computed. Employing the model of phonon controlled diffusion in BCC metals, the migration barrier H^m and the formation entropy S^f have been calculated. The results agree with those of quenching and electron irradiation experiments.

Bismuth tetratitanate, Bi₂Ti₄O₁₁, undergoes a paraelectric-to-antiferroelectric phase transition at about 233 degrees C. The integrated intensities of selected x-ray reflections and the linear optical excess birefringence have been measured as a function of temperature for Bi₂Ti₄O₁₁ to characterize the transformation. Both methods indicate a continuous transition with a critical exponent of 1/4 . From the change of the lattice constants with temperature the scalar spontaneous strain, epsilon _s, can be calculated. In the present case of a zone boundary transformation, epsilon _s² couples quadratically with the primary order parameter. The observed linear dependence of epsilon _s² on the temperature T points once again to the tricritical nature of the transition. Despite the mean field behaviour of the transition inferred from these results, diffuse intensities at the positions of superlattice reflections just above T_c may be attributed to the existence of non-classical order parameter fluctuations. Taking this observation into account the transformation can be designated as almost tricritical.

The soliton scattering by one single and two point impurities in a finite domain of an infinite phi ⁴ chain is analytically discussed. It is shown. For the single-point-impurity configuration, that the impurity causes the soliton to oscillate about the host site, whereas for the two-point-impurities configuration the soliton oscillates from one impurity wall to the other of the finite domain delimited by the two host sites. The oscillation frequency in each configuration has been estimated. We have also shown that in the second configuration the soliton falls into the finite domain with an exponentially increasing velocity and escapes at the transmitting wall with a velocity that decreases exponentially as the domain thickness increases.

The growth of thin Ag₂S films on silver layers from diluted H₂S gas has been studied by means of in situ ellipsometric and DC conductivity measurements. The experimental data from the ellipsometric studies were explained by means of a model consisting of silver and Ag₂S films and a thin layer of H₂O of variable thickness on top of them. The variation in the conductivity of the silver layer could be explained on the basis of the decreasing thickness of the silver layer when a thin Ag₂S film grew on it, together with the increasing reflection of the current carriers from the grain boundaries.

The density of states (DOS) of the Bloch electron on a two-dimensional (2D) lattice in an external perpendicular magnetic field is exactly calculated in the case of a rational flux through an elementary cell in the model with exponentially decreasing, as a function of inter-site spacing, overlap integrals. A generalization of this model to the case of an array of parallel chains with tight-binding correlations between them is considered, and the appropriate DOS is calculated. A quasiclassical quantization rule is obtained for arbitrary electron dispersion along the chains in the low-flux limit, which yields, for energies near the band bottom, Landau levels that broaden into bands of width proportional to a magnetic breakdown-like probability factor. The analogy between the Wannier-Stark ladder and the Landau spectrum for a Bloch electron on a 2D lattice is considered. Possible applications to organic conductors and superconducting superlattices are discussed.

We establish the existence of an absolute frequency gap of the electromagnetic field in photonic crystals with tetragonal symmetry, and examine the dependence of the gap on the geometry of the structure. We calculate the transmittance through a slab of finite thickness of the material, and show that planar defects in the slab produce interface states of the electromagnetic field, at frequencies within the photonic gap, manifested by sharp resonances in the transmittance of these systems.

A detailed theoretical study of the emission rate of the acoustic (AC) phonons is presented for AlGaAs-GaAs-AlGaAs single quantum wells (SQWs). The electron interacting with AC phonons via the deformation potential and piezoelectric coupling is taken into account, We consider the situations where one and two electronic subbands are occupied by electrons, using the results obtained from our self-consistent calculations on the electronic structure. The angle and energy dependences of the AC phonons generated in a GaAs-based two-dimensional electron gas (2DEG) are determined entirely by momentum and energy conservation during the electron-phonon scattering event, in contrast with the process of phonon generation in Si-based structures. Our results show that, in the phonon frequency range omega _Q approximately 10¹² Hz, the phonons with higher frequency can be detected at smaller emission angles. The phonons generated through the intersubband scattering processes have a more marked angle dependence and larger emission rate than those generated by intrasubband scattering processes.

This paper presents a two-SO-coupling-parameter model, in which not only the contribution due to the SO coupling of the central TM ions but also that of the ligand ions are included, for the calculation of the g-factors and the anisotropy Delta g(=g_z-g_x) of the trigonal d³ cluster. The calculated results for VCl₂ and VBr₂ show that the contribution to both g and Delta g due to the SO coupling of the ligand ions is small in VCl₂ but is sufficiently important in VBr₂, about 85% for g and 40% for Delta g. It suggests that in the calculation of g and Delta g the two-SO-coupling-parameter model should be preferred in the case of heavy-element ligand ions such as Br^- ions.

Linear and non-linear transport properties of carriers in non-parabolic Kane bands are investigated using the two extended balance equations introduced by Magnus, Sala and De Meyer (MSD) (1990) and by Lei (1992,1994). Formally, the MSD equations describe the motion of a single particle with fixed charge and fixed mass, while the Lei equations describe the motion of a single particle having fixed charge but variable effective mass. In the parabolic limit these two sets of equations are identical and reduce to the original Lei-Ting balance equations. In the non-parabolic case, although the linear resistivities predicted by the Lei and MSD equations are nearly the same for weakly to medially non-parabolic systems, non-linear drift-velocity-field behaviour obtained from these two sets of equations shows marked differences for medial and strong non-parabolicity. The reasons for these differences are discussed.

Non-linear propagation of ultra-short lateral circularly polarized strain pulses in a paramagnetic crystal of cubic symmetry localized in an external magnetic field at super-low temperature has been studied. The direction of the magnetic field is parallel to the direction of pulse propagation and the fourth-order symmetry axis. Under certain physical conditions pulse propagation is described by the 'derivative non-linear Schrodinger equation', which belongs to the equations integrated by the inverted scattering transform method. The phenomenon of full reflection of acoustic pulses on the paramagnetic crystal surface is predicted. The possibility of continuous parametric increase of frequency of a high-power acoustic signal during its passage through the paramagnetic crystal has been shown. This frequency increase can be controlled through changes in the power of the incoming signal. In this direction in principle one can obtain 10-fold frequency increase of an initial pulse. As an example the crystal MgO with impurities of paramagnetic ions Co²⁺ is considered.

The thermal conductivities of YBa₂(Cu_1-xFe_x)₃O_{7- delta} +y% CuO ceramics for 0<x<0.03 and 0<y<5 have been measured. The thermal conductivities of all samples exhibit a minimum in the vicinity of the critical temperature T_c and a maximum near T_c/2. These results are interpreted with the help of an electronic model, i.e. supposing that the main contribution to the thermal conductivity below T_c is due to electron scattering in the CuO₂ planes. Within a simple two-fluid model derived from kinetic theory, taking into account the temperature dependence of the electronic relaxation time and the normal charge carrier concentration, we obtain theoretical curves which reproduce the experimental results quite well. We also take into account the porosity of the samples (in term of an intergrain contribution) to derive the electronic thermal conductivity. The parameter values of the model and the observed minimum are explained in terms of physical properties. In particular, the contribution of superconductivity fluctuations to the thermal conductivity is shown to be negligible with respect to other mechanisms.

Calculations of the phase transition temperature and the critical concentration of electric dipoles which induce in the host crystal lattice the phase transition with the appearance of long-range order are carried out. These calculations are made by considering the additional static random electric fields owing to defects of other types: elastic dipoles and point electric charges. The distribution function of the joint action of the aforementioned random fields is also calculated. It is shown that the presence of the defects of other types inhibits phase transition so that, for the occurrence of long-range order, in this case larger concentrations of electric dipoles are necessary. The theoretical results obtained are found to be important for a description of the experimental situation in K_1-xLi_xTaO₃, PbMg₁3/Nb₂3/O₃ and other disordered ferroelectrics.

High-resolution (0.05 cm^-1) FTIR spectroscopy in the temperature range 9-320 K has been used to monitor the narrow line absorption spectra, induced by the stretching modes of OH and OD impurities in as-grown and in-deuterated samples of BSO, BGO, mixed (1-x)BSO.xBGO, and BTO sillenite single crystals (i.e. Bi₁₂MeO₂₀ with Me=Si, Ge and Ti). The model of the anharmonic oscillator in the Morse potential was applied to interpret the observed spectra and the anharmonicity parameter x_e determined. For the line peaking at 3442.84 cm^-1 in BSO both the fundamental and the first overtone transitions were detected: in this way the complete set of the Morse parameters could be determined. A model for the OH centre is proposed on the basis of the dependence of the line position against lattice constant in all the systems examined. The phonon coupling of the stretching modes observed was studied by analysing the detailed temperature dependence of the line position and width. In the framework of weak coupling theory the frequencies of coupled phonons were determined and found to be in agreement with those obtained by reflectance, Raman scattering measurements and theoretical calculations.

The 2.7 eV photoluminescence emission ('gamma' band) has been studied in neutron-irradiated high-purity synthetic silica, both under UV and VUV (vacuum ultraviolet) excitation. Some aspects of the 5 eV excitation band, which is already known to exist, have been studied in great detail, while an excitation band centred at about 7.7 eV has been analysed for the first time. The intensity of the gamma emission for 5 eV excitation changes as a function of temperature in a completely different way to that for 7.7 eV excitation. In the latter case the emission intensity is constant up to about 300 K; a non-radiative decay predominates at higher temperatures. For excitation at 5 eV, the 'anomalous' increase of the emission that is already known to occur is observed as the temperature rises up to 500 K. We have developed a phenomenological model relating to the electronic levels of the luminescence centre that fits the experimental data well.

Precise photoluminescence measurements have been carried out on RbCdF₃:Mn²⁺ in the 9-300 K range to explore the structural phase transition of the host lattice at T_c=124 K using the first (M₁) and second (M₂) moments of the emission band together with the lifetime tau as probes. Aside from showing a sensitivity of M₂(T) and tau (T) to the phase transition, the present data reveal that the curve M₁(T) experiences a small but observable change of slope in the vicinity of T_c. It is demonstrated that this jump, Delta _t( delta M₁/ delta T)_P=0.22 cm^-1 K^-1, is mainly associated with the increase experienced by the local thermal expansion coefficient below T_c. The importance of both the implicit and explicit contributions to M₁(T) is analysed throughout this work. Neither the luminescence nor the excitation spectrum shows any evidence of tetragonal distortion in the MnF₆^4- complex. This fact is explained through the R_ax-R_eq=0 2 pm value (where R_ax and R_eq are the axial and equatorial Mn²⁺-F^- distances) at 30 K, and the coupling coefficient V_E=66 cm^-1 pm^-1 with the E_g Jahn-Teller mode of MnF₆^4-. Finally, we have found that this crystal exhibits photochemical reactions under UV light irradiation, leading to the formation of centres that transfer easily to Mn²⁺ ions. These centres give rise to an intense absorption band at 310 nm, analogously to those previously formed under x-irradiation.

Hydrogen diffusivities D in C14-ZrCr₂H_0.4 and C15-ZrCr₂H_x (0.2<or=*<or=0.5) have been measured by means of pulsed-field-gradient nuclear magnetic resonance over the temperature range 130-430 K. In all the samples studied the temperature dependence of D follows an Arrhenius law above 200 K but shows marked deviations from Arrhenius behaviour below about 180 K. This suggests that different diffusion mechanisms dominate at high and low temperatures. The jump length of H atoms estimated by comparing D(T) and the proton spin-lattice relaxation rates appears to be greater than the closest distance between tetrahedral (Zr₂Cr₂) sites occupied by hydrogen in these compounds. A diffusion model that considers jumps between next-nearest-neighbour (Zr₂Cr₂) sites via metastable (ZrCr₃) sites is discussed.

The bound magnetic polaron (BMP) in a cubic Fe-based diluted magnetic semiconductor is considered. It is shown that the energy spectrum of the BMP is identical to that of the three-dimensional harmonic oscillator with a spin-orbital coupling. The polaron effect manifests itself in the existence of a splitting in the energies of the excited states of the polaron. It is shown also that the g-factor of the BMP is smaller than the g-factor of a free electron calculated in the molecular-field approximation.