Resonant inelastic scattering in dilute magnetic semiconductors by soft X-ray fluorescence spectroscopy

1-x Mn_xS (where 0.05<x<1) were measured as the energy of the exciting radiation was tuned across the S and Mn-L_2,3 absorption edges of these compounds. Strong resonance peaks in Mn-L emission spectra and the systematic appearance of new spectral features in S-L emission spectra were observed. Partial substitution of Zn by a magnetic Mn ion results in strong hybridization of the Mn 3d orbitals with the sp band of the host semiconductor. A detailed study of resonant inelastic scattering in the vicinity of the S and Mn-L_2,3 absorption edges of these DMS is presented. Received: 6 March 1997     

Crystal field spectroscopy by inelastic neutron scattering

We present a review of inelastic neutron scattering results on very diluted rare earth (RE)-Laves phases. A systematic investigation to study crystal electric fields, experienced by single rare earth ions in a metallic environment, was done on (RE,R)Al₂, with RE=Pr, Nd, Tb, Dy, Ho, Er, Tm andR=Sc, Y, La. We show the influence of the 4f-ions on the crystal fields as well as the influence of the host lattices. The rare earth atoms in ScAl₂ have been studied for the first time and most of the other alloys, with LaAl₂ and YAl₂ as hosts, have been studied for the first time with magnetic atom concentrations below 1 at% and/or with good resolution for low energy excitations. Furthermore we studied the dynamics of 4f-moments, which are coupled to the conduction electrons by determining the coupling constants. We present a comprehensive set of crystal field parameters and coupling constants from these systematic studies and discuss them qualitatively within the available theoretical models. The influence of magnetic atom concentration on crystal field spectra will be shown in part II.     

Excitation of levels by inelastic neutron scattering

A scintillation spectrometer in ring geometry was used to study the gamma rays accompanying the inelastic scattering of fast neutrons on Na, Mg, Mn, Fe and I. The energies of the gamma rays were in most cases arranged into the cascade decay schemes of excited nuclei. Some of the transitions, which had not yet been described, were also found. These are the lines (2147±21) keV for Mg²⁵, (2135±22) keV, (2750±40) keV, (3040±50) keV and (3200±50) keV for Mn⁵⁵ and a series of other gamma rays emitted during the interaction of fast neutrons with I¹²⁷, which are given in the paper.

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-, Na, Mg, Mn, Fe I. - . , , . (2147±21) keV y Mg²⁵, (2135±22) keV, (2750±40) keV, (3040±50) keV (3200±50) keV y Mn⁵⁵ -, c I¹²⁷, .

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In conclusion the authors thank Z. Janout for contributing to the experimental work, J. Vrzal for the design of some of the apparatus, and F. trba, lecturer at the Faculty of Technical and Nuclear Physics, for help during the measurements. Thanks go to members of the accelerator laboratory staff of the Institute of Nuclear Research J. SchÄferling, J. Filípek and particularly J. Jirou, and to J. Zikmund from the same institute for valuable advice and help in the chemical problems connected with the measurements.     

Light scattering from magnons in ferromagnetic semiconductors

The effect of the electron-magnon interaction on the Raman scattering by magnons is discussed. It is shown that in addition to Loudon's spin-orbit coupling mechanism there is another, carrier-mediated, contribution to the Raman line. The frequency dependence of the resonant scattering is discussed and application to CdCr₂Se₄ is made.     

Heisenberg pentamer: insights into inelastic neutron scattering on magnetic clusters

Assuming Heisenberg interactions and the symmetric case of a spin S-S' pentamer, the energy eigenstates can be determined exactly. With the energies known, the inelastic neutron scattering intensities are then calculated for the special case of a 1-1/2 pentamer. Through an analysis of these results, two main insights are gained. (1) Because of symmetry constraints, not all ΔS(tot) = ±1 transitions are accessible by inelastic neutron scattering (INS). This constrains the standard selections rules for magnetic excitations. (2) The INS signatures of magnetic clusters are directly dependent on the state and component that is excited.     

Phonon eigenvectors in Si determined by inelastic neutron scattering

We have determined the eigenvectors of longitudinal phonons with wavevectors in the direction in Si at 12 K from inelastic neutron scattering intensities. The eigenvectors obtained from different model and quantum-mechanical calculations are at variance. Comparison of experimental and theoretical results shows that of the various theoretical predictions the ones from the bond-charge model are in best agreement with experiment. Internal-strain constants from these models and from experiment are compared.     

Raman scattering in ferromagnetic semiconductors under crossed fields

The influence of crossed electric and magnetic fields on the intraband resonant contribution to Raman scattering is discussed. It is shown that in the presence of these fields, the Raman efficiency for one magnon process in ferromagnetic semiconductors exhibits two resonant peaks which are dependent on the ratio βE/Hβ.     

Small-angle neutron spin-flip scattering in ferromagnetic films

This paper reports on the results of reflectometric measurements of anisotropic (Co₆₇Fe₃₁V₂) and almost isotropic (Fe) films prepared by magnetron sputtering. Nonspecular reflections and the corresponding peaks of the intensities of refracted neutrons have been observed for the alloy samples in magnetic fields H ≤ 7 Oe applied in the film plane along the easy magnetization axis. For iron films, angular splitting of the reflected neutron beam becomes observable only at H > 100 Oe and increases with an increase in the magnetic field. A general scheme has been proposed for this small-angle scattering with allowance made for different variants of changes in the Zeeman energy of neutrons. This scheme has allowed us to identify the magnetic structures of Co-Fe films. The magnetization of 0.15-μm-thick films with uniaxial and unidirectional textures leads to the formation of unidirectional textures characterized by different intensity distributions, for which the qualitative differences are retained with an increase in the magnetic field from 7 to 800 Oe. It has been revealed that, for 2.5-μm-thick films with the initial unidirectional texture, the oppositely magnetized states are nonequivalent.     

Elastic and inelastic scattering of electrons by vibrating impurities in semiconductors

Elastic and inelastic scattering of conduction electrons by vibrating ionized impurities in valence semiconductors is investigated. For elastic scattering, the modification of the Brooks-Herring formula arising from impurity vibrations is unimportant for all conceivable electron temperatures and donor concentrations. Similarily, for inelastic (one-phonon) processes, the change in electron-phonon relaxation time (or in electron-lattice coupling constant) arising from vibrations of the ionized centres is entirely negligible.     

Two-photon exchange in deep inelastic scattering

We have measured the contribution of the two-photon exchange amplitude in deep inelastic muon-nucleon scattering. We find, with 95% confidence, that the real part of this amplitude is less than 0.017 of the one photon-exchange amplitude. The range of the 4-momentum transfer covered is 0.5 < Q² < 2.1 (GeV/c)².     

Elastic constants in RbI,determined by inelastic neutron scattering

Long-wavelength acoustic phonons have been studied in the whole (100)-plane of RbI at 295 K by means of inelastic neutron scattering. The raw data have been corrected for resolution effects taking into account the curvature of the dispersion surface and variations of the mode eigenvectors. The shifts of the neutron groups due to these resolution effects are discussed in detail. The analysis of the experimental results gives for the zero sound elastic constantsc ₁₁=28.15±0.5,c ₁₂=3.7±0.5 andc ₄₄=2.85±0.1 10¹⁰ dyn/cm². A comparison with first sound elastic constants taken from ultrasonic measurements yields significant differences between the high and low frequency elastic constantsc ₁₁ andc=(c ₁₁–c ₁₂)/2. The differences calculated from recent theories are in agreement with the experimental results for the elastic constantsc ₁₁,c ₄₄ andc, but not forc ₁₂. The dispersion surface in the (100)-plane is also shown for some out-of-symmetry data and compared with ultrasonic data as well as with theoretical results.Research supported by BMFT     

Giant magnetic moments in ferromagnetic oxide semiconductors

Concentration dependence of the specific magnetic moment of Co-and Fe-doped titanium oxide semiconductors has been studied at room temperature. A sharp increase in the magnetic moment has been found at low concentrations of a magnetic impurity. A giant value of 22.9 μ_B per impurity atom has been detected in TiO₂ with a Co concentration of 0.15 at %, which has never been observed in oxide systems. The giant magnetic moments observed at low impurity concentration are attributed to the polarization of a crystal lattice. Comparison with the literature data indicates that the concentration dependences of magnetization are different in different oxide matrices.     

Unpolarized neutron diffuse scattering from magnetic clusters in nearly and weakly ferromagnetic alloys

It is suggested that the observed unpolarized neutron elastic diffuse magnetic scattering from alloys in the critical concentration region for the onset of ferromagnetism may be usefully considered as the paramagnetic scattering from an assembly of nearly independent magnetic clusters.     

Hydrodynamic effects in bicontinuous microemulsions measured by inelastic neutron scattering

The dynamical properties of bicontinuous microemulsions have been studied with neutron spin echo spectroscopy around length scales corresponding to the correlation peak q₀. Comparison of samples with different contrasts for neutrons shed light on the two modes dominated either by variation of the oil/water difference or surfactant concentration in the hydrodynamic regime. The results have been compared to theoretical predictions of the relaxation rates of bicontinuous microemulsions by Nonomura and Ohta [M. Nonomura, T. Ohta, J. Chem. Phys. 110, 7516 (1999)]. The influence of modification of the surfactant layer bending constants in the microemulsion by addition of homopolymers (polyethylenepropylene: PEP_X and polyethyleneoxide: PEO_X, X=5 kg/mol), dissolved in the oil phase and water, has been investigated.     

Hyperfine interaction in amorphous ferromagnetic cobalt-phosphorous-alloys measured by inelastic scattering of neutrons

The hyperfine interaction at the cobalt nucleus in amorphous ferromagnetic cobalt-phosphorous-alloys CoP _x has been investigated by measuring the inelastic incoherent spin-flip scattering of neutrons. A neutron spectrometer of an extremely high energy resolution of 67 MHz full width at half maximum (FWHM) was used. It was found that the magnetic hyperfine splitting, in first order, is proportional to the magnetic moment of the cobalt atom and that there is a distribution of hyperfine fields of about 50 MHz around a mean value which depends on the phosphorous concentration.