Carrier-induced ferromagnetism in p-Zn1-xMnxTe

We present a systematic study of the ferromagnetic transition induced by the holes in nitrogen doped Zn1-xMnxTe epitaxial layers, with particular emphasis on the values of the Curie-Weiss temperature as a function of the carrier and spin concentrations. The data are obtained from thorough analyses of the results of magnetization, magnetoresistance and spin-dependent Hall effect measurements. The experimental findings compare favorably, without adjustable parameters, with the prediction of the Rudermann-Kittel-Kasuya-Yosida (RKKY) model or its continuous-medium limit, that is, the Zener model, provided that the presence of the competing antiferromagnetic spin-spin superexchange interaction is taken into account, and the complex structure of the valence band is properly incorporated into the calculation of the spin susceptibility of the hole liquid. In general terms, the findings demonstrate how the interplay between the ferromagnetic RKKY interaction, carrier localization, and intrinsic antiferromagnetic superexchange affects the ordering temperature and the saturation value of magnetization in magnetically and electrostatically disordered systems.Comment: 14 pages, 10 figure

Light and electric field control of ferromagnetism in magnetic quantum structures

A strong influence of illumination and electric bias on the Curie temperature and saturation value of the magnetization is demonstrated for semiconductor structures containing a modulation-doped p-type Cd0.96Mn0.04Te quantum well placed in various built-in electric fields. It is shown that both light beam and bias voltage generate an isothermal and reversible cross-over between the paramagnetic and ferromagnetic phases, in the way that is predetermined by the structure design. The observed behavior is in quantitative agreement with the expectations for systems, in which ferromagnetic interactions are mediated by the weakly disordered two-dimensional hole liquid.Comment: 4 pages and 3 figure

Risk factors for pre-term birth in Iraq: a case-control study

BACKGROUND: Preterm birth (PTB)is a major clinical problem associated with perinatal mortality and morbidity. The aim of the present study is to identify risk factors associated with PTB in Mosul, Iraq. METHODS: A case-control study was conducted in Mosul, Iraq, from 1(st )September, 2003 to 28(th )February, 2004. RESULTS: A total of 200 cases of PTB and 200 controls of full-term births were screened and enrolled in the study. Forward logistic regression analysis was used in the analysis. Several significant risk associations between PTB and the following risk factors were identified: poor diet (OR = 4.33), heavy manual work (OR = 1.70), caring for domestic animals (OR = 5.06), urinary tract infection (OR = 2.85), anxiety (OR = 2.16), cervical incompetence (OR = 4.74), multiple pregnancies (OR = 7.51), direct trauma to abdomen (OR = 3.76) and abortion (OR = 6.36). CONCLUSION: The main determinants of PTB in Iraq were low socio-economic status and factors associated with it, such as heavy manual work and caring for domestic animals, in addition to urinary tract infections and poor obstetric history

OPTICALLY DETECTED E.P.R. OF SELF-TRAPPED EXCITONS IN ALKALI FLUORIDES-LUMINESCENCE IDENTIFICATION

La résonance de l'exciton autopiégé dans NaF, LiF et KF a été observée par détection optique. La bande d'émission π issue de l'état triplet a été identifiée et sa durée de vie mesurée. La structure hyperfine observée est en accord avec le modèle décrivant l'exciton autopiégé comme un Vk, ayant capturé un électron. La décomposition à champ magnétique nul de l'état triplet est principalement définie par les interactions dipolaires magnétiques. L'observation d'un croisement de niveaux montre que les sous-niveaux Zeeman ne sont pas en équilibre thermique.The optical-microwave double resonance of the triplet state of the self-trapped exciton has been detected in alkali fluorides. The luminescence originating from this triplet state (π band) has been identified and the corresponding lifetime measured. The values for the hyperfine interaction parameters are consistent with the model of the Vk having trapped an electron. The contribution of the dipole-dipole interaction to the zero field splitting is dominant. An observed level crossing has shown that the triplet sublevels are not in thermal equilibrium

Multiple quantum well exciton Bragg mirrors, tunable by magnetic field

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CENTRES COLORÉS, PROPRIÉTÉS SPECTROSCOPIQUESDÉTECTION OPTIQUE DE LA RÉSONANCE ÉLECTRONIQUE DE L'EXCITON AUTOPIÉGÉ DANS LES HALOGÉNURES ALCALINS ; OBSERVATION D'UN CROISEMENT DE NIVEAUX

La résonance dc l'exciton autopiégé dans KBr, RbBr, NaCl a été observée par détection optique. Dans le cas de KBr, les constantes de l'hamiltonien de spin ont été déterminées. Les spectres de résonance montrent qu'à 1,6 K, l'équilibre de Boltzmann n'est pas atteint. L'ensemble de ces résultats est décrit dans une publication récente et sera seulement brièvement résumé ici. Les résultats obtenus sur KBr sont comparés à ceux prédits dans un modèle simple. L'observation d'un effet de croisement de niveau est décrite.Electron Paramagnetic Resonance of the self trapped exciton was observed in NaCl, RbBr and KBr. The parameters defining the spin hamiltonian were determined for KBr. The appearance of the EPR spectra shows that at low temperature (1.6 K) the populations of the Zeeman sublevels are not in thermal equilibrium. These experimental results are described in a recent publication and they will only be briefly recalled. The parameters determined for KBr are compared to those predicted within a simple model. The observation of a level crossing effect is described

Détection optique de la résonance électronique de l'exciton autopiégé dans les halogénures alcalins ; observation d'un croisement de niveaux

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Oscillator strength transfer from X to X + in a CdTe quantum-well microcavity

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