Formation of spin-polarons in the ferromagnetic Kondo lattice model away from half-filling.

Even though realistic one-dimensional experiments in the field of half-metallic semiconductors are not at hand yet, we are interested in the underlying fundamental physics. In this regard we study a one-dimensional ferromagnetic Kondo lattice model, a model in which a conduction band is coupled ferromagnetically to a background of localized d moments with coupling constant J(H), and investigate the T = 0 phase diagram as a function of the antiferromagnetic interaction J between the localized moments and the band-filling n, since it has been observed that doping of the compounds has led to formation of magnetic domains. We explore the spin-polaron formation by looking at the nearest-neighbour correlation functions in the spin and charge regimes for which we use the density matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems.

Magneto-elastic phase transitions in one-dimensional systems.

The magneto-elastic phase diagram in one-dimensional systems relating to the interplay between magnetism and lattice distortion is studied in a double-exchange and super-exchange model considering classical localized spins and the limit of large Hund's coupling. At low super-exchange interaction energy, a phase transition occurs between electron-full ferromagnetic distorted and electron-empty antiferromagnetic undistorted phases via phase separation. In this case, all electrons and lattice distortions are found within the ferromagnetic domain. For higher super-exchange interaction energy, phase separations consisting of two- or three-site distorted independent magnetic polarons separated by electron-empty undistorted antiferromagnetic links are obtained. In this regime, each polaron contains an electron, leading to a Wigner crystallization. The lattice distortion and charge distribution inside the polarons are also calculated.

The effect of Coulomb interaction at ferromagnetic-paramagnetic metallic perovskite junctions.

We study the effect of Coulomb interactions in transition metal oxide junctions. In this paper we analyze charge transfer at the interface of a three layer ferromagnetic-paramagnetic-ferromagnetic metallic oxide system. We choose a charge model considering a few atomic planes within each layer and obtain results for the magnetic coupling between the ferromagnetic layers. For large numbers of planes in the paramagnetic spacer we find that the coupling oscillates with the same period as in Ruderman-Kittel-Kasuya-Yoshida (RKKY) theory but the amplitude is sensitive to the Coulomb energy. At small spacer thickness however, large differences may appear as a function of the number of electrons per atom in the ferromagnetic and paramagnetic materials, the dielectric constant at each component, and the charge defects at the interface plane, emphasizing the effects of charge transfer.

Anomalous Josephson current in junctions with spin polarizing quantum point contacts.

We consider a ballistic Josephson junction with a quantum point contact in a two-dimensional electron gas with Rashba spin-orbit coupling. The point contact acts as a spin filter when embedded in a circuit with normal electrodes. We show that with an in-plane external magnetic field an anomalous supercurrent appears even for zero phase difference between the superconducting electrodes. In addition, the external field induces large critical current asymmetries between the two flow directions, leading to supercurrent rectifying effects.

Spin and charge ordering in three-leg ladders in oxyborates.

We study the spin ordering within the three-leg ladders present in the oxyborate Fe3O2BO3 consisting of localized classical spins interacting with conduction electrons (one electron per rung). We also consider the competition with antiferromagnetic superexchange interactions to determine the magnetic phase diagram. Besides a ferromagnetic phase we find (i) a phase with ferromagnetic rungs ordered antiferromagnetically and (ii) a zigzag canted spin ordering along the legs. We also determine the induced charge ordering within the different phases and the interplay with lattice instability. Our model is discussed in connection with the lattice dimerization transition observed in this system, emphasizing the role of the magnetic structure.

Spin order in one-dimensional Kondo and Hund lattices.

We study numerically the one-dimensional Kondo and Hund lattices consisting of localized spins interacting antiferromagnetically or ferromagnetically with the itinerant electrons, respectively. Using the density-matrix renormalization group we find, for both models and in the small coupling regime, the existence of new magnetic phases where the local spins order forming ferromagnetic islands coupled antiferromagnetically. Furthermore, by increasing the interaction parameter |J| we find that this order evolves toward the ferromagnetic regime through a spiral-like phase with longer characteristic wavelengths. These results shed new light on the zero temperature magnetic phase diagram for these models.

New type of charge and magnetic order in the ferromagnetic kondo lattice

We study numerically the one dimensional ferromagnetic Kondo lattice, a model widely used to describe nickel and manganese perovskites. By including a nearest-neighbor Coulomb interaction ( V) and a superexchange interaction between the localized moments ( K), we obtain the phase diagram in parameter space for several dopings at T = 0. Because of the competition between double and superexchange, we find a region where the formation of magnetic polarons induces a charge-ordered state which survives also for V = 0. This mechanism should be taken into account in theories of charge ordering involving spin degrees of freedom.

Occupational exposures estimated by means of job exposure matrices in relation to lung function in the PAARC survey.

OBJECTIVES: The aim of this analysis of the French Cooperative PAARC (Pollution Atmosphérique et Affections Respiratoires Chroniques) survey, was to test whether occupational exposures to dusts, gases, or chemical fumes or to specific hazards, estimated by job exposure matrices, were related to a decrease in forced expiratory volume in one second (FEV1). METHODS: The most recent occupation was recorded in adults, aged 25-59, from non-manual worker households. Analysis was restricted to 10,046 subjects whose occupation was encountered at least 10 times in the study and who performed good FEV1 tracings. From occupational title, exposures to dusts, gases, and chemical fumes, and to specific hazards were classified in three categories (no, low, and high) with a British, a French, and an Italian job exposure matrix. Specific hazards were analysed for the British and French job exposure matrices for the same 42 specific dusts, gases, and chemical fumes. To limit spurious associations, a selection of seven hazard groups and 12 specific hazards was set before the start of the analysis. Based on the consistency of the relations according to sex and the British and French job exposure matrices, associations of age, height, city, and smoking adjusted FEV1 score with occupational exposures were classified as very likely, possible, or unlikely. RESULTS: For the three job exposure matrices and both sexes clear exposure-response relations between the level of exposure to dusts, gases, and chemical fumes, and a decrease in FEV1 were found. Associations with FEV1 were classified as very likely for known hazards such as organic dusts and textile dusts, and not previously recognised hazards such as polycyclic aromatic hydrocarbons (PAHs) and detergents, and as possible for solvents, waxes and polishes, and diesel fumes. Associations found for PAHs and solvents were confirmed by the Italian job exposure matrix. Associations remained significant in women, but not in men, after adjustment for educational level. CONCLUSIONS: Hypotheses have been generated for exposure to detergents, PAHs, and solvents, but they need to be interpreted with caution before replication. Significant associations found for known risk factors with a decrease in FEV1 are arguments for the validity of the matrices. Despite the expected limitations of job exposure matrices, these results encourage further work to improve exposure assessment by job exposure matrices.