Bulklike behavior of magnetoelasticity in epitaxial Fe1-xGax thin films

Bulk Fe1-xGax alloys present a strong sensitivity of the magnetostrictive properties with Ga content with maximum magnetostriction near x=0.19. Here, we present magnetoelastic coefficients measured by the cantilever method on Fe1-xGax thin films grown by molecular beam epitaxy on GaAs(001). We find that Ga-dependent magnetoelastic coefficients in nanometer thin films are comparable in magnitude to the respective bulk values. Moreover, we compare thin films with a tetragonal structure due to a slightly preferential alignment of Ga pairs along the growth direction with and a cubic structure. It turns out that magnetoelastic coefficients are unaffected by a preferential alignment of Ga pairs along the growth direction.Fil: Barturen, Mariana. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Universidad Argentina de la Empresa; Argentina. Université Pierre et Marie Curie; Francia. Centre National de la Recherche Scientifique; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sander, D.. Max Planck Institute For Microstructure Physics; AlemaniaFil: Milano, Julian. Centre National de la Recherche Scientifique; Francia. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Premper, J.. Max Planck Institute For Microstructure Physics; AlemaniaFil: Helman, Christian. Comisión Nacional de Energía Atómica; ArgentinaFil: Eddrief, M.. Universite de Paris VI. Institut des Nanosciences de Paris; FranciaFil: Kirschner, J.. Max Planck Institute For Microstructure Physics; AlemaniaFil: Marangolo, M.. Universite de Paris VI. Institut des Nanosciences de Paris; Franci

Hole spin polarization in GaAlAs:Mn structures

A self-consistent calculation of the electronic properties of GaAlAs:Mn magnetic semiconductor quantum well structures is performed including the Hartree term and the sp-d exchange interaction with the Mn magnetic moments. The spin polarization density is obtained for several structure configurations. Available experimental results are compared with theory.Comment: 4 page

Thermal effects on atomic friction

We model friction acting on the tip of an atomic force microscope as it is dragged across a surface at non-zero temperatures. We find that stick-slip motion occurs and that the average frictional force follows $|\ln v|^{2/3}$, where $v$ is the tip velocity. This compares well to recent experimental work (Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all microscopic parameters. We calculate the scaled form of the average frictional force's dependence on both temperature and tip speed as well as the form of the friction-force distribution function.Comment: Accepted for publication, Physical Review Letter

Spin flip scattering in magnetic junctions

Processes which flip the spin of an electron tunneling in a junction made up of magnetic electrodes are studied. It is found that: i) Magnetic impurities give a contribution which increases the resistance and lowers the magnetoresistance, which saturates at low temperatures. The conductance increases at high fields. ii) Magnon assisted tunneling reduces the magnetoresistance as $T^{3/2}$, and leads to a non ohmic contribution to the resistance which goes as $V^{3/2}$, iii) Surface antiferromagnetic magnons, which may appear if the interface has different magnetic properties from the bulk, gives rise to $T^2$ and $V^2$ contributions to the magnetoresistance and resistance, respectively, and, iv) Coulomb blockade effects may enhance the magnetoresistance, when transport is dominated by cotunneling processes.Comment: 5 page

Nonequilibrium spin distribution in single-electron transistor

Single-electron transistor with ferromagnetic outer electrodes and nonmagnetic island is studied theoretically. Nonequilibrium electron spin distribution in the island is caused by tunneling current. The dependencies of the magnetoresistance ratio $\delta$ on the bias and gate voltages show the dips which are directly related to the induced separation of Fermi levels for electrons with different spins. Inside a dip $\delta$ can become negative.Comment: 11 pages, 2 eps figure

Nanosized Sodium-Doped Lanthanum Manganites: Role of the Synthetic Route on their Physical Properties

In this paper we present the results of the synthesis and characterisation of nanocrystalline La1-xNaxMnO3+delta samples. Two synthetic routes were employed: polyacrylamide-based sol-gel and propellant synthesis. Pure, single phase materials were obtained with grain size around 35 nm for the sol-gel samples and around 55 nm for the propellant ones, which moreover present a more broaden grain size distribution. For both series a superparamagnetic behaviour was evidenced by means of magnetisation and EPR measurements with peculiar features ascribable to the different grain sizes and morphology. Preliminary magnetoresistivity measurements show enhanced low-field (< 1 T) magnetoresistance values which suggest an interesting applicative use of these manganites.Comment: 31 Pages 10 Figures to appear in Chem. Mate

Indirect exchange in GaMnAs bilayers via spin-polarized inhomogeneous hole gas: Monte Carlo simulation

The magnetic order resulting from an indirect exchange between magnetic moments provided by spin-polarized hole gas in the metallic phase of a GaMnAs double layer structure is studied via Monte Carlo simulation. The coupling mechanism involves a perturbative calculation in second order of the interaction between the magnetic moments and carriers (holes). We take into account a possible polarization of the hole gas due to the existence of an average magnetization in the magnetic layers, establishing, in this way, a self-consistency between the magnetic order and the electronic structure. That interaction leads to an internal ferromagnetic order inside each layer, and a parallel arrangement between their magnetizations, even in the case of thin layers. This fact is analyzed in terms of the inter- and intra-layer interactions.Comment: 17 pages and 14 figure

Annotated bibliography of research in the teaching of English

The committee reviews important research works in the teaching of English that have been published in the last year. Committee members include Richard Beach, Martha Bigelow, Martine Braaksma, Deborah Dillon, Jessie Dockter, Lee Galda, Lori Helman, Tanja Janssen, Karen Jorgensen, Richa Kapoor, Lauren Liang, Bic Ngo, David O’Brien, Mistilina Sato, and Cassie Scharber