Zr-Based Heusler Compounds for Biomedical Spintronic Applications

Current advances in microelectronics depend on novel approaches based on the synergistic use of charge and spin dynamics of electrons in multi-functional materials. Such new concepts have already found practical applications in magnetoelectronics or spintronics (e.g., spin valves or nonvolatile memory components). For efficient spintronic devices, it is desirable to have an enhanced spin polarization, that, to work with nearly 100% spin-polarized currents. Since half metallic materials have electrons of unique spin polarization around the Fermi level (finite density of states in only one spin channel), they are promising candidates for use as spin injectors in spintronic devices. Although the Heusler compounds reported in the literature presenting half-metallic ferro/ferrimagnetism are numerous, only a few contain elements with low toxicity, as for example zirconium, being also susceptible of convenient preparation and processing. Therefore, in future, zirconium-based compounds could become a much suitable alternative to the presently known cobalt, iron, chromium, titanium, manganese, or scandium-based half-metallic Heusler compounds, being of interest especially in biomedical spintronic related applications involved in corrosive/active environment

Mössbauer spectral study of the RFe11.5Ta0.5 (R=Tb, Dy, Ho, Er, and Lu) compounds

18 pages, 15 figures, 10 tables.-- PACS number(s): 75.50.Bb, 75.50.Ww, 76.80.+yThe paper presents an iron-57 Mössbauer spectral study of RFe11.5Ta0.5, with R=Tb, Dy, Ho, Er, Lu, and an evaluation of the different contributions to the hyperfine magnetic fields. The Mössbauer spectra have been analyzed with a model that considers both the distribution of the tantalum atoms in the near-neighbor environment of the iron atoms and the relative orientation of the hyperfine field and the principal axis of the electric field gradient. Their possible directions in the ThMn12 structure have been determined from a close examination of the point symmetry of each iron site. A local model for the hyperfine field which enables to determine their components from experimental data, has been developed and a calculation of the lattice dipolar hyperfine field in RFe11.5Ta0.5 has been performed. We have investigated in detail the origin and influence of the contributions to the hyperfine field coming from self 3d polarization, the iron and rare earth transferred fields and the orbital and dipolar hyperfine fields. The iron and rare earth transferred fields have been analyzed for RFe11.5Ta0.5 and other rare earth-iron intermetallic compounds. From this analysis it is shown that the iron transferred fields are different at each crystallographic site, and comparable to the self 3d polarization contributions, and that the rare earth transferred field is mainly originated by the indirect exchange between the rare earth 4f and iron 3d electrons.This work was financed by the MAT 02/166 and MAT 2000/0107/P4-02 MCYT projects (Spanish government). C.P. thanks MCYT for financial Grant No. PN73195091Y.Peer reviewe

Spectroscopic investigations on PVDF-Fe2O3 nanocomposites

Polyvinylidene fluoride-iron oxide (PVDF-Fe2O3) nanocomposites have been obtained my melt mixing of PVDF with Fe2O3 nanoparticles. The interactions between the polymeric matrix and the nanofiller have been investigated by wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, using both red and green excitations (lasers). WAXS, FTIR, and Raman spectra confirm that all samples contain α PVDF as the major crystalline form of the polymeric matrix. Experimental data revealed small changes in the positions of X-ray lines as well as modifications of the width of X-ray lines upon loading by Fe2O3 nanoparticles. FTIR and Raman spectra are dominated by the lines of the polymeric matrix. Within the experimental errors, the positions of Raman lines are not affected by the wavelength of the incoming electromagnetic radiation, although they are sensitive to the strain of the polymeric matrix induced by addition of the nanofiller. The loading of the polymeric matrix with nanoparticles stretches the macromolecular chains, affecting their vibrational spectra (FTIR and Raman). A complex dependence of the positions of some Raman and FTIR lines on the loading with Fe2O3 is reported. The manuscript provides a detailed analysis of the effects of nanofiller on the position of WAXS, FTIR, and Raman lines

Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications

Multifunctional magnetic nanocomposites are among those heterogeneous nanosized systems where at least one phase component is magnetic and can act as an intermediate of either the actuation or the response of the overall system. The main advantage of heterogeneous nanosystems is the possibility of combining and inter-influencing the electronic properties of constituent interfaced nanophases. Consequently, unique physico-chemical properties of the hybrid materials of interest in various applications can be obtained. This Special Issue of Nanomaterials highlights the most advanced processing and characterization tools of some multifunctional magnetic nanocomposites and heterogeneous systems of interest in various applications, from biomedicine to sensoristics and energy-saving materials

Shaping distinct magnetic interactions in molecular compounds

Oxalates containing various 3d transitional elements and positive NH 4 or negative OH groups were newly synthesized. Each above-mentioned component has directly influenced the structure, the electronic or interaction properties, while some unexpected behaviors were revealed by various magnetic and Mssbauer measurements. The main magnetic parameters, the long-range anti-ferromagnetic couplings observed at very low temperature and, particularly the uncompensated moment are discussed in detail. The induced lower spin states for bivalent ions and especially the anti-parallel arrangement of the spins belonging to trivalent and bivalent iron inside the molecule are also emphasized. © 2010 Elsevier B.V. All rights reserved.The financial support of CNCSIS-UEFISCSU via contract 235/2007 of ‘‘IDEI’’ Romanian National Program and, respectively, MINCYT Spain projectMAT08/1077 are acknowledged, firstly and deeply.Peer Reviewe

Relationship between the Formation of Magnetic Clusters and Hexagonal Phase of Gold Matrix in AuxFe1−x Nanophase Thin Films

AuxFe1−x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, Superconducting Quantum Interference Device magnetometry and Conversion Electron Mössbauer Spectroscopy. It was proven that depending on the preparation conditions, different configurations of defect α-Fe magnetic clusters, i.e., randomly distributed or auto-assembled in lamellar or filiform configurations, can be formed in the Au matrix. A close relationship between the Fe clustering process and the type of the crystalline structure of the Au matrix was underlined, with the stabilization of a hexagonal phase at a composition close to 70 at. % of Au and at optimal thickness. Due to different types of inter-cluster magnetic interactions and spin anisotropies, different types of magnetic order from 2D Ising type to 3D Heisenberg type, as well as superparamagnetic behavior of non-interacting Fe clusters of similar average size, were evidenced

Influence of Thickness on the Magnetic and Magnetotransport Properties of Epitaxial La0.7Sr0.3MnO3 Films Deposited on STO (0 0 1)

Epitaxial La0.7Sr0.3MnO3 films with different thicknesses (9–90 nm) were deposited on SrTiO3 (0 0 1) substrates by pulsed laser deposition. The films have been investigated with respect to morpho-structural, magnetic, and magneto-transport properties, which have been proven to be thickness dependent. Magnetic contributions with different switching mechanisms were evidenced, depending on the perovskite film thickness. The Curie temperature increases with the film thickness. In addition, colossal magnetoresistance effects of up to 29% above room temperature were evidenced and discussed in respect to the magnetic behavior and film thickness

Magnetism and magnetoresistance of single Ni–Cu alloy nanowires

Arrays of magnetic Ni–Cu alloy nanowires with different compositions were prepared by a template-replication technique using electrochemical deposition into polycarbonate nanoporous membranes. Photolithography was employed for obtaining interdigitated metallic electrode systems of Ti/Au onto SiO2/Si substrates and subsequent electron beam lithography was used for contacting single nanowires in order to investigate their galvano-magnetic properties. The results of the magnetoresistance measurements made on single Ni–Cu alloy nanowires of different compositions have been reported and discussed in detail. A direct methodology for transforming the magnetoresistance data into the corresponding magnetic hysteresis loops was proposed, opening new possibilities for an easy magnetic investigation of single magnetic nanowires in the peculiar cases of Stoner–Wohlfarth-like magnetization reversal mechanisms. The magnetic parameters of single Ni–Cu nanowires of different Ni content have been estimated and discussed by the interpretation of the as derived magnetic hysteresis loops via micromagnetic modeling. It has been theoretically proven that the proposed methodology can be applied over a large range of nanowire diameters if the measurement geometry is suitably chosen

The influences of the packing ligand on spin state and magnetic interactions in new oxalates with 3d-transition metals.

3 figures, 1 table.Two new hetero tri-nuclear oxalates (NH4)8[Fe2Co(C2O4)8]·6H2O and [Fe2Co(C2O4)2(OH)4]·2H2O have been synthesized. The compound presented opposite behaviour in ac-susceptibility measurements, different frustration level and spin–orbit coupling in magnetization ones. The Mössbauer approach pointed to local interactions governed by metal-oxalate strongly coupled unit. The data were interpreted in terms of role of positive (NH4) or negative (OH) bridging ligands on general magnetic properties.Peer reviewe