Control of positive and negative magnetoresistance in iron oxide−iron nanocomposite thin films for tunable magnetoelectric nanodevices

The perspective of energy-efficient and tunable functional magnetic nanostructures has triggered research efforts in the fields of voltage control of magnetism and spintronics. We investigate the magnetotransport properties of nanocomposite iron oxide/iron thin films with a nominal iron thickness of 5-50 nm and find a positive magnetoresistance at small thicknesses. The highest magnetoresistance was found for 30 nm Fe with +1.1% at 3 T. This anomalous behavior is attributed to the presence of Fe3O4-Fe nanocomposite regions due to grain boundary oxidation. At the Fe3O4/Fe interfaces, spin-polarized electrons in the magnetite can be scattered and reoriented. A crossover to negative magnetoresistance (−0.11%) is achieved at a larger thickness (>40 nm) when interface scattering effects become negligible as more current flows through the iron layer. Electrolytic gating of this system induces voltage-triggered redox reactions in the Fe3O4 regions and thereby enables voltage-tuning of the magnetoresistance with the locally oxidized regions as the active tuning elements. In the low-magnetic-field region (<1 T), a crossover from positive to negative magnetoresistance is achieved by a voltage change of only 1.72 V. At 3 T, a relative change of magnetoresistance about −45% during reduction was achieved for the 30 nm Fe sample. The present low-voltage approach signifies a step forward to practical and tunable room-temperature magnetoresistance-based nanodevices, which can boost the development of nanoscale and energy-efficient magnetic field sensors with high sensitivity, magnetic memories, and magnetoelectric devices in general

Synthetic, structural, and spectroscopic studies of sterically crowded tin-chalcogen acenaphthenes

The work in this project was supported by the Engineering and Physical Sciences Research Council (EPSRC) and EaStCHEM.A series of sterically encumbered peri-substituted acenaphthenes have been prepared containing chalcogen and tin moieties at the close 5,6-positions (Acenap[SnPh3][ER], Acenap = acenaphthene-5,6-diyl, ER = SPh (1), SePh (2), TePh (3), SEt (4); Acenap[SnPh2Cl][EPh], E = S (5), Se (6); Acenap[SnBu2Cl][ER], ER = SPh(7), SePh (8), SEt (9)). Two geminally bis(peri-substituted) derivatives ({Acenap[SPh2]}2SnX2, X = Cl (10), Ph (11)) have also been prepared, along with the bromo–sulfur derivative Acenap(Br)(SEt) (15). All 11 chalcogen–tin compounds align a Sn–CPh/Sn–Cl bond along the mean acenaphthene plane and position a chalcogen lone pair in close proximity to the electropositive tin center, promoting the formation of a weakly attractive intramolecular donor–acceptor E···Sn–CPh/E···Sn–Cl 3c-4e type interaction. The extent of E→Sn bonding was investigated by X-ray crystallography and solution-state NMR and was found to be more prevalent in triorganotin chlorides 5–9 in comparison with triphenyltin derivatives 1–4. The increased Lewis acidity of the tin center resulting from coordination of a highly electronegative chlorine atom was found to greatly enhance the lp(E)−σ*(Sn–Y) donor–acceptor 3c-4e type interaction, with substantially shorter E–Sn peri distances observed in the solid state for triorganotin chlorides 5–9 (∼75% ∑rvdW) and significant 1J(119Sn,77Se) spin–spin coupling constants (SSCCs) observed for 6 (163 Hz) and 8 (143 Hz) in comparison to that for the triphenyltin derivative 2 (68 Hz). Similar observations were observed for geminally bis(peri-substituted) derivatives 10 and 11.PostprintPeer reviewe

Using internal strain and mass to modulate Dy amp; 8943;Dy coupling and relaxation of magnetization in heterobimetallic metallofullerenes DyM2N C80 and Dy2MN C80 M Sc, Y, La, Lu

Endohedral clusters inside metallofullerenes experience considerable inner strain when the size of the hosting cage is comparably small. This strain can be tuned in mixed metal metallofullerenes by combining metals of different sizes. Here we demonstrate that the internal strain and mass can be used as variables to control Dy amp; 8943;Dy coupling and relaxation of magnetization in Dy metallofullerenes. Mixed metal nitride clusterfullerenes DyxY3 amp; 8722;xN Ih C80 x 0 3 and Dy2LaN Ih C80 combining Dy with diamagnetic rare earth elements, Y and La, were synthesized and characterized by single crystal X ray diffraction, SQUID magnetometry, ab initio calculations, and spectroscopic techniques. DyxY3 amp; 8722;xN clusters showed a planar structure, but the slightly larger size of Dy3 in comparison with that of Y3 resulted in increased elongation of the nitrogen thermal ellipsoid, showing enhancement of the out of plane vibrational amplitude. When Dy was combined with larger La, the Dy2LaN cluster appeared strongly pyramidal with the distance between two nitrogen sites of 1.15 1 , whereas DyLa2N C80 could not be obtained in a separable yield. Magnetic studies revealed that the relaxation of magnetization and blocking temperature of magnetization in the DyM2N C80 series M Sc, Y, Lu correlated with the mass of M, with DySc2N C80 showing the fastest and DyLu2N C80 the slowest relaxation. Ab initio calculations predicted very similar g tensors for Dy3 ground state pseudospin in all studied DyM2N C80 molecules, suggesting that the variation in relaxation is caused by different vibrational spectra of these compounds. In the Dy2MN C80 series M Sc, Y, La, Lu , the magnetic and hysteretic behavior was found to correlate with Dy amp; 8943;Dy coupling, which in turn appears to depend on the size of M3 . Across the Dy2MN C80 series, the energy difference between ferromagnetic and antiferromagnetic states changes from 5.6 cm amp; 8722;1 in Dy2ScN C80 to 3.0 cm amp; 8722;1 in Dy2LuN C80, 1.0 cm amp; 8722;1 in Dy2YN C80, and amp; 8722;0.8 cm amp; 8722;1 in Dy2LaN C80. The coupling of Dy ions suppresses the zero field quantum tunnelling of magnetization but opens new relaxation channels, making the relaxation rate dependent on the coupling strengths. DyY2N C80 and Dy2YN C80 were found to be non luminescent, while the luminescence reported for DyY2N C80 was caused by traces of Y3N C80 and Y2ScN C8