High-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)(3), with 1,2-hexadecanediol in the presence of oleic acid and oleylamine leads to monodisperse magnetite (Fe(3)O(4)) nanoparticles. Similarly, reaction of Fe(acac)(3) and Co(acac)(2) or Mn(acac)(2) with the same diol results in monodisperse CoFe(2)O(4) or MnFe(2)O(4) nanoparticles. Particle diameter can be tuned from 3 to 20 nm by varying reaction conditions or by seed-mediated growth. The as-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM, SAED, and XRD. Further, Fe(3)O(4) can be oxidized to Fe(2)O(3), as evidenced by XRD, NEXAFS spectroscopy, and SQUID magnetometry. The hydrophobic nanoparticles can be transformed into hydrophilic ones by adding bipolar surfactants, and aqueous nanoparticle dispersion is readily made. These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.

Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.

Dumbbell-like Au-Fe(3)O(4) nanoparticles are synthesized using decomposition of Fe(CO)(5) on the surface of the Au nanoparticles followed by oxidation in 1-octadecene solvent. The size of the particles is tuned from 2 to 8 nm for Au and 4 nm to 20 nm for Fe(3)O(4). The particles show the characteristic surface plasmon absorption of Au and the magnetic properties of Fe(3)O(4) that are affected by the interactions between Au and Fe(3)O(4). The dumbbell is formed through epitaxial growth of iron oxide on the Au seeds, and the growth can be affected by the polarity of the solvent, as the use of diphenyl ether results in flower-like Au-Fe(3)O(4) nanoparticles.

Dynamic state switching in nonlinear multiferroic cantilevers Appl. Phys. Lett. 101, 043506 (2012) Nanomagnetism of cobalt ferrite-based spin filters probed by spin-polarized tunneling Appl. Phys. Lett. 101, 042409 (2012) Magnetic Schottky diode exploiting spin polarized transport in Co/p-Si heterostructure Appl. Phys. Lett. 100, 262402 (2012) Concepts and steps for the realization of a new domain wall based giant magnetoresistance nanowire device: From the available 24 multiturn counter to a 212 turn counter Exchange biased magnetic tunnel junction ͑MTJ͒ structures are shown to have useful properties for forming magnetic memory storage elements in a novel cross-point architecture. MTJ elements have been developed which exhibit very large magnetoresistive ͑MR͒ values exceeding 40% at room temperature, with specific resistance values ranging down to as little as ϳ60 ⍀͑m͒ 2 , and with MR values enhanced by moderate thermal treatments. Large MR values are observed in magnetic elements with areas as small as 0.17 ͑m͒ 2 . The magnetic field dependent current-voltage characteristics of an MTJ element integrated with a silicon diode are analyzed to extract the MR properties of the MTJ element itself.