The interfacial regimes of cobalt/pentacene/cobalt (Co/Pc/Co) trilayers were emulated through the ultrathin pentacene/cobalt (Pc/Co) and cobalt/pentacene (Co/Pc) bilayers. Employing the magneto-optical Kerr effect (MOKE) measurement, we found the coercivity of Co bottom film in a thickness of 3.4 nm experienced a slight reduction upon the adsorption of Pc molecules. For the bilayers prepared with reversed order of deposition, the Co film deposited on a 6.4 nm Pc layer showed no observable ferromagnetic order at room temperature until its thickness reached 3 nm. After the onset of magnetic order, the x-ray images acquired on Pc/Co revealed a complicated magnetization patterns comparing to those observed on Co/Pc bilayers. Because the spin-polarized carriers will interact with the environment along their transport path, the presence of a non-magnetic layer and the occurrence of complicated domain structures suggested the spin-polarized carriers would experience a greater disturbance on their spin coherence when crossing the Pc/Co interface.

We have proposed a spin quantum cross structure (SQCS) device as a candidate beyond CMOS. The SQCS device consists of two ferromagnetic metal thin films with their edges crossed, and sandwiches a few atoms or molecules. In this work, the spin dependent transport formula has been derived for SQCS devices with collinear ferromagnetic electrodes within the framework of the Anderson Hamiltonian. Also, the calculation of the magnetoresistance (MR) ratio has been done as a function of renormalized transfer matrices including magnetostriction effects and the other effects phenomenologically. It is shown that the MR ratio can be controlled by changing the renormalized coupling constants. The MR ratio is represented by a new formula. Also, we have realized an SQCS device with Ni magnetic thin-film electrodes, sandwiching poly (3-hexylthiophene) (P3HT): 6, 6-phenyl-C61-butyric acid methyl ester (PCBM) organic molecules between both the electrodes. The current-voltage characteristics of SQCS devices were measured by a four-terminal method and agree well with the theoretical results, quantitatively.

We report on metal organic chemical vapor deposition growth of GaMnN/p-GaN/n-GaN multilayer structures and manipulation of room temperature (RT) ferromagnetism (FM) in a GaMnN layer. The GaMnN layer was grown on top of a n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. Ms was almost doubled after annealing demonstrating that the FM observed in GaMnN film is carrier-mediated. To control the hole concentration of the p-GaN layer by depletion, GaMnN/p-GaN/n-GaN multilayer structures of different p-GaN thickness (Xp) were grown on sapphire substrates. We have demonstrated that the FM depends on the Xp and the applied bias to the GaN p-n junction. The FM of these multilayer is independent on the top GaMnN layer thickness (tGaMnN) for tGaMnN >200 nm and decreases for tGaMnN < 200 nm. Thus the room temperature FM of GaMnN i-p-n structure can also be controlled by changing Xp and tGaMnN in the GaMnN i-p-n structures.

Fe0.1Sc0.9N with a thickness of ˜ 380 nm was grown on top of a ScN(001) buffer layer of ˜ 50 nm, grown on MgO(001) substrate by radio-frequency N-plasma molecular beam epitaxy (rf-MBE). The buffer layer was grown at TS ˜ 800 oC, whereas the Fe0.1Sc0.9N film was grown at TS ˜ 420 oC. In-situ reflection high-energy electron diffraction measurements show that the Fe0.1Sc0.9N film growth starts with a combination of spotty and streaky pattern [indicative of a combination of smooth and rough surface]. After ˜ 10 minutes of growth, the pattern converts to a spotty one [indicative of a rough surface]. Towards the end of the Fe0.1Sc0.9N film growth, the spotty patterns transform into even spottier, but also ring-like indicating a polycrystalline behavior. Superconducting quantum interference device magnetic measurements show a ferromagnetic to paramagnetic transition of TC ˜ 370 – 380 K. We calculated a magnetic moment per atom of μ(Fe0.1Sc0.9N) = 0.037 Bohr magneton/ Mn-atom. Based on the carrier concentration measurements (nS(Fe0.1Sc0.9N) = 2.086 × 1019 /cm3), we find that iron behaves as an acceptor. Comparisons are made with similar MnScN (001)/ScN(001)/MgO(001) system.

The interface problems in nanomaterial based electronics play important roles. We have learned that the nanocontact, due to its reduced contact area, could give a high electrical contact resistance and a nonlinear current-voltage behavior though the specific contact resistance is in the same order of magnitude as that of macroscopic contacts. Through the current-voltage and temperature behaviors, the nanocontact properties could be categorized into Ohmic and Schottky types. The electrical properties of the nanowire based two-probe devices could be rationalized as two Ohmic contacts, one Ohmic and one Schottky contacts, and two back-to-back Schottky contacts. Moreover, the nanocontact could be treated as a one-dimensional disordered electron system for further studies. After the intrinsic nanowire and contact resistances are separated from each other, the electron transport and the carrier concentration of native doping in ZnO and InP nanowires can be determined. The nanowires are determined to have low carrier concentrations, implying a high sensitivity to light and gas. The contact and nanowire dominated two-probe devices are exposed to light and gas to identify the contact effects. In addition to the inorganic nanowires, the organic nanomaterials, the HCl-doped polyaniline nanofibers, can be analyzed by using the same approach. The dielectrophoresis technique is implemented to position nanofibers into an electron-beam lithographically patterned nanogap. To shine the electron-beam on contact areas, the organic/inorganic nanocontact resistance is reduced so as to probe the intrinsic electrical property of a single polyaniline nanofiber.

We present a detailed study of the angular dependence of the magnetization reversal at room temperature of well characterized epitaxial La0.7Sr0.3MnO3 (001) thin films grown onto SrTiO3 (001) vicinal substrates. The step edges at the substrate surface promote a topological modulation of the films along the step direction, breaking the four-fold magneto crystalline symmetry and favoring a two-fold magnetic anisotropy term. The competition between the biaxial and uniaxial anisotropy is depicted within the framework of the current theory, resulting in a vanishing biaxial contribution. The films hence show the magnetization easy (hard) direction parallel (perpendicular) to the steps direction. The thickness-dependent of both anisotropy and magnetization reversal are discussed in terms of topographic changes.

The past decade has witnessed a great interest in single molecule magnets (SMM) especially those based on manganese such as Mn12-acetate due to their potential applications in ultrahigh density data storage and quantum computing devices. The focus so far has been in finding different derivatives of Mn or other complexes based on transition elements in order to raise the blocking temperature of single-molecule magnets (SMMs). Herein we propose a fundamentally new approach of generating new category of SMMs through formation of composite structures by binding SMMs on to nanoparticles. In this report, we present the synthesis and characterization of single molecular magnet - gold nanoparticle composite- Mn12-cysteinate functionalized gold nanoparticles.

Electronic and magnetic properties of small Co-O atomic clusters (“quantum wires”) have been studied in the framework of the Hartree-Fock (HF) method. The obtained results indicate that non-stoichiometric Co - O molecules with more than two O atoms possess at least one remarkably stretchable O-O bond that may facilitate significant re-construction of such molecules to larger structures. This re-construction may result in energetically favorable spin re-alignment in “antiferromagnetic” HF singlet Co-O molecules converting the singlets to larger “ferromagnetic” HF triplets and pentets. Such a spin re-alignment is energetically favorable, and may happen at the antiferromagnet-ferromagnet interface in “critical” core (Co) – shell (CoO) exchange-biased nanoclusters, providing for minimization of the surface energy, and leading to a loss of exchange bias. The obtained results are in agreement with available experimental and computational data.

Perpendicularly magnetized magnetic tunnel junctions (pMTJ) using Co based multilayers as free and reference layers have been optimized for perpendicular magnetic anisotropy (PMA) and high tunneling magnetoresistance (TMR). The effect of seed layers, Co thickness and Co/Ni thickness ratio on the anisotropy of these multilayer films has been studied. Intermixing of these multilayers was analyzed by local electrode atom probe (LEAP). The effect of Co thickness, Pd thickness and number of Co/Pd bilayers on the anisotropy and coercivity of the [Co/Pd]n multilayer films have been studied for both free and reference layers. The magnetic behavior of these PMA systems was studied by alternating gradient magnetometer. CoFeB/MgO/CoFeB trilayers sandwiched between the PMA multilayer material systems were studied. The transport properties of the patterned MTJ stacks were measured by PPMS from 10K to 400 K. A maximum TMR of 10% at 10K (5-10% at 300 K) was obtained for these perpendicular MTJ’s (pMTJ), regardless of whether they were magnetically annealed for MgO-CoFeB crystallization or not, indicating that the fcc-bcc-fcc transitions from the fcc multilayers to the bcc CoFeB/MgO/CoFeB do not promote the “giant MgO TMR effect” caused by symmetry filtering.