Spin-dependent transport properties of Fe3O4/MoS2/Fe3O4 junctions

Magnetite is a half-metal with a high Curie temperature of 858 K, making it a promising candidate for magnetic tunnel junctions (MTJs). Yet, initial efforts to exploit its half metallic nature in Fe3O4/ MgO/Fe3O4 MTJ structures have been far from promising. Finding suitable barrier layer materials, which keep the half metallic nature of Fe3O4 at the interface between Fe3O4 layers and barrier layer, is one of main challenges in this field. Two-dimensional (2D) materials may be good candidates for this purpose. Molybdenum disulfide (MoS2) is a transition metal dichalcogenide (TMD) semiconductor with distinctive electronic, optical, and catalytic properties. Here, we show based on the first principle calculations that Fe3O4 keeps a nearly fully spin polarized electron band at the interface between MoS2 and Fe3O4. We also present the first attempt to fabricate the Fe3O4/MoS2/Fe3O4 MTJs. A clear tunneling magnetoresistance (TMR) signal was observed below 200 K. Thus, our experimental and theoretical studies indicate that MoS2 can be a good barrier material for Fe3O4 based MTJs.Our calculations also indicate that junctions incorporating monolayer or bilayer MoS2 are metallic

Step-induced defects in thin films and the effect on their electrical and magnetic properties

THESIS 11223This thesis investigates step-induced defects in thin films and their effect on the electrical and magnetic properties. Stepped epitaxial Fe3O4 thin films with different thickness were fabricated and their magnetic properties were investigated. The magnetization measurements suggest that the steps induce an additional anisotropy, which has an easy axis perpendicular to steps and the hard axis along the steps. In addition, electrical analysis of a Fe3O4 film grown on stepped SrTiO3 substrate revealed anisotropic resistive switching. When the current was directed parallel to the step-edge direction, lower voltages were required to switch to the lower conducting state than the case where current was perpendicular to the step-edges. This is attributed to the high density of antiphase boundaries present at step edges. In order to control defect densities, a thorough study was carried out to control periodicity and height of the vicinal MgO (100) substrates which is instigated by annealing them at high temperature in air. Furthermore, transport measurements on trilayer graphene synthesized on vicinal cubic-SiC(001), clearly demonstrate that the self-aligned periodic nanodomain boundaries (NBs) induce a charge transport gap

Magnetic and electronic properties of PtSe2 thin film

Two-dimensional (2D) materials with single or few atomic layers have attracted significant attention from the scientific community due to their potential transport physics and prospects for technological applications. A variety of 2D materials beyond graphene with different bandgaps have been synthesized in recent years. One of them is platinum diselenide (PtSe2) with the bandgap energy of 1.2 eV at one monolayer. However, the low throughput synthesis of high quality 2D thin films has thus far hindered the development of devices. The methods of molecular beam epitaxy (MBE) and chemical vapor deposition (CVD) have been used to achieve large-scale fabrication of PtSe2 films, which were fabricated from Pt thin films with different thickness through selenization process. We have grown Fe3O4 on MgO substrate by MBE system in order to fabricate even better epitaxial Pt thin films. After the fabrication of PtSe2 on Fe3O4/MgO, the electronic and magnetic properties of the interface between two epitaxial grown thin films of platinum diselenide and magnetite have been studied

Enhanced Shubnikov–De Haas Oscillation in Nitrogen-Doped Graphene

N-doped graphene displays many interesting properties compared with pristine graphene, which makes it a potential candidate in many applications. Here, we report that the Shubnikov–de Haas (SdH) oscillation effect in graphene can be enhanced by N-doping. We show that the amplitude of the SdH oscillation increases with N-doping and reaches around 5k Ω under a field of 14 T at 10 K for highly N-doped graphene, which is over 1 order of magnitude larger than the value found for pristine graphene devices with the same geometry. Moreover, in contrast to the well-established standard Lifshitz–Kosevich theory, the amplitude of the SdH oscillation decreases linearly with increasing temperature and persists up to a temperature of 150 K. Our results also show that the magnetoresistance (MR) in N-doped graphene increases with increasing temperature. Our results may be useful for the application of N-doped graphene in magnetic devices

Transport Gap Opening and High On Off Current Ratio in Trilayer Graphene with Self Aligned Nanodomain Boundaries

Trilayer graphene exhibits exceptional electronic properties that are of interest both for fundamental science and for technological applications. The ability to achieve a high on off current ratio is the central question in this field. Here, we propose a simple method to achieve a current on off ratio of 104 by opening a transport gap in Bernal stacked trilayer graphene. We synthesized Bernal stacked trilayer graphene with self aligned periodic nanodomain boundaries NBs on the technologically relevant vicinal cubic SiC 001 substrate and performed electrical measurements. Our low temperature transport measurements clearly demonstrate that the self aligned periodic NBs can induce a charge transport gap greater than 1.3 eV. More remarkably, the transport gap of amp; 8764;0.4 eV persists even at 100 K. Our results show the feasibility of creating new electronic nanostructures with high on off current ratios using graphene on cubic Si