Lorentz TEM characterisation of magnetic and physical structure of nanostructure magnetic thin films

The work presented in this thesis is an investigation which aims to quantitatively characterise the physical microstructure, magnetic structure and micromagnetic behaviour of nanostructured thin films for magnetic recording and spintronics application. The nanostructures in the present work involve continuous and patterned thin films. Chapters 1, 2, and 3 present the overview backgrounds directly relevant to the work. Chapter 4 focuses on vortex structure in magnetic nanodots. The results confirm that the behaviour of the vortex can be modified by changing the edge geometry of the dots. It is demonstrated a practical method to determine the out-of-plane component of the vortex core with high accuracy and speed. Additionally in-plane curling magnetisation of the vortex is also mapped by reconstructing the electron phase using the transport-of-intensity equation. However this method is susceptible to spurious low spatial frequency and this aspect is explored to show limitations of the method. Chapter 5 deals with the characterisation of magnetic structure in nanoconstrictions intended to trap domain walls (DWs) in the nanoconstrictions. A structure was fabricated with two micron-sized pads as the sources for creation of DWs. A DW can be driven to be pinned at the nanoconstriction resulting in a change of magnetoresistance due to the contribution of the DW to the resistance of the device. The magnetisation configuration around the constriction is studied during the reversal process. It is apparent that that understanding the magnetisation rotation around the constriction and into the pads is the key to the magnetoresistance measurements and the DW resistance is part of this process. Evidences of DW compression at the nanoconstriction were noted. In Chapter 6 the investigation of the physical structure and micromagnetism of CoIr film is described. A hexagonal crystal structure with a [0001] texture normal to the film plane was characterised. Weak anisotropy is observed in the film denoted by a complex reversal on the hard axis due to incoherent rotation of magnetic moments. The film exhibits typical soft magnetic behaviour it merits compared to other soft materials are discussed in light of the results obtained here. Chapter 7 concludes with a discussion of the outcomes of the present thesis. Additionally possible directions for future research in topics discussed in this thesis are proposed

Biology and glyphosate resistance in Chloris truncata (windmill grass) and Chloris virgata (feathertop Rhodes grass) in southern Australia

Chloris truncata and C. virgata, which are major weeds in cotton and grain crops in the sub-tropical region of Australia, have recently emerged as potential weeds of the future in southern Australia. Glyphosate, an inhibitor of 5-enolpyruvylshikimate-3- phosphate synthase (EPSPS), is the most widely used non-selective post-emergence herbicide globally. As a result of over-reliance on glyphosate combined with dominance of reduced tillage systems for weed control, glyphosate-resistant populations of C. truncata have already been reported in Australia. C. virgata is also considered hard to kill with glyphosate, but resistance has not been reported so far in the literature. Studies on growth, development and seed biology of C. truncata and C. virgata were conducted to better understand the biology of these emerging weed species. Under field conditions, C. truncata and C. virgata required 748-786 degree-days (Cd) and 1200 Cd respectively to progress from emergence to mature seed production. Freshly produced seeds of C. virgata were dormant for about 2 months, whereas 16-40% of seeds of C. truncata germinated within a week after maturation. Seed dormancy of C. virgata was released by the pre-treatment with 564 mM NaClO for 30 minutes. Exposure to light significantly increased germination of C. truncata seed from 0-2% in the dark to 77-84% in the light, and of C. virgata seed from 2-35% in the dark to 72- 85% in the light. Seeds of these two species could germinate over a wide temperature range (10-40oC), with maximum germination at 20-25oC for C. truncata and 15-25oC for C. virgata. The predicted base temperature for germination was 9.2-11.2oC for C. truncata and much lower 2.1-3.0oC for C. virgata. Seedling emergence of C. virgata (76% for seeds present on soil surface) was significantly reduced by burial at 1 (57%), 2 (49%) and 5 cm (9%), whereas seedling emergence of C. truncata was completely inhibited by burial of seed even at a shallow depth (0.5 cm). Under field conditions, both C. truncata and C. virgata seeds persisted in the soil for at least 11 months and seasons with below-average spring-summer rainfall increased seed persistence. Detailed studies were undertaken to identify glyphosate-resistant populations and to understand the mechanism of glyphosate resistance in C. truncata and C. virgata. Glyphosate resistance (GR) was confirmed in five populations of C. truncata and four populations of C. virgata. GR plants were 2.4 to 8.7-fold (C. truncata) and 2 to 9.7-fold (C. virgata) more resistant and accumulated less shikimate after glyphosate treatment than susceptible (S) plants. The differences in shikimate accumulation indicated that glyphosate did reach the target site but inhibited the EPSPS enzyme of each population differently. Glyphosate absorption and translocation did not differ between GR and S plants of either C. truncata or C. virgata. Two target-site EPSPS mutations (Pro-106-Leu and Pro-106-Ser) were likely to be the primary mechanism of glyphosate resistance in C. virgata but no previously known target-site mutations were identified in C. truncata. The C. virgata population with Pro-106-Leu substitution was 2.9 to 4.9-fold more resistant than those with Pro-106-Ser substitution. The primary mechanism of resistance to glyphosate in C. truncata was a combination of target-site EPSPS mutation (Glu-91-Ala) and amplification of the EPSPS gene. There were 16 to 48-fold more copies of the EPSPS gene in GR plants compared to S plants, with the number of EPSPS copies found to be variable both between and within populations.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food & Wine, 201

Lorentz TEM characterisation of magnetic and physical structure of nanostructure magnetic thin films

The work presented in this thesis is an investigation which aims to quantitatively characterise the physical microstructure, magnetic structure and micromagnetic behaviour of nanostructured thin films for magnetic recording and spintronics application. The nanostructures in the present work involve continuous and patterned thin films. Chapters 1, 2, and 3 present the overview backgrounds directly relevant to the work. Chapter 4 focuses on vortex structure in magnetic nanodots. The results confirm that the behaviour of the vortex can be modified by changing the edge geometry of the dots. It is demonstrated a practical method to determine the out-of-plane component of the vortex core with high accuracy and speed. Additionally in-plane curling magnetisation of the vortex is also mapped by reconstructing the electron phase using the transport-of-intensity equation. However this method is susceptible to spurious low spatial frequency and this aspect is explored to show limitations of the method. Chapter 5 deals with the characterisation of magnetic structure in nanoconstrictions intended to trap domain walls (DWs) in the nanoconstrictions. A structure was fabricated with two micron-sized pads as the sources for creation of DWs. A DW can be driven to be pinned at the nanoconstriction resulting in a change of magnetoresistance due to the contribution of the DW to the resistance of the device. The magnetisation configuration around the constriction is studied during the reversal process. It is apparent that that understanding the magnetisation rotation around the constriction and into the pads is the key to the magnetoresistance measurements and the DW resistance is part of this process. Evidences of DW compression at the nanoconstriction were noted. In Chapter 6 the investigation of the physical structure and micromagnetism of CoIr film is described. A hexagonal crystal structure with a [0001] texture normal to the film plane was characterised. Weak anisotropy is observed in the film denoted by a complex reversal on the hard axis due to incoherent rotation of magnetic moments. The film exhibits typical soft magnetic behaviour it merits compared to other soft materials are discussed in light of the results obtained here. Chapter 7 concludes with a discussion of the outcomes of the present thesis. Additionally possible directions for future research in topics discussed in this thesis are proposed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Modulation of domain wall dynamics in TbFeCo single layer nanowire

We demonstrate the possibility to write and modulate the magnetic domain walls in a TbFeCo single layer nanowire (300 nm width, 150 $\mu$m length). To realize this, a tiny magnetic domain was nucleated by an Oersted field produced by a 1.6 MHz pulse current (35 mA in amplitude, 5-40 ns in length) crossed the wire. To write the wall to the wire, a DC current was used to drive the nucleated domain (with two walls in two sides) to the wire in accordance with spin-transfer torque mechanism. A critical current density of $J_c = 3.5\times10^{10} Am^{-2}$ was required to control the motion of the walls in the wire. It was found that the size of the domain moving in the wire could be adjusted by either external field or the length of the nucleated pulse current. This could be considered as an important note for writing process in domain wall spin-torque devices, especially, memory elements.Comment: 14 pages, 5 figure

Broadcast Gossip Based Distributed Hypothesis Testing in Wireless Sensor Networks

We consider the scenario that N sensors collaborate to observe a single event. The sensors are distributed and can only exchange messages through a network to reach a consensus about the observed event. In this paper, we propose a very robust and simple method using broadcast gossip algorithm to solve the distributed hypothesis testing problem. The simulation result shows that our method has good performance and is very energy efficient comparing to existing methods

A TEM study of morphological and structural degradation phenomena in LiFePO₄-CB cathodes:Morphological and structural degradation in LiFePO4-CB cathodes

LiFePO4-based cathodes suffer from various degradation mechanisms which influences the battery performance. In this paper morphological and structural degradation phenomena in laboratory cathodes made of LiFePO4 (LFP) mixed with carbon black (CB) in an 1 mol L-1 LiPF6 in EC:DMC (1:1 by weight) electrolyte are investigated by transmission electron microscopy (TEM) at various preparation, assembling, storage and cycling stages. High-resolution TEM (HRTEM) imaging shows that continuous SEI layers are formed on the LFP particles and that both storage and cycling affects the formation. Additionally loss of CB crystallinity, CB aggregation and agglomeration is observed. Charge-discharge curves and impedance spectra measured during cycling confirm that these degradation mechanisms reduce the cathode conductivity and capacity.Comment: 5 figures, 2 table, journal article in International Journal of Energy Research, 201