The pairing symmetry of the superconducting material Strontium Ruthenate (Sr2RuO4), despite much research, has not been established. The experimental evidence until now points to a pairing symmetry...Show moreThe pairing symmetry of the superconducting material Strontium Ruthenate (Sr2RuO4), despite much research, has not been established. The experimental evidence until now points to a pairing symmetry compatible with the existence of superconducting domains. The boundaries of these domains are expected to act as Josephson junctions. Although bulk samples contain a random and non-predictable domain structure, mesoscopic samples feature a controllable configuration of the domains. The behavior of singly or doubly presupposed connected domain boundary is investigated by the electronic transport properties of mesoscopic samples of Sr2RuO4, in which the domain walls are pinned to the geometry. The characteristic critical current oscillations and Shapiro steps of the Josephson junction are established, as well as current switchable states due to in-plane (IP) fields.Show less
In an effort to control triplet superconductivity in ferromagnetic disks with RF signals a setup was built to support high frequency experiments in a vector magnet cryostat. This setup included the...Show moreIn an effort to control triplet superconductivity in ferromagnetic disks with RF signals a setup was built to support high frequency experiments in a vector magnet cryostat. This setup included the fabrication of on-substrate coplanar waveguides which can be used to couple RF signals to existing devices by fabricating the devices on top of the waveguide. Another component is the addition of a shielding box which can both block low frequency resonances and can make connecting to the on-substrate waveguides more convenient and reliable. To test the setup, ferromagnetic resonance experiments were done on permalloy thin films using a vector network analyser in addition to the vector magnet.Show less
This work presents a study of two types of spin-triplet Josephson junctions that are characterised by superconducting quantum interference and Shapiro step measurements. The first type of system is...Show moreThis work presents a study of two types of spin-triplet Josephson junctions that are characterised by superconducting quantum interference and Shapiro step measurements. The first type of system is a cobalt/niobium disk where long-range triplets are generated by the spin texture of a ferromagnetic vortex. The second system is a mesoscopic ring of Sr2RuO4, which is expected to host intrinsic Josephson junctions by the presence of chiral domain walls. For the cobalt/niobium disk, two supercurrent channels have been found surprisingly close to the edges of the disk by quantum interferometry measurements while indications of 0-pi segments have been found by the observation of half-integer Shapiro steps. Two rings with different inner and outer radii of Sr2RuO4 are shown to behave as Josephson junctions. The configurations of these junctions depend on the ring dimensions and the temperature. These findings make a convincing case for the presence of chiral domains in Sr2RuO4.Show less
In this study we investigate if we can change the interfacial conductivity in LaAlO3/SrTiO3 heterostructures by adding some oxygen to the argon sputter gas. We vary the deposition parameters to...Show moreIn this study we investigate if we can change the interfacial conductivity in LaAlO3/SrTiO3 heterostructures by adding some oxygen to the argon sputter gas. We vary the deposition parameters to minimise the effect of the oxygen. We find that an increase in oxygen partial pressure increases the surface roughness. We also find that an increase in argon flow increases surface roughness. The optimised parameters, which minimise surface roughness, are in agreement with previous results of growing a conducting interface in LaAlO3/SrTiO3 by sputtering. However all our samples grown with oxygen are found to be insulating. A possible explanation for the effect of oxygen in the sputter gas is that the species oxidise before reaching the sample. We conclude that even a very small amount of oxygen in the sputter gas gives an insulating interface and that we can not make a conducting interface with oxygen in the sputter gas with the experimental set-up used.Show less
In this thesis, we have worked on devices for two oxide systems, with which spin-polarized currents could in future be controlled. Firstly, we have worked on the optimization of growth parameters...Show moreIn this thesis, we have worked on devices for two oxide systems, with which spin-polarized currents could in future be controlled. Firstly, we have worked on the optimization of growth parameters for the depositions of La0.7Sr0.3MnO3 thin-films in off-axis sputtering. We have characterized the grown films using Atomic Force Microscopy, X-Ray Diffraction and resistance measurements. La0.7Sr0.3MnO3 is a ferromagnetic oxide, which we believe could be used in conjunction with the oxide superconductor Sr2RuO4 to induce polarized supercurrents. Further, we illustrate a lithography procedure which allows for the patterning of LSMO films into Hall bar structures. Next, we have designed a side-gated Hall bar pattern for LaAlO3/EuTiO3/SrTiO3 devices. This system has been shown to give rise to a spin-polarized two dimensional electron gas [1]. Our structure is designed to allow for local control of this spin-polarization.Show less
In this thesis we are interested in growing LaAlO3 films onto SrTiO3 substrates with an off-axis geometry radio frequency magnetron sputtering technique in order to study the properties of the...Show moreIn this thesis we are interested in growing LaAlO3 films onto SrTiO3 substrates with an off-axis geometry radio frequency magnetron sputtering technique in order to study the properties of the Q2DES found at the interface between this two band insulators. Hall bars with an Al2O3 hard mask were patterned onto TiO2-terminated SrTiO3 substrates. The selected lithographic process was electron beam lithography due to its high resolution. With respect to the growing of the Al2O3 hard mask two different approaches were used.Show less
Together with numerical computations, we have characterized the transport properties of devices with notched Permalloy nanowires. The driving mechanism of current-induced domain wall motion has...Show moreTogether with numerical computations, we have characterized the transport properties of devices with notched Permalloy nanowires. The driving mechanism of current-induced domain wall motion has been the subject of much debate. Permalloy is, with its easy axis along the nanowire, a good candidate to study the fundamental properties of a current-induced domain wall velocity, as its magnetic properties are well defined. A strong temperature dependence of the anisotropic magnetoresistance has been found, resulting in a decrease of the (de)pinning fields when the temperature increases. We believe that temperature is an important factor to take into account in studying the domain wall dynamics, and can even be helpful in identifying the relevant driving mechanism in current-induced domain wall motion. Although a start is made on the experimental realisation of domain wall velocity experiments in the PPMS (Physical Property Measurement System), much effort is still necessary in order to conduct actual velocity measurements.Show less
In this report, we discuss the possibility to use Josephson junctions as superconducting memory devices. These Josephson junctions are SFS (Superconductor-Ferromagnet-Superconductor) junctions. Due...Show moreIn this report, we discuss the possibility to use Josephson junctions as superconducting memory devices. These Josephson junctions are SFS (Superconductor-Ferromagnet-Superconductor) junctions. Due to a magnetization gradient, we generate triplet supercurrent at the interface. The junctions are disk-shaped, with cobalt on the bottom as the ferromagnet and niobium on top as the superconductor. Through the niobium, a trench is milled, to create the junction. The magnetization of the cobalt is circular in a pattern called a vortex. In the center the magnetization comes out of the plane. This is called the vortex core, and splits the junction into two channels. We can push this vortex core out with an in-plane field. By measuring out-of-plane interference patterns, we can calculate the spatial supercurrent distribution. By measuring such patterns with and without the vortex, we have shown that these SFS Josephson junctions can be used as superconducting memory devices.Show less
A method is proposed for patterning hall-bar structures within the LaAlO3/SrTiO3 interface. LaAlO3 was grown (10 u.c.) by means of off-axis magnetron sputtering, resulting in a conducting interface...Show moreA method is proposed for patterning hall-bar structures within the LaAlO3/SrTiO3 interface. LaAlO3 was grown (10 u.c.) by means of off-axis magnetron sputtering, resulting in a conducting interface exhibiting similar R(T) behavior to literature. This is one of the first reports on a conducting interface by means of sputtering, as LaAlO3 is conventionally grown by Pulse Laser Deposition. The beforementioned hall-bar structure, including a sufficient measurement set-up, allowed for ionic liquid gating experiments on the LaAlO3/SrTiO3 interface. The resistance was shown to increase for negative gate voltages (depletion mode), whereas positive gate voltages (enhancement mode) decreased the resistance. A clear distinction from the general R(T) behavior of the interface was shown to occur in depletion mode, as the resistance showed a huge upturn at low temperatures. Further investigation of hall-effect measurements has revealed the tunability of both the charge carrier density and the electron mobility by means of ionic liquid gating. The charge carrier density was shown to be roughly linearly dependent on the gate voltage at 170 K. The magnitude of the gate current, the reversibility of the gating effect, and the estimated capacitance of the system are clear ndications on the electrostatic nature of the gating effect within the LaAlO3/SrTiO3 interface, in the range of applied gate voltages. The previously described results allow for many interesting (ionic liquid gating) experiments on the LaAlO3/SrTiO3 interface in the near future.Show less
Sr2RuO4 is a leading candidate for equal-spin triplet pairing with p-wave chiral symmetry. This study presents a method for fabricating mesoscopic structures of Sr2RuO4. The samples are contacted...Show moreSr2RuO4 is a leading candidate for equal-spin triplet pairing with p-wave chiral symmetry. This study presents a method for fabricating mesoscopic structures of Sr2RuO4. The samples are contacted by conventional electron beam lithography methods. A measurement set-up using a vector magnet cryostat was prepared for transport measurements. We observe a high residual resistance ratio indicating high sample quality. The onset of signs of superconductivity appear at 1.5 K, as expected. Crystals with a thickness below 20 nm are found to be insulating, the origin is currently not understood.Show less
Domain wall manipulation in ferromagnets shows great promise for the development of fast and efficient computer memory devices. In particular, chromium dioxide has a half-metal characteristic that...Show moreDomain wall manipulation in ferromagnets shows great promise for the development of fast and efficient computer memory devices. In particular, chromium dioxide has a half-metal characteristic that holds the potential for reducing the heat produced from reading or writing memory bits. To reliably control the motion of domain walls, CrO2 nanowires are created with geometric anisotropy that acts as a potential well to ”pin” domain walls to fixed sites. Each wire was grown using selective-area growth to avoid the creation of random pinning sites from crystal disorder. This process is sensitive to many different factors in the creation of the SiO2 mask. Different effects can interfere with each other, including the proximity effect from electron beam lithography and a sensitivity to the levels of oxygen in the doped SiO2. This thesis presents methods of correction for individual effects, as well as initial results of domain wall mechanics in CrO2 nanowires. Using MFM measurements, I show the static pinning of a domain wall at the predicted pinning location. Magnetoresistance measurements of CrO2 wires ranging from 700 nm to 900 nm wide show that, at this scale, the dominant influence on the domain wall mechanics remains the magnetocrystalline anisotropy, instead of shape anisotropy as desired.Show less
Triplet superconductivity in lateral Josephson junctions has only been shown in the ferromagnet CrO2. We succeeded in creating a disk-shaped lateral cobalt Josephson junction with a trench width...Show moreTriplet superconductivity in lateral Josephson junctions has only been shown in the ferromagnet CrO2. We succeeded in creating a disk-shaped lateral cobalt Josephson junction with a trench width below 20 nm. The device shows promising signs of superconducting triplet correlations. For exchange fields up to 15 mT we see an increase in the critical current, possibly caused by an increase of the magnetic non-collinearity as the Ni generating layer aligns with the field. We also observe oscillations in the critical current. These oscillations have a period of approximately 4 mT and are believed to be the result of a flux quantisation effect in the superconducting cobalt disk.Show less
