Suppression of spin rectification effects in spin pumping experiments

Spin pumping (SP) is a well-established method to generate pure spin currents allowing efficient spin injection into metals and semiconductors avoiding the problem of impedance mismatch. However, to disentangle pure spin currents from parasitic effects due to spin rectification effects (SRE) is a difficult task that is seriously hampering further developments. Here we propose a simple method that allows suppressing SRE contribution to inverse spin Hall effect (ISHE) voltage signal avoiding long and tedious angle-dependent measurements. We show an experimental study in the well-known Py/Pt system by using a coplanar waveguide (CPW). Results obtained demonstrate that the sign and size of the measured transverse voltage signal depends on the width of the sample along the CPW active line. A progressive reduction of this width evidences that SRE contribution to the measured transverse voltage signal becomes negligibly small for sample width below 200 μm. A numerical solution of the Maxwell equations in the CPW-sample setup, by using the Landau-Lifshitz equation with the Gilbert damping term (LLG) as the constitutive equation of the media, and with the proper set of boundary conditions, confirms the obtained experimental results.

Magnetic molecules as sensors of topological hysteresis of superconductors

Superconductors and magnetic materials, including molecules, are key ingredients for quantum and advanced spintronic applications. However, only a little is known about how these materials are mutually influenced at their interface in hybrid architectures. Here, we show that a single layer of magnetic molecules, the Terbium(III) bis-phthalocyaninato (TbPc2) complexes, deposited on a superconducting Pb(111) surface is sensitive to the topology of the intermediate state of the superconductor, namely to the presence and evolution of superconducting and normal domains due to the magnetic field screening and penetration. The evidence of this sensitivity is found in the magnetisation dynamics of the TbPc2 sub-monolayer in its paramagnetic regime showing the fingerprint of the topological hysteresis of the superconducting substrate. This study reveals the great potentialities hold by thin layers of magnetic molecules for sensing local magnetic field variation in hybrid molecular/superconductor architectures, including spin resonators or spin injection devices for spintronics applications.

Enhanced spin accumulation in nano-pillar-based lateral spin valve using spin reservoir effect

Lateral spin valves are ideal nanostructures for investigating spin-transport physics phenomena and promoting the development of future spintronic devices owing to dissipation-less pure spin current. The magnitude of the spin accumulation signal is well understood as a barometer for characterizing spin current devices. Here, we develop a novel fabrication method for lateral spin valves based on ferromagnetic nanopillar structures using a multi-angle deposition technique. We demonstrate that the spin-accumulation signal is effectively enhanced by reducing the lateral dimension of the nonmagnetic spin channel. The obtained results can be quantitatively explained by the confinement of the spin reservoir by considering spin diffusion into the leads. The temperature dependence of the spin accumulation signal and the influence of the thermal spin injection under a high bias current are also discussed.

Development of a spin-injection device utilising Gadolinium Nitride

<p>In this thesis, the first steps in creating a realisable spin-injection transistor using ferromagnetic semiconductor electrodes are detailed. A spin-injection device utilising the ferromagnetic semiconductor gadolinium nitride has been designed, fabricated and electrically tested. In addition, an experimental setup for future measurements of a spin current in spin-injection devices was adapted to our laboratory-based off one developed by the Shiraishi group at Kyoto University. Issues encountered during fabrication were identified, and an optimal method for fabricating these devices was determined. Gadolinium nitride and copper were used to make the devices on Si/SiO2 substrates. The electrical integrity and applicability of the devices for future measurements of injected spin-current was determined through electrical device testing. Resistance measurements of electrical pathways within the device were undertaken to determine the successful deposition of the gadolinium nitride and copper. IV measurements to determine if the devices could withstand the current required for spin current measurements were done. The durability of the devices through multiple measurement types was observed. It was determined that although spin-injection devices utilising gadolinium nitride can be successfully fabricated, more work needs to be done to ensure that the electrical pathways through the copper and gadolinium nitride can be consistently reproducible to allow spin-injection measurements to be done.</p>

Development of a spin-injection device utilising Gadolinium Nitride

<p>In this thesis, the first steps in creating a realisable spin-injection transistor using ferromagnetic semiconductor electrodes are detailed. A spin-injection device utilising the ferromagnetic semiconductor gadolinium nitride has been designed, fabricated and electrically tested. In addition, an experimental setup for future measurements of a spin current in spin-injection devices was adapted to our laboratory-based off one developed by the Shiraishi group at Kyoto University. Issues encountered during fabrication were identified, and an optimal method for fabricating these devices was determined. Gadolinium nitride and copper were used to make the devices on Si/SiO2 substrates. The electrical integrity and applicability of the devices for future measurements of injected spin-current was determined through electrical device testing. Resistance measurements of electrical pathways within the device were undertaken to determine the successful deposition of the gadolinium nitride and copper. IV measurements to determine if the devices could withstand the current required for spin current measurements were done. The durability of the devices through multiple measurement types was observed. It was determined that although spin-injection devices utilising gadolinium nitride can be successfully fabricated, more work needs to be done to ensure that the electrical pathways through the copper and gadolinium nitride can be consistently reproducible to allow spin-injection measurements to be done.</p>

Effective modulation of spin accumulation using a ferromagnetic/nonmagnetic bilayer spin channel

A lateral spin valve consisting of highly spin-polarized CoFeAl electrodes with a CoFeAl/Cu bilayer spin channel has been developed. Despite a large spin absorption into the CoFeAl capping channel layer, an efficient spin injection and detection using the CoFeAl electrodes enable us to observe a clear spin valve signal. We demonstrate that the nonlocal spin accumulation signal is significantly modulated depending on the relative angle of the magnetizations between the spin injector and absorber. The observed modulation phenomena is explained by the longitudinal and transverse spin absorption effects into the CoFeAl channel layer with the spin resistance model.

Enhanced Spin Accumulation in Semiconductor at Room Temperature Using Ni0.65Zn0.35Fe2O4(NZFO) as Spin Injector in NZFO/MgO/p-Si Device

In this article, the fabrication of a Ni0.65Zn0.35Fe2O4/MgO/p-Si heterostructure device has been optimized using the pulsed laser deposition (PLD) technique, and a detailed investigation of its structural, electrical, and magnetic features has been performed experimentally. The electronic and magneto-transport characteristics have been explored in the temperature range of 100–300 K. The current-voltage (I-V) characteristics of the heterojunction have been recorded, which displayed an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The application of an external magnetic field parallel to the plane of the NZFO film causes the current (I) across the junction to decrease, clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. The root of displaying positive magnetoresistance in our heterojunction has been well justified using the standard spin injection model. The electrical injection of spin-polarized carriers and its accumulation and detection in a p-Si channel have been demonstrated using the NZFO/MgO tunnel contact using a three-terminal (3-T) Hanle device. The parameters such as spin lifetime (99 ps), spin diffusion length (276 nm), and spin polarization (0.44) have been estimated from the Hanle curve detected in our heterostructure at room temperature, making the Ni0.65Zn0.35Fe2O4/MgO/p-Si device a very favorable promising junction structure in the field of spintronics for several device appliances in the future.