Spin current propagation through ultra-thin insulating layers in multilayered ferromagnetic systems

Spin current pumping from a ferromagnet through an insulating layer into a heavy metal was studied in a CoFeB/SiO2/Pt system in relation to the thickness and interfacial structure of the insulating layer. The propagation of spin current from the ferromagnet into the heavy metal falls rapidly with sub-nanometer thicknesses of SiO2 and is suppressed beyond a nominal thickness of 2 nm. Structural analysis shows that SiO2 only forms a complete barrier layer beyond around 2 nm, indicating that the presence of a discontinuous insulating barrier, and not tunneling or diffusion, explains the main observations of spin-pumping with thin insulating layers

Characterisation of Charge Conduction Networks in Poly(3-hexylthiophene)/Polystyrene Blends using Noise Spectroscopy

1/f noise spectroscopy is used to investigate charge conduction networks within polymer blend space-charge-limited diodes (SCLDs) fabricated from regioregular poly(3-hexylthiophene) (P3HT) and either isotactic-polystyrene (i-PS) or amorphous-polystyrene (a-PS). Conducting AFM measurements showed that i-PS blends have heterogeneous conduction characterised by current ‘hotspots’, whereas a-PS blends showed homogeneous conduction. The difference in conducting networks between blends was clearly revealed when examining the noise spectra for the range of blend devices. Furthermore, the shape of the noise spectra suggested that as the blend composition changed, the charges sampled differing breadths of the density of states. These data suggest that noise measurements can be used as an informative technique to electrically characterise the effects of blend morphology and its effects within polymer electronic devices

TITAN's Digital RFQ Ion Beam Cooler and Buncher, Operation and Performance

We present a description of the Radio Frequency Quadrupole (RFQ) ion trap built as part of the TITAN facility. It consists of a gas-filled, segmented, linear Paul trap and is the first stage of the TITAN setup with the purpose of cooling and bunching radioactive ion beams delivered from ISAC-TRIUMF. This is the first such device to be driven digitally, i.e., using a high voltage ($V_{pp} = \rm{400 \, V}$), wide bandwidth ($0.2 < f < 1.2 \, \rm{MHz}$) square-wave as compared to the typical sinusoidal wave form. Results from the commissioning of the device as well as systematic studies with stable and radioactive ions are presented including efficiency measurements with stable $^{133}$Cs and radioactive $^{124, 126}$Cs. A novel and unique mode of operation of this device is also demonstrated where the cooled ion bunches are extracted in reverse mode, i.e., in the same direction as previously injected.Comment: 34 pages, 17 figure

Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes

We study the spectra of neutron-rich oxygen isotopes based on chiral two- and three-nucleon interactions. First, we benchmark our many-body approach by comparing ground-state energies to coupled-cluster results for the same two-nucleon interaction, with overall good agreement. We then calculate bound excited states in 21,22,23O, focusing on the role of three-nucleon forces, in the standard sd shell and an extended sdf7/2p3/2 valence space. Chiral three-nucleon forces provide important one- and two-body contributions between valence neutrons. We find that both these contributions and an extended valence space are necessary to reproduce key signatures of novel shell evolution, such as the N = 14 magic number and the low-lying states in 21O and 23O, which are too compressed with two-nucleon interactions only. For the extended space calculations, this presents first work based on nuclear forces without adjustments. Future work is needed and open questions are discussed.Comment: 6 pages, 4 figures, published versio

UHECR as Decay Products of Heavy Relics? The Lifetime Problem

The essential features underlying the top-down scenarii for UHECR are discussed, namely, the stability (or lifetime) imposed to the heavy objects (particles) whatever they be: topological and non-topological solitons, X-particles, cosmic defects, microscopic black-holes, fundamental strings. We provide an unified formula for the quantum decay rate of all these objects as well as the particle decays in the standard model. The key point in the top-down scenarii is the necessity to adjust the lifetime of the heavy object to the age of the universe. This ad-hoc requirement needs a very high dimensional operator to govern its decay and/or an extremely small coupling constant. The natural lifetimes of such heavy objects are, however, microscopic times associated to the GUT energy scale (sim 10^{-28} sec. or shorter). It is at this energy scale (by the end of inflation) where they could have been abundantly formed in the early universe and it seems natural that they decayed shortly after being formed.Comment: 11 pages, LaTex, no figures, updated versio

Inelastic scattering of 9Li and excitation mechanism of its first excited state

The first measurement of inelastic scattering of 9Li from deuterons at the ISAC facility is reported. The measured angular distribution for the first excited state confirms the nature of excitation to be an E2 transition. The quadrupole deformation parameter is extracted from an analysis of the angular distribution.Web of Scienc

Investigation of the role of 10^{10}Li resonances in the halo structure of 11^{11}Li through the 11^{11}Li(p, d)10^{10}Li transfer reaction

International audienceThe first measurement of the one-neutron transfer reaction 11Li(p,d)10Li performed using the IRIS facility at TRIUMF with a 5.7AMeV11Li beam interacting with a solid H2 target is reported. The 10Li residue was populated strongly as a resonance peak with energy Er=0.62 ±0.04MeV having a total width $\Gamma$ = 0.33 ±0.07MeV. The angular distribution of this resonance is characterized by neutron occupying the 1p1/2orbital. A DWBA analysis yields a spectroscopic factor of 0.67 ±0.12for p1/2 removal strength from the ground state of 11Li to the region of the peak

Spin transport across the interface in ferromagnetic/nonmagnetic systems

Understanding interfacial spin transport is key to developing magnetoelectonic devices, however, the exact nature of the parameters involved is unclear. Here, we report a detailed ferromagnetic resonance-based spintransport analysis on a variety of structures of both ferromagnetic (Co, CoFeB) and heavy metal layers (Pt, Ru) in order to fully quantify the interfacial spin-transport parameters. Enhanced spin-mixing conductance is observed for more closely matched ferromagnet and heavy metal crystal structures, and, significantly, the inclusion of a thickness-dependent spin-diffusion length gives a bulk value of 9.4 ± 0.7 nm for Pt, resolving reported discrepancies

Verifying the accuracy of the TITAN Penning-trap mass spectrometer

TITAN (TRIUMF's Ion Traps for Atomic and Nuclear science) is an online facility designed to carry out high-precision mass measurements on singly and highly charged radioactive ions. The TITAN Penning trap has been built and optimized in order to perform such measurements with an accuracy in the sub ppb-range. A detailed characterization of the TITAN Penning trap is presented and a new compensation method is derived and demonstrated, verifying the performance in the range of sub-ppb