Atomic-level structural and chemical analysis of Cr-doped Bi2Se3 thin films

We present a study of the structure and chemical composition of the Cr-doped 3D topological insulator Bi2Se3. Single-crystalline thin films were grown by molecular beam epitaxy on Al2O3 (0001), and their structural and chemical properties determined on an atomic level by aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy. A regular quintuple layer stacking of the Bi2Se3 film is found, with the exception of the first several atomic layers in the initial growth. The spectroscopy data gives direct evidence that Cr is preferentially substituting for Bi in the Bi2Se3 host. We also show that Cr has a tendency to segregate at internal grain boundaries of the Bi2Se3 film

The Winchcombe meteorite, a unique and pristine witness from the outer solar system.

Direct links between carbonaceous chondrites and their parent bodies in the solar system are rare. The Winchcombe meteorite is the most accurately recorded carbonaceous chondrite fall. Its pre-atmospheric orbit and cosmic-ray exposure age confirm that it arrived on Earth shortly after ejection from a primitive asteroid. Recovered only hours after falling, the composition of the Winchcombe meteorite is largely unmodified by the terrestrial environment. It contains abundant hydrated silicates formed during fluid-rock reactions, and carbon- and nitrogen-bearing organic matter including soluble protein amino acids. The near-pristine hydrogen isotopic composition of the Winchcombe meteorite is comparable to the terrestrial hydrosphere, providing further evidence that volatile-rich carbonaceous asteroids played an important role in the origin of Earth's water

Novel Approach Identifies SNPs in SLC2A10 and KCNK9 with Evidence for Parent-of-Origin Effect on Body Mass Index

Marja-Liisa Lokki työryhmien Generation Scotland Consortium, LifeLines Cohort Study ja GIANT Consortium jäsenPeer reviewe

NONVOLATILE FULL ADDER BASED ON A SINGLE MULTIVALUED HALL JUNCTION

Multivalued logic devices are promising candidates for achieving high-density, low-power memory and logic functionalities. We present a ferromagnetic multilayer Hall junction device with four distinct resistance - and thus logic - states. The states can be encoded as a quaternary bit and decoded into two binary bits. We demonstrate a nonvolatile full adder that is based on a single Hall junction, the extraordinary Hall balance. The device can be easily integrated into complex logic circuits for logic-in-memory architectures

Growth of Bi2Se3 and Bi2Te3 on amorphous fused silica by MBE

Topological insulator (TI) thin films of Biinline imageSeinline image and Biinline imageTeinline image have been successfully grown on amorphous fused silica (vitreous SiOinline image) substrates by molecular beam epitaxy. We find that such growth is possible and investigations by X-ray diffraction reveal good crystalline quality with a high degree of order along the c-axis. Atomic force microscopy, electron backscatter diffraction and X-ray reflectivity are used to study the surface morphology and structural film parameters. Angle-resolved photoemission spectroscopy studies confirm the existence of a topological surface state. This work shows that TI films can be grown on amorphous substrates, while maintaining the topological surface state despite the lack of in-plane rotational order of the domains. The growth on fused silica presents a promising route to detailed thermoelectric measurements of TI films, free from unwanted thermal, electrical, and piezoelectric influences from the substrate

Spin pumping through a topological insulator probed by x-ray detected ferromagnetic resonance

In the field of spintronics, the generation of a pure spin current (without macroscopic charge flow) through spin pumping of a ferromagnetic (FM) layer opens up the perspective of a new generation of dissipation-less devices. Microwave driven ferromagnetic resonance (FMR) can generate a pure spin current that enters adjacent layers, allowing for both magnetization reversal (through spin-transfer torque) and to probe spin coherence in non-magnetic materials. However, standard FMR is unable to probe multilayer dynamics directly, since the measurement averages over the contributions from the whole system. The synchrotron radiation-based technique of x-ray detected FMR (XFMR) offers an elegant solution to this drawback, giving access to element-, site-, and layer-specific dynamical measurements in heterostructures. In this work, we show how XFMR has provided unique information to understand spin pumping and spin transfer torque effects through a topological insulator (TI) layer in a pseudo-spin valve heterostructure. We demonstrate that TIs function as efficient spin sinks, while also allowing a limited dynamic coupling between ferromagnetic layers. These results shed new light on the spin dynamics of this novel class of materials, and suggest future directions for the development of room temperature TI-based spintronics

Spin pumping in ferromagnet-topological insulator-ferromagnetheterostructures

Topological insulators (TIs) are enticing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. However, a means to interact with and exploit the topological surface state remains elusive. Here, we report a study of spin pumping at the TI-ferromagnet interface, investigating spin transfer dynamics in a spin-valve like structure using element specific time-resolved x-ray magnetic circular dichroism and ferromagnetic resonance. Gilbert damping increases approximately linearly with increasing TI thickness, indicating efficient behaviour as a spin sink. However, layer-resolved measurements suggest that a dynamic coupling is limited. These results shed new light on the spin dynamics of this novel material class and suggest great potential for TIs in spintronic devices, through their novel magnetodynamics that persist even up to room temperature

Extraordinary hall balance

Magnetoresistance (MR) effects are at the heart of modern information technology. However, future progress of giant and tunnelling MR based storage and logic devices is limited by the usable MR ratios of currently about 200% at room-temperature. Colossal MR structures, on the other hand, achieve their high MR ratios of up to 106% only at low temperatures and high magnetic fields. We introduce the extraordinary Hall balance (EHB) and demonstrate room-temperature MR ratios in excess of 31,000%. The new device concept exploits the extraordinary Hall effect in two separated ferromagnetic layers with perpendicular anisotropy in which the Hall voltages can be configured to be carefully balanced or tipped out of balance. Reprogrammable logic and memory is realised using a single EHB element. PACS numbers: 85.75.Nn,85.70.Kh,72.15.Gd,75.60.Ej

Magnetic proximity-enhanced Curie temperature of Cr-doped Bi₂Se₃ thin films

We report a study on the transition temperature, T_C, of a Cr-doped Bi2Se3 topological insulator thin film, where an increase in the ferromagnetic onset can provide a pathway towards low-power spintronics applications. Arrott plots, obtained by Cr L_2,3 x-ray magnetic circular dichroism as a function of field at various low temperatures, give a T_C ~7 K. This is similar to the bulk value of the sample, which means that there is no indication the spontaneous magnetization is different near the surface. Evaporation of a thin layer of Co onto the pristine surface of the in-situ cleaved sample increases the ordering temperature to ~19 K. X-ray absorption spectroscopy shows that Cr enters the Bi2Se3 host matrix in a divalent state, and is unchanged by the Co deposition