In this letter, we report on electrical spin injection and detection in n-type germanium-on-insulator using a Co/Py/Al2O3 spin injector and 3-terminal non-local measurements. We observe an enhanced spin accumulation signal of the order of 1 meV consistent with the sequential tunneling process via interface states in the vicinity of the Al2O3/Ge interface. This spin signal is further observable up to 220 K. Moreover, the presence of a strong inverted Hanle effect points out the influence of random fields arising from interface roughness on the injected spins.

Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. In this letter, we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of n-Ge. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from 200 K up to room temperature. In this regime, the spin signal is reduced down to a value compatible with spin diffusion model. More interestingly, we demonstrate in this regime a significant modulation of the spin signal by spin pumping generated by ferromagnetic resonance and also by applying a back-gate voltage which are clear manifestations of spin current and accumulation in the germanium conduction band.

We have studied the thermal behavior of amphiphilic, symmetric triblock copolymers having short, deuterated polystyrene (PS) end blocks and a large poly(N-isopropylacrylamide) (PNIPAM) middle block exhibiting a lower critical solution temperature (LCST) in aqueous solution. A wide range of concentrations (0.1−300 mg/mL) is investigated using a number of analytical methods such as fluorescence correlation spectroscopy (FCS), turbidimetry, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and neutron spin-echo spectroscopy (NSE). The critical micelle concentration is determined using FCS to be 1 μM or less. The collapse of the micelles at the LCST is investigated using turbidimetry and DLS and shows a weak dependence on the degree of polymerization of the PNIPAM block. SANS with contrast matching allows us to reveal the core−shell structure of the micelles as well as their correlation as a function of temperature. The segmental dynamics of the PNIPAM shell are studied as a function of temperature and are found to be faster in the collapsed state than in the swollen state. The mode detected has a linear dispersion in q 2 and is found to be faster in the collapsed state as compared to the swollen state. We attribute this result to the averaging over mobile and immobilized segments.

We have measured the inverse spin Hall effect (ISHE) in n-Ge at room temperature. The spin current in germanium was generated by spin pumping from a CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch issue. A clear electromotive force was measured in Ge at the ferromagnetic resonance of CoFeB. The same study was then carried out on several test samples, in particular we have investigated the influence of the MgO tunnel barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO bilayer grown on SiO 2 exhibits a clear electromotive force due to anisotropic magnetoresistance and anomalous Hall effect which is dominated by an asymmetric contribution with respect to the resonance field. We also found that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample annealing systematically lead to an increase of the signal. We propose a theoretical model based on the presence of localized states at the interface between the MgO tunnel barrier and Ge to account for these observations. Finally, all of our results are fully consistent with the observation of ISHE in heavily doped n-Ge and we could estimate the spin Hall angle at room temperature to be ≈0.001.

In this letter, we first show electrical spin injection in the germanium conduction band at room temperature and modulate the spin signal by applying a gate voltage to the channel. The corresponding signal modulation agrees well with the predictions of spin diffusion models. Then by setting a temperature gradient between germanium and the ferromagnet, we create a thermal spin accumulation in germanium without any tunnel charge current. We show that temperature gradients yield larger spin accumulations than pure electrical spin injection but, due to competing microscopic effects, the thermal spin accumulation in germanium remains surprisingly almost unchanged under the application of a gate voltage to the channel.Comment: 7 pages, 3 figure

We have studied the thermal behavior of an ABA triblock copolymer having short, deuterated polystyrene end‐blocks and a longer poly(N‐isopropyl acrylamide) middle block, the latter exhibiting a lower critical solution temperature. The collapse of the micelles was investigated using dynamic light scattering. Small‐angle neutron scattering with contrast matching allowed us to quantify the core‐shell structure of the micelles as well as their correlations as a function of temperature.

Thin films of Ge1−xMnx containing Mn-rich nanostructures, so called nanocolumns, are grown by molecular-beam-epitaxy at low growth temperature (Tg) on Ge(001) substrate. Depending on the growth temperature, these nanocolumns can be either crystalline or amorphous. A quantitative study of magnetic anisotropy of these nanocolumns is performed by superconducting quantum interference device and electron paramagnetic resonance. We present a correlation between the structural morphology (diamond lattice) and the magnetic properties in these nanocolumns. Crystalline (Ge,Mn) nanocolumns (Tg=100 °C) exhibit fourth-order magnetic anisotropy due to the coupling between their magnetization and the cubic lattice whereas amorphous columns (Tg=150 °C) only exhibit second-order shape anisotropy.

We have grown Ge3Mn5 clusters by codepositing germanium and manganese atoms on Ge(001) substrates using low temperature molecular beam epitaxy and further annealing the films at high temperature. Clusters are spherical and randomly distributed in the germanium film in epitaxial relationship with the diamond lattice. They exhibit a broad size distribution. By performing a careful x-ray diffraction analysis, we could find that 97% of Ge3Mn5 clusters have their c-axis perpendicular to the film plane while 3% exhibit in-plane c-axis. We could also show a slight in-plane distortion of the Ge3Mn5 lattice leading to a reduction of uniaxial magnetic anisotropy. These observations are well confirmed by complementary superconducting quantum interference device and electron paramagnetic resonance measurements.