We demonstrate by magneto-transport measurements that a Curie temperature as high as 200 K can be obtained in nanostructures of (Ga,Mn)As. Heavily Mn-doped (Ga,Mn)As films were patterned into nanowires and then subject to low-temperature annealing. Resistance and Hall effect measurements demonstrated a consistent increase of T(C) with decreasing wire width down to about 300 nm. This observation is attributed primarily to the increase of the free surface in the narrower wires, which allows the Mn interstitials to diffuse out at the sidewalls, thus enhancing the efficiency of annealing. These results may provide useful information on optimal structures for (Ga,Mn)As-based nanospintronic devices operational at relatively high temperatures.

Naphthalene dipeptides have been shown to be useful low-molecular-weight gelators. Here we have used a library to explore the relationship between the dipeptide sequence and the hydrogelation efficiency. A number of the naphthalene dipeptides are crystallizable from water, enabling us to investigate the comparison between the gel/fiber phase and the crystal phase. We succeeded in crystallizing one example directly from the gel phase. Using X-ray crystallography, molecular modeling, and X-ray fiber diffraction, we show that the molecular packing of this crystal structure differs from the structure of the gel/fiber phase. Although the crystal structures may provide important insights into stabilizing interactions, our analysis indicates a rearrangement of structural packing within the fibers. These observations are consistent with the fibrillar interactions and interatomic separations promoting 1D assembly whereas in the crystals the peptides are aligned along multiple axes, allowing 3D growth. This observation has an impact on the use of crystal structures to determine supramolecular synthons for gelators.

Spin pumping is the phenomenon that magnetization precession in a ferromagnetic layer under ferromagnetic resonance produces a pure spin current in an adjacent non-magnetic layer. The pure spin current is converted to a charge current by the spin-orbit interaction, and produces a d.c. voltage in the non-magnetic layer, which is called the inverse spin Hall effect. The combination of spin pumping and inverse spin Hall effect has been utilized to determine the spin Hall angle of the non-magnetic layer in various ferromagnetic/non-magnetic systems. Magnetization dynamics of ferromagnetic resonance also produces d.c. voltage in the ferromagnetic layer through galvanomagnetic effects. Here we show a method to separate voltages of different origins using (Ga,Mn)As/p-GaAs as a model system, where sizable galvanomagnetic effects are present. Neglecting the galvanomagnetic effects can lead to an overestimate of the spin Hall angle by factor of 8, indicating that separating the d.c. voltages of different origins is critical.

We report the low-temperature magnetotransport behaviors of (Ga,Mn)As films with the nominal Mn concentration x larger than 10%. The ferromagnetic transition temperature TC can be enhanced to 191 K after postgrowth annealing (Ga,Mn)As with x=20%. The temperature Tm, corresponding to the resistivity minimum in the curve of resistivity versus temperature at temperature below TC, depends on Mn concentration, annealing condition, and magnetic field. Moreover, we find that the variable-range hopping may be the main conductive mechanism when temperature is lower than Tm.

In the past decades, the damping constant α has been successfully described theoretically-in some cases even quantitatively-using various approaches such as the breathing Fermi-surface model 1,2 , the torque correlation model 3 , scattering theory 4,5 and the torquetorque correlation within a linear response model 6,7 . On the basis of these works, α is expected to scale as α ~ n(E F )ξ 2 τ −1 under certain circumstances, where n(E F ) is the density of states at the Fermi level E F , ξ is the strength of the spin-orbit interaction and τ is the electron momentum scattering time 8,9 . Indeed, the dependences on n(E F ) (refs 9-11 ), ξ (refs 12,13 ) and τ (ref.14 ) have been confirmed separately in a large variety of materials. In general, it is assumed that damping is isotropic. However, several theoretical works [15][16][17][18] have suggested that damping should be anisotropic in single-crystalline ferromagnetic metals, such as bulk Fe, Co and Ni. This prediction is based on the anisotropic electronic structure where the shape of the Fermi surface depends on the orientation of the magnetization direction due to the spin-orbit interaction. The anisotropic electronic structure and thus the anisotropic damping, however, can be dramatically reduced due to smearing of the energy bands in the presence of electron scattering, which makes the experimental observation of the anisotropic damping in bulk materials difficult. So far, only a few experiments [19][20][21][22] have tried to prove the existence of anisotropic damping in bulk magnets but convincing experimental evidence is still lacking.Here, we report the observation of anisotropic Gilbert damping in a quasi-two-dimensional Fe/GaAs(001) system. The idea behind this is to explore the interfacial spin-orbit interaction of a singlecrystalline ferromagnetic metal/semiconductor interface. Our findings differ distinctly from the theoretical predictions made for bulk magnets. The Fe/GaAs heterostructure was intensively studied in the past two decades for semiconductor spintronics, and has been utilized, for example, to realize spin injection at room temperature 23 . Recently, interest in this system has been revived in view of spin-orbit electronics, because of the existence of robust spin-orbit fields at the Fe/GaAs interface, which can cause a mutual conversion between spin and charge currents at room temperature 24 . The spinorbit fields, including both Bychkov-Rashba-and Dresselhaus-like terms, result from the C 2v symmetry of the interface 25 . Specifically, at the Fe/GaAs(001) interface, Fe Bloch states near E F penetrate into GaAs. Therefore, electrons of Fe 'feel' both Bychkov-Rashba and Dresselhaus spin-orbit interaction at the interface, causing a rich variety of interfacial spin-orbit-related phenomena. It has been found, for example, that the symmetry of anisotropic magnetoresistance 26 and the polar magneto-optic Kerr effect 27 of Fe is governed by the twofold interfacial C 2v symmetry rather than its bulk fourfold C 4v symmetry when the thickne...

Elaborate morphology: The αSβ1 peptide, a fragment of α‐synuclein, assembles into flat tapes consisting of a peptide bilayer, which can be modeled based on the cross‐β structure found in amyloid proteins. The tapes are stabilized by hydrogen bonding, whilst the amphiphilic nature of the peptide results in the thin bilayer structure. To further stabilize the structure, these tapes may twist to form helical tapes, which subsequently close into nanotubes. Permissions: WILEY-VCH

Interfacial spin-orbit torques (SOTs) enable the manipulation of the magnetization through in-plane charge currents, which has drawn increasing attention for spintronic applications. The search for material systems providing efficient SOTs, has been focused on polycrystalline ferromagnetic metal/non-magnetic metal bilayers. In these systems, currents flowing in the non-magnetic layer generate—due to strong spin–orbit interaction—spin currents via the spin Hall effect and induce a torque at the interface to the ferromagnet. Here we report the observation of robust SOT occuring at a single crystalline Fe/GaAs (001) interface at room temperature. We find that the magnitude of the interfacial SOT, caused by the reduced symmetry at the interface, is comparably strong as in ferromagnetic metal/non-magnetic metal systems. The large spin-orbit fields at the interface also enable spin-to-charge current conversion at the interface, known as spin-galvanic effect. The results suggest that single crystalline Fe/GaAs interfaces may enable efficient electrical magnetization manipulation.

A compound two-dimensional ͑2D͒ monolayer mixing Mn atoms and 7,7,8,8-tetracyanoquinodimethane ͑TCNQ͒ molecules was synthesized by supramolecular assembly on a Cu͑100͒ surface under ultrahigh vacuum conditions. Its structural, electronic, and magnetic properties were analyzed by scanning tunneling microscopy experiment and theory, low-energy electron diffraction, x-ray photoemission spectroscopy, and densityfunctional theory calculations. The 2D compound has a long-range ordered square planar network structure consisting of fourfold coordinated Mn centers with a Mn:TCNQ ratio of 1:2. The electronic-state analysis revealed a complex charge-transfer scenario indicating strong bonding of TCNQ with both the Mn adsorbates and the Cu surface atoms. The calculations reveal that the Mn centers carry a magnetic moment close to 5 B with very weak coupling between adjacent Mn centers.