Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mossbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magneto-resistance devices can be further tailored using ultrathin magnetic layers.Comment: 9 pages, 3 figure

Growth mechanisms and process window for InAs V-shaped nanoscale membranes on Si[001]

Organized growth of high aspect-ratio nanostructures such as membranes is interesting for opto-electronic and energy harvesting applications. Recently, we reported a new form of InAs nano-membranes grown on Si substrates with enhanced light scattering properties. In this paper we study how to tune the morphology of the membranes by changing the growth conditions. We examine the role of the V/III ratio, substrate temperature, mask opening size and inter-hole distances in determining the size and shape of the structures. Our results show that the nano-membranes form by a combination of the growth mechanisms of nanowires and the Stranski-Krastanov type of quantum dots: in analogy with nanowires, the length of the membranes strongly depends on the growth temperature and the V/III ratio; the inter-hole distance of the sample determines two different growth regimes: competitive growth for small distances and an independent regime for larger distances. Conversely, and similarly to quantum dots, the width of the nano-membranes increases with the growth temperature and does not exhibit dependence on the V/III ratio. These results constitute an important step towards achieving rational design of high aspect-ratio nanostructures

III-V nanowire arrays: growth and light interaction

Semiconductor nanowire arrays are reproducible and rational platforms for the realization of high performing designs of light emitting diodes and photovoltaic devices. In this paper we present an overview of the growth challenges of III-V nanowire arrays obtained by molecular beam epitaxy and the design of III-V nanowire arrays on silicon for solar cells. While InAs tends to grow in a relatively straightforward manner on patterned (111) Si substrates, GaAs nanowires remain more challenging; success depends on the cleaning steps, annealing procedure, pattern design and mask thickness. Nanowire arrays might also be used for next generation solar cells. We discuss the photonic effects derived from the vertical configuration of nanowires standing on a substrate and how these are beneficial for photovoltaics. Finally, due to the special interaction of light with standing nanowires we also show that the Raman scattering properties of standing nanowires are modified. This result is important for fundamental studies on the structural and functional properties of nanowires

Bottom-up engineering of InAs at the nanoscale: From V-shaped nanomembranes to nanowires

The ability to rationally tune the morphology of nanostructures is a fundamental milestone in nanoscale engineering. In particular, the possibility to switch between different shapes within the same material system represents a further step in the development of complex nanoscale devices and it increases the potential of nanostructures in practical applications. We recently reported a new form of InAs nanostructures growing epitaxially on Si substrates as vertical V-shaped membranes. Here we demonstrate the possibility of modifying the shape of these nanomembranes and turning them into nanowires by modulating the surface roughness of the substrate by varying the surface treatment. We show that the growth of nanomembranes is favored on smooth surfaces. Conversely rough surfaces enhance the growth of nanowires. We also shove that the V/III ratio plays a key role in determining the absolute yield, i.e. how many nanostructures form during growth. These results envisage a new degree of freedom in the engineering of bottom up nanostructures and contribute to the achievement of nanostructure networks. (C) 2015 Elsevier B.V. All rights reserved

Gonadal function in male patients after treatment for malignant lymphomas, with emphasis on chemotherapy

Gonadal function was assessed in male lymphoma survivors based on serum hormone levels (LH, FSH, testosterone, SHBG), and was related to treatment, age and observation time. Male patients ⩽50 years at diagnosis treated for Hodgkin's (HL) and/or non-Hodgkin's lymphoma (NHL) at the Norwegian Radium Hospital from 1 January 1980 to 31 December 2002 were included. Five treatment groups were defined: 1: radiotherapy only and/or low gonadotoxic chemotherapy (both HL and NHL)(‘No/low'), 2: medium gonadotoxicity chemotherapy for NHL (‘med-NHL'), 3: medium gonadotoxicity chemotherapy for HL (‘med-HL'), 4: highly gonadotoxic chemotherapy for NHL (‘high-NHL'), 5: highly gonadotoxic chemotherapy for HL (‘high-HL'). Gonadal hormone levels were categorised into three groups: 1: All gonadal hormones within normal range (normal), 2: Isolated elevated FSH, with LH, SHBG and testosterone within normal range (exocrine hypogonadism), 3: Testosterone below and/or LH above normal range (endocrine hypogonadism). One hundred and forty-four (49%) of the patients had normal gonadal hormones, 60 (20%) displayed exocrine hypogonadism and almost one-third (n=90, 30%) had endocrine hypogonadism. Compared to those treated with no/low gonadotoxic chemotherapy patients from all other treatment groups had significantly elevated risk for exocrine hypogonadism. Patients from the other treatment groups, except those in the med-NHL group, also had significantly elevated risk for endocrine hypogonadism compared with the group treated with no/low gonadotoxic chemotherapy. Men aged above 50 years at survey were about five times more likely to have endocrine hypogonadism compared with those less than 40 years. Because of the adverse health effects following long-lasting endocrine hypogonadism, gonadal hormones should be assessed regularly in male lymphoma survivors, especially after treatment with alkylating agents and high-dose chemotherapy with autologous stem cell support and in male patients who are 50 years and older

Current developments in SWIPPA ‘Space Weather Impact on Precise Positioning Applications of GNSS’

SWIPPA (Space Weather Impact on Precise Positioning Applications of GNSS) is a project, initiated by DLR, aiming at establishing a specific space weather (SW) service for improving current Global Navigation Satellite System (GNSS) applications. This activity is considered as being a substantial part of the preparations for the future European Space Weather Programme and GALILEO services. The SWIPPA project started with the definition of service, including user requirements, products, and related technical service definition. Following on the multiple discussions within the project consortium, all requirements of each user service have been carefully considered. It was important to obtain information on issues such as: which products are most needed and which should have higher priority than others, the optimal spatial and time resolution, products improvements, etc. The established information security and classification policy within the project is of primary importance and is strictly observed to protect the rights and interests of the SWIPPA customer. As a result of the user requirements, the final SWIPPA products list has been created. The products list include various nowcast and forecast maps, expert estimates, warning geophysical messages, etc. A sub-set of the listed products can become available to the SWENET (Space Weather European Network) and general public members following their interest and further discussions. Based on the user requirements and the products definition, the most adequate technical solutions have been sought and found considering the powerful technological base and rich experience available at DLR. All information will be operationally processed at the DLR premises, the products will be developed and placed on FTP server(s) providing near realtime access to the most recently generated data products. The ‘definition of service’ part has been successfully completed. The SWIPPA project continued recently with the establishment of service, including the built up of infrastructure and central processing facilities. Preliminary navigation data and products have been already transferred between DLR and its partners/users for testing purposes. In resume, the project is progressing well in time. The efforts are first in this field and require each space-weather service to be carefully adjusted to the specific needs of the SWIPPA users

Magnetization reversal in individual Py and CoFeB nanotubes locally probed via anisotropic magnetoresistance and anomalous Nernst effect

Using anisotropic magnetoresistance in a multi-probe configuration and local heating with a scanning laser, we investigate the magnetization reversal of individual permalloy (Py) and CoFeB nanotubes with spatial resolution. Nanocrystalline Py and amorphous CoFeB nanotubes are found to reverse via domain wall movement and chirality switching, respectively. Our experiments provide an understanding of the role of microstructure and magnetic anisotropy in the switching of ferromagnetic nanotubes at room temperature

On the relation between network RTK performance and ionospheric activity

GNSS RTK (Real-Time Kinematic) positioning techniques are based on precise but ambiguous carrier phase observations. The ambiguities can be resolved by properly modelling the ionospheric influence. However, under perturbed ionospheric conditions, the ionospheric modelling may become inaccurate and thus to lead to degraded network performance. The paper addresses the adverse space weather effects on GNSS-based positioning and discusses possible problems of reference network concepts that can be attributed to ionospheric interference in particular. For the purpose, analysed is the relation between the residual ionospheric error and the ionospheric activity. Generally, the ionospheric impact is noticeably stronger during ionospheric perturbations/storms, which raises the question of how the reference networks perform during such unfavourable conditions. Analysed also is the feasibility and effectivity of an operational space weather monitoring service for improving the performance and maintaining the integrity of network RTK