Tailoring the magnetic anisotropy and domain patterns of sputtered TbFeGa alloys

We report the magnetic anisotropy and domain configuration of cosputtered TbFeGa alloys. The layers were deposited from two targets with compositions TbFe2 and Fe3Ga, respectively. The structural and magnetic properties do not only depend on the composition but also on the growth conditions. Alloys with the same composition but deposited using a DC or a pulsed power source in the TbFe2 target exhibit a different magnetic anisotropy. The perpendicular magnetic anisotropy, the size and topology of domain patterns can be tailored by changing the evaporation parameters of TbFe2. The width of the stripe domain increases from 235 to 835 nm when using the DC source in the TbFe2. We correlate this effect with Tb enrichment of the TbxFe1−x phases present in the samples

A mathematical model for domain walls in ultrathin magnetic films with uniaxial anisotropy

Domain walls are a basic ingredient of spintronic devices, nowadays. In this paper, a mathematical model for the solution of domain wall problems will be derived from a micromagnetic semiclassical approach. This model will prove to be suitable for the description of both Néel and Bloch walls, particularly in the case of magnetization uniformity distribution along the wall length of a uniaxial magnetic ultrathin film

Neurocomputer e dispositivi elettronici basati sullo spin

Current computers spend huge computational resources to process cognitive and perception-related functions, which humans routinely perform every day. This has recently resulted in a great change in the field of computation where research efforts have been addressed to the development of a neurocomputer that attempts to mimic the human brain starting from the underlying physical processes characterizing the nanoelectronic components and thereby using its efficiency in recognition problems. This paper attempts to provide a review of the recent developments in the field of spintronic device based neuromorphic computing

A first-principle model of the magnetic contrast in ultrathin films with perpendicular magnetization

In ultrathin films, the energy competition between the perpendicular magnetic anisotropy and the in-plane magnetostatic coupling can originate stripe domains. In such systems, the perpendicular magnetization component has a periodic modulation, pointing alternately upwards and downwards as the stripes are crossed. A measurement technique that is widely used to study these kind of domains is the magnetic force microscopy (MFM). As known, the MFM signal cannot be related immediately to the sample magnetization and the interpretation of the results is not always straightforward. Therefore, the achievement of a reliable contrast model for this technique in simple specific cases that could be directly compared with experimental results is highly desirable. In this paper, a first-principle model of the MFM contrast in the case of 1D magnetic nanostructures is proposed. An immediate application of the model pertains to the study of ultrathin films with perpendicular magnetization

X-ray-diffraction Study of P-doped Polycrystalline Si Thin-films Used In Ulsi Devices

A systematic study concerning texture of P-doped polycrystalline Si thin films has been performed. The as-deposited films display a (220) texture that has been shown to decrease with both annealing and P-doping whereas the (111) and (311) textures increase. Some samples have undergone oxidation. The effects on the texture of the oxidation process have been found to be not distinguishable from those of annealing. A quantitative approach has been followed in order to take into account the film thickness effect on the intensities of the X-ray diffraction peaks, often neglected in qualitative analyses. Such an approach showed that the generally ignored (311) texture is very important, especially for the low doped samples

X-ray diffraction study of P-doped polycrystalline Si thin films used in ULSI devices

A systematic study concerning texture of P-doped polycrystalline Si thin films has been performed. The as-deposited films display a (220) texture that has been shown to decrease with both annealing and P-doping whereas the (111) and (311) textures increase. Some sample have undergone oxidation. The effects on the texture of the oxidation process have been found to be not distinguishable from those of annealing. A quantitative approach has been followed in order to take into account the film thickness effect on the intensities of the x-ray diffraction peaks, often neglected in qualitative analyses. Such an approach showed that the generally ignored (311) texture is very important, especially for the low doped samples

STRIPES ROTATION AND MAGNETIC ANISOTROPY OF TbFeGa ALLOYS

Magnetic films with perpendicular magnetic anisotropy (PMA) are attractive materials for applications in the fields of high density magnetic recording and spintronics. The magnetic domains orientation is known to affect the signal propagation through these materials when used in spintronic devices. Recently, the PMA of TbFeGa alloys has been demonstrated [1]. In this work TbFeGa films were deposited by cosputtering, using two targets of TbFe2 and Fe3Ga. The effect of the type of power source (DC or pulsed) used in each target on the magnetic domain configuration has been investigated. It was found that the evaporation conditions strongly influence the out of plane (OOP) anisotropy of the films. Magnetic force microscopy (MFM), which shows the presence of stripe domains (fig. 1), has been used to investigate the rotatable anisotropy of these alloys. A magnetic field of variable intensity placed at 90 degrees with respect to the stripes direction has been applied, while in-field MFM images were recorded. The results clearly show the correlation between OOP and rotatable anisotropies, which allows to control the stripe domains rotation process and therefore the stripes orientation, by changing the films preparation conditions

Infrared light emission due to radiation damage in crystalline silicon

We have observed a set of broad luminescence bands between 1.07 and 0.85 eV, in He-implanted Si annealed in vacuum. These emissions are very similar to those of H-implanted and annealed Si, demonstrated by different groups in last years, in which H was believed to play a fundamental role. A comparison between the photoluminescence of He-implanted Si and of H-implanted Si, has allowed to conclude that the infrared photoluminescence of the Si:H system does not depend on H presence, but must be completely ascribed to the damage produced by the bombardment of Si with light ions. (C) 1997 Published by Elsevier Science Ltd. All rights reserved

On the role of the soft layer in exchange-spring hard/soft magnetic bilayers

Bilayers of SmCo/NiFe and SmCo/Co with well-defined in-plane uniaxial anisotropy were grown by dc magnetron sputtering on glass substrates. The magnetization reversal process was investigated by magneto-optic Kerr effect from both sides of the samples, obtaining the hard and soft response separately. The NiFe layers turn out to be exchange coupled to the SmCo films and, for soft layer thicknesses above 30 nm, display reversible demagnetization loops expected from exchange-spring magnets. The experimental NiFe magnetization curve is in good agreement with the theoretical curve obtained by minimizing the magnetic energy in the soft film for an ideal hard/soft bilayer. The soft layer critical thickness above which the exchange spring behavior sets up and its presumed independence on soft layer characteristics are discussed, by comparing the two systems under investigation. We find that SmCo/Co does not fulfil the predictions of the currently accepted theories and that the magnetization reversal of the bilayer is dominated by the Co layer

Vortex state suppression in an hexagonal array of interacting Py triangular rings

The magnetization reorientation process (MRP) of magnetic nanostructures displays novel features thanks to confinements effects due to nanostructures reduced dimensionality. As the applied field varies, the nanostructures magnetic configuration changes via domain walls (DWs) nucleation or annihilation; if magnetic materials with negligible magnetocrystalline anisotropy are used, this process is usually ruled just by the nanostructures shape. To make the MRP more reproducible and less sensitive to shape defects and to possible high energy magnetic configurations, e.g. vortex cores, the ring geometry is preferred. In this case, the magnetization process develops through magnetic configurations that are quite independent of the specific ring geometry [1,2], the so called onion state (OS) and the vortex state (VS). When inter-ring distance is small (less than one half of ring size) the dipolar interaction influence on the MRP becomes significant. In particular, during the MRP of triangular rings the DWs move and are trapped by ring corners so that the stray magnetic field may be intense. The influence of inter-ring interactions changes due to the rings shape, relative position and magnetic configuration [2]. The fields that produce the switch between OS and VS may accordingly change and a ring magnetic configuration may get less stable or even suppressed. In this contribution, we present the results obtained on an hexagonal array (HA) of Py equilateral triangular rings. The rings thickness is 25 nm, their side is 1.8 μm and their width is 230 nm. We adopt the hexagonal pattern and a reduced corner to corner distance (50 nm) in order to maximize the effect of inter-ring magnetic interactions. The magnetic reversal process was monitored for different directions of the in-plane applied field (H) through MFM measurements and longitudinal and diffraction magneto-optical Kerr effect, LMOKE and DMOKE, respectively. LMOKE gives access to the H dependence of the in-plane magnetization components; DMOKE to the H dependence of the magnetic form factor, also related to the symmetry of the nanostructure magnetic configuration [2]. Due to the presence of strong dipolar interactions, the rings of the HA display a long range magnetic order and, for a given H, they all display the same configuration. The MRP proceeds through the development of a VS in between two specularly symmetric OS; the VS is featured by a well-defined step in the LMOKE loops and by a peak in the DMOKE loops. For H parallel to the rings side (H//), the H range where the VS is stable is narrower than that observed in the isolated rings case [2]. For H perpendicular to the rings side (H_perp), the VS disappears whereas in the isolated case the VS was clearly observed. If the angle between H and a ring side, θ, is varied from 0, i.e. H//, to 30, i.e. H_perp, the width of the VS range of stability smoothly decreases and then goes abruptly to 0 for θ ~ 30. If θ is slightly varied around 30, the VS is not observed, as well. The observed difference between the H// and H_perp geometries may be due to the interplay between shape anisotropy energy and dipolar interaction energy; in H// shape anisotropy stabilizes the VS whilst in H_perp, as this direction is a symmetry axis of the triangular ring, shape anisotropy is less effective and the dipolar term prevails, stabilizing the OS configurations and canceling the VS. Indeed, the OS is the configuration where dipolar interaction are stronger, as 2 out of the 3 ring corners display a DW. The data will be discussed together with the results of micromagnetic calculations performed with the OOMMF software. The HA was simulated using groups of N rings (N = 3, 7) having different relative positions, to access different flux-closure configurations. The results will be discussed in terms of the stability of the vortex state. This work was supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement n°228673 (MAGNONICS). [1] M.F. Lai et al., J. Magn. Magn. Mater., 322 (2010) 92 [2] P. Vavassori, D. Bisero et al., Phys. Rev. B 78 (2008) 174403