Magnetostatic interactions in arrays of nanostructures

The physics of nanomagnetic elements has become one of the main areas of research in the last few decades. Their magnetic characterization is fundamental in order to understand the magnetic reversal mechanisms and to control the magnetic switching precisely in view of device applications. In such small elements, the magnetic behaviour is strongly determined by the interplay of magnetic anisotropy with the geometric shape. Moreover, in closed packed arrays, the effects of the inter-element interactions become important and reveal often unresolved issues regarding the strength of these couplings and their dipolar or exchange mediated origin. In this thesis three different cases have been discussed about the mechanisms of interactions among the magnetic elements of very densely packed systems. The experimental section opens with the study of the magnetization reversal process in magnetostatically interacting permalloy (an alloy of nickel and iron) nanowires, using the vectorial magneto-optical Kerr effect magnetometry. The measured in-plane magnetization components parallel and perpendicular to the applied field show a transition from coherent rotation to inhomogeneous reversal mode over and above a determined value of the wires thickness. A strong dependence on wires thickness is also observed in the analysis of effects of dipolar interactions. Successively, the motion and pinning of domain walls have been investigated in vertical and horizontal chains of permalloy triangular microrings and compared with the isolated rings case. Using longitudinal and diffracted magnetooptic Kerr effects, magnetic force microscopy and micromagnetic simulations, the field dependence of the spin structure into the ring has been determined. This investigation has allowed to observe how the dipolar inter-element interaction changes qualitatively the manner in which reversal occurs. Considering that the magnetic domain walls displacement can also be controlled by using magnetic fields, such structures could be viewed as a preliminary approach for the development of magnetic logic applications. Finally, static and dynamical properties have been studied in patterned arrays of pseudo spin-valves in which a layer of permalloy has been coupled with a layer of cobalt, through an interspacer of non-magnetic copper. Magnetic hysteresis loops have been measured by longitudinal magneto-optic Kerr effect and by X-ray resonant magnetic scattering, whereas the dynamical properties have been investigated using the Brillouin light scattering. The results show a complex magnetization reversal process determined by the interplay between the interlayer dipolar interaction and the different reversal nucleation fields in the two ferromagnetic layers. Reducing the thickness of the copper spacer, an interlayer magnetic exchange coupling between the permalloy and cobalt layers emerges, in addition to the dipolar interaction, introducing further possibilities for manipulating the magnetic behaviour of the system

Effectiveness of psycho-educational intervention to promote mental health focused on emotional intelligence in middle-school

Purpose. The specific “outcome-oriented” pattern of the emotional intelligence (EI) should be considered of capital importance for teenagers in order to promote mental health. Nevertheless it is rarely evaluated because a specific tool, useful for routinely use, is not available. In this paper the authors describe the effectiveness of a new approach of public health to improve the EI “outcome-oriented”, by a specific index.Design. A comparison of two samples: experimental (i.e. applying the program) vs control group, without randomization.Setting. 12 classes belonging to 3 different schools.Subjects. A sample of 276 students, 146 (53%) belonging to the experimental classes. Intervention. A program of 20 meetings, once a week, based on the handbook Intervento psicoeducativo per la promozione del benessere psicologico e dell’intelligenza emotiva nelle scuole (Psycho-educational intervention for promoting psychological well-being and emotional intelligence at school) in order to stimulate a “peer to peer student approach”.Measures. Index of emotional intelligence (15 items), inventory idea questionnaire (19 items), learning ability questionnaire (6 items).Analysis. Nonparametric tests were used.Results. The authors found significant statistical differences at the conclusion of the study for all considered measures.Conclusion. The results show a remarkable and positive impact of the approach above all on the “outcome-oriented” EI. Significant results were also observed about the indicator concerning irrational beliefs. The same significant results were found about learning abilities (goal definition, problem-solving and communication skills). The main limit is the study design (lack of randomization). Further evaluation is needed

Continuously graded anisotropy in single (Fe53Pt47)100−xCux films

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.We report on continuously graded anisotropy. During deposition, a compositional gradient is achieved by varying the Cu concentration from Cu-rich (Fe53Pt47)70Cu30 to Cu-free Fe53Pt47. The anisotropy gradient is then realized after annealing using the composition dependence of the low-anisotropy (A1) to high-anisotropy (L10) ordering temperature. The critical role of the annealing temperature on the resultant anisotropy gradient is investigated. Magnetic measurements support the creation of an anisotropy gradient in properly annealed films which exhibit both a reduced coercivity and moderate thermal stability. These results demonstrate that an anisotropy gradient can be realized, and tailored, in single continuous films without the need for multilayers

First-order reversal curve analysis of graded anisotropy FePtCu films

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The reversal mechanisms of graded anisotropy FePtCu films have been investigated by alternating gradient magnetometer AGM and magneto-optical Kerr effect MOKE measurements with first-order reversal curve FORC techniques. The AGM-FORC analysis, which clearly shows the presence of soft and hard components, is unable to resolve how these phases are distributed throughout the film thickness. MOKE-FORC measurements, which preferentially probe the surface of the film, reveal that the soft components are indeed located toward the top surface. Combining AGM-FORC with the inherent surface sensitivity of MOKE-FORC analysis allows for a comprehensive analysis of heterogeneous systems such as graded materials

Magneto-optical probe for investigation of multiphase fe oxide nanosystems

In iron oxide nanoparticles the transformation of the metastable magnetite phase to maghemite, through the oxidation of iron, often represents a major drawback for correct interpretation of their physical properties and their effective use in several applicative areas. To solve this issue we propose an innovative method for identifying the chemical composition of complex ferrite nanostructures based on magneto-optical (MO) spectroscopy. Spherical iron oxide nanoparticles with increasing size are investigated by magnetic circular dichroism (MCD) in the nUV-vis-nIR range (350-1000 nm). Particular attention is dedicated to the time evolution of the MO response, which is ascribable to the oxidation process of the nanomaterial. The measured MCD spectra show a complex line shape due to the overlap of several MO transitions. Deconvolution analysis of MCD hysteresis loops allows the interpretation of this complex response as the combination of two distinct contributions, originating from magnetite and maghemite domains in the nanoparticles. We consider this method a viable complement to conventional techniques for the discrimination of the two magnetic phases in nanostructured materials

Probing vertically graded anisotropy in FePtCu films

Field-dependent polarized neutron reflectivity (PNR) and magnetometry are employed to study the magnetic properties of compositionally uniform and graded FePtCu films as a function of annealing temperature (TA). The PNR results are able to directly probe the compositional and anisotropy variations through the film thickness. Further details about how the reversal mechanisms evolve are then elucidated by using a first-order reversal curve technique. The reversal of the graded sample annealed at 300º C occurs by an initial rapid switching of the dominant soft A1 phase toward the surface of the film, followed by the gradual reversal of the residual hard phase components toward the bottom. This indicates that the anisotropy gradient is not well established at this low TA. A fundamentally different mechanism is found after annealing at 400ºC, where the rapid switching of the entire film is preceded by a gradual reversal of the soft layers. This suggests that the anisotropy gradient has become better established through the film thickness. The field-dependent PNR measurements confirm the existence of an anisotropy gradient, where the lower (higher) anisotropy portions are now toward the bottom (top) of the film because of the Cu compositional gradient. However, after annealing at 500º C,a single rapid reversal is found, indicating the formation of a uniform hard film. In this case, PNR demonstrates a more uniform magnetic depth profile that is consistent with a uniform reference sample, suggesting significant interdiffusion of the Cu is degrading the compositional and induced anisotropy gradient at this elevated TA

Contribution of MUTYH variants to male breast cancer risk: results from a multicenter study in Italy

Inherited mutations in BRCA1, and, mainly, BRCA2 genes are associated with increased risk of male breast cancer (MBC). Mutations in PALB2 and CHEK2 genes may also increase MBC risk. Overall, these genes are functionally linked to DNA repair pathways, highlighting the central role of genome maintenance in MBC genetic predisposition. MUTYH is a DNA repair gene whose biallelic germline variants cause MUTYH-associated polyposis (MAP) syndrome. Monoallelic MUTYH variants have been reported in families with both colorectal and breast cancer and there is some evidence on increased breast cancer risk in women with monoallelic variants. In this study, we aimed to investigate whether MUTYH germline variants may contribute to MBC susceptibility. To this aim, we screened the entire coding region of MUTYH in 503 BRCA1/2 mutation negative MBC cases by multigene panel analysis. Moreover, we genotyped selected variants, including p.Tyr179Cys, p.Gly396Asp, p.Arg245His, p.Gly264Trpfs*7, and p.Gln338His, in a total of 560 MBC cases and 1,540 male controls. Biallelic MUTYH pathogenic variants (p.Tyr179Cys/p.Arg241Trp) were identified in one MBC patient with phenotypic manifestation of adenomatous polyposis. Monoallelic pathogenic variants were identified in 14 (2.5%) MBC patients, in particular, p.Tyr179Cys was detected in seven cases, p.Gly396Asp in five cases, p.Arg245His and p.Gly264Trpfs*7 in one case each. The majority of MBC cases with MUTYH pathogenic variants had family history of cancer including breast, colorectal, and gastric cancers. In the case-control study, an association between the variant p.Tyr179Cys and increased MBC risk emerged by multivariate analysis [odds ratio (OR) = 4.54; 95% confidence interval (CI): 1.17-17.58; p = 0.028]. Overall, our study suggests that MUTYH pathogenic variants may have a role in MBC and, in particular, the p.Tyr179Cys variant may be a low/moderate penetrance risk allele for MBC. Moreover, our results suggest that MBC may be part of the tumor spectrum associated with MAP syndrome, with implication in the clinical management of patients and their relatives. Large-scale collaborative studies are needed to validate these findings