86,703 research outputs found
Specific loss power of magnetic nanoparticles: A machine learning approach
No full textA machine learning approach has been applied to the prediction of magnetic hysteresis properties (coercive field, magnetic remanence, and hysteresis loop area) of magnetic nanoparticles for hyperthermia applications. Trained on a dataset compiled from numerical simulations, a neural network and a random forest were used to predict power losses of nanoparticles as a function of their intrinsic properties (saturation, anisotropy, and size) and mutual magnetic interactions, as well as of application conditions (temperature, frequency, and applied field magnitude), for values of the parameters not represented in the database. The predictive ability of the studied machine learning approaches can provide a valuable tool toward the application of magnetic hyperthermia as a precision medicine therapy tailored to the patient's needs. (C) 2022 Author(s)
Magnetoresistance anisotropy in a hexagonal lattice of Co antidots obtained by thermal evaporation
No full textPatterned soft magnetic materials are eligible for use in magnetic random access memories. A hexagonal-lattice pattern of circular antidots was produced by optical lithography in a Co film. In order to test the effect of geometry on the local magnetisation configuration of such a structure, we performed room-temperature angle-resolved magnetisation measurements aimed to check the pinning of domain walls by the pattern's lattice. Magnetoresistance (MR) room-temperature measurements were performed at various angles between the magnetic field direction and the macroscopic electrical current vector, to clarify whether and how the local current density configuration affects the MR response. We found that the magnetoresistance is of anisotropic type (AMR) and has a local origin. Furthermore, the largely unsaturating behaviour of MR at high fields may be explained only by considering that tiny portions of the pattern constitute highly frustrated regions and align their magnetisation at rather high fields. A simplified model based on a local anisotropy term is shown to account for the experimental results for both M and M
Effect of thermal treatment on high-frequency magneto-impedance in ferromagnetic/Cu/ferromagnetic trilayers
No full textAnomalous low-temperature magnetoresistance dips in sputtered ferromagnetic thin films and multilayers
No full textA set of ferromagnetic thin films and multilayers containing 3d metals (Fe, Co) in different amounts was prepared by rf sputtering. Each sample exhibits a specific magnetic and magnetoresistive behavior, as expected for materials having different saturation magnetizations, magnetic anisotropies, and surface-to-volume ratios. From room temperature down to about 10 K, the magnetoresistance is explained in terms of well-known mechanisms; at low fields, a negative magnetoresistance is measured. Between similar to 10 and 30 K, the zero-field electrical resistance appears to be dominated by electron-phonon scattering. At lower temperatures, where the R vs T curve is almost saturated, a sudden drop of the resistance appears, whose magnitude and position vary from sample to sample. Below the drop temperature, a region of positive magnetoresistance is systematically observed at around H=0 in measurements done with the magnetic field applied either parallel or perpendicular to the film plane. The dip magnitude increases with decreasing temperature. The anomaly appears to be related to the presence of magnetic inhomogeneity in the samples. The experimental results are not explained in terms of standard magnetoresistance mechanisms. Effects related to quantum coherence of conduction electrons may be the source of the observed anomalies. The role of weak localization of electrons, inhibited by the additional scattering provided by the magnetic inhomogeneity on the nanometer scale, is discussed
Spin reorientation transition in amorphous FeBSi thin films submitted to thermal treatments
No full textDewetting Process in Ni-Mn-Ga Shape-Memory Heusler: Effects on Morphology, Stoichiometry and Magnetic Properties
No full textIn this work, dewetting process has been investigated in shape-memory Heuslers. To this aim, series of high-temperature annealing (1100–1150 K) have been performed at high vacuum (time is varied in the range of 55–165 min) in Ni-Mn-Ga epitaxial thin films grown on MgO(001). The process kinetics have been followed by studying the evolution of morphology and composition. In particular, we report the initiation of the dewetting process by the formation of symmetric holes in the films. The holes propagate and integrate, leaving micrometric and submicron islands of the material, increasing the average roughness of the films by a factor of up to around 30. The dewetting process is accompanied by severe Ga and Mn sublimation, and Ni-Ga segregation, which significantly modify the magnetic properties of the films measured at each stage. The annealed samples show a relatively weak magnetic signal at room temperature with respect to the pristine sample
Magnetic nanoparticle aggregation states in Ag100-xFex cosputtered granular films investigated by magnetic and magnetotransport measurements
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