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The correlation between magnetic anisotropy and magnetoimpedance has been studied in field- and stress-annealed Fe73.5Cu1Nb3Si13.5B9 ribbons. As-cast and previously nanocrystallized samples were submitted to different annealing conditions (T=500, 530, and 560 °C and tensile stress σ=150 MPa) in order to induce different magnetic anisotropy. The magnetoimpedance ratio [ΔZ/Z] was measured at 3 MHz using a driving current Irms=10 mA. An hysteretic behavior of the magnetoimpedance ratio is observed. This hysteretic behavior is interpreted considering the magnetization process for samples exhibiting different magnetic anisotropies.

Articles you may be interested inTunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films Appl. Phys. Lett. 105, 102409 (2014); 10.1063/1.4895708 Magnetoimpedance and magnetization processes of FeCoNi electroplated tubesVery large magnetoimpedance effect in FeCoNi ferromagnetic tubes with high order magnetic anisotropy Magnetoimpedance effect in CoFeNi plated wire with ac field annealing destabilized domain structure A giant magnetoimpedance effect ͑GMI͒ has been measured in a CuBe 0.1 mm diameter wire, electroplated with a Co 6 Fe 20 Ni 74 layer 1 m thick. Heat treatments after the electrodeposition were performed under the dc or ac field. The GMI has been measured in the frequency range 0.25 to 9 MHz, using ac driving current from 5 to 35 mA. The maximum GMI ratio depends strongly on the heat treatments, the intensity and the frequency of the driving current, reaching the value of 165% for optimal conditions. Results are discussed, taking into account the anisotropy distribution in the magnetic layer induced by the heat treatments under the field and a simple rotation model.

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Articles you may be interested inVery large magnetoimpedance effect in FeCoNi ferromagnetic tubes with high order magnetic anisotropy

Present day biomedical applications, including magnetic biosensing, demand better understanding of the interactions between living systems and magnetic nanoparticles (MNPs). In this work spherical MNPs of maghemite were obtained by a highly productive laser target evaporation technique. XRD analysis confirmed the inverse spinel structure of the MNPs (space group Fd-3m). The ensemble obeyed a lognormal size distribution with the median value 26.8 nm and dispersion 0.362. Stabilized water-based suspensions were fabricated using electrostatic or steric stabilization by the natural polymer chitosan. The encapsulation of the MNPs by chitosan makes them resistant to the unfavorable factors for colloidal stability typically present in physiological conditions such as pH and high ionic force. Controlled amounts of suspensions were used for in vitro experiments with human blood mononuclear leukocytes (HBMLs) in order to study their morphofunctional response. For sake of comparison the results obtained in the present study were analyzed together with our previous results of the study of similar suspensions with human mesenchymal stem cells. Suspensions with and without chitosan enhanced the secretion of cytokines by a 24-h culture of HBMLs compared to a control without MNPs. At a dose of 2.3, the MTD of chitosan promotes the stimulating effect of MNPs on cells. In the dose range of MNPs 10–1000 MTD, chitosan “inhibits” cellular secretory activity compared to MNPs without chitosan. Both suspensions did not caused cell death by necrosis, hence, the secretion of cytokines is due to the enhancement of the functional activity of HBMLs. Increased accumulation of MNP with chitosan in the cell fraction at 100 MTD for 24 h exposure, may be due to fixation of chitosan on the outer membrane of HBMLs. The discussed results can be used for an addressed design of cell delivery/removal incorporating multiple activities because of cell capability to avoid phagocytosis by immune cells. They are also promising for the field of biosensor development for the detection of magnetic labels.