Magnetic properties of FeGa/Kapton for flexible electronics

Flexible materials have brought up a new era of application-based research in stretchable electronics and wearable devices in the last decade. Tuning of magnetic properties by changing the curvature of devices has significant impact in the new generation of sensor-based technologies. In this work, magnetostrictive FeGa thin films have been deposited on a flexible Kapton sheet to exploit the magneto-elastic coupling effect and modify the magnetic properties of the sample. The FeGa alloy has high magnetostriction constant and high tensile strength making its properties susceptible to external stress. Tensile or compressive strain generated by the convex or concave states influence the uniaxial magnetic anisotropy of the system. Low temperature measurements show a hard magnetic behavior and the presence of exchange-bias effect after field cooling to 2 K. The results obtained in this study prove essential for the development of flexible electronics

Tunable frequency ferromagnetic resonance of Co nanowire arrays

In order to overcome the current limitations of metallic systems for microwave applications, columnar arrays of Co nanowires with variable wire lengths were electrochemically grown using anodic alumina membranes with thickness of ~100 μm and pore diameters around 70 nm. The Co nanowires tend to present a strong hcp-magnetocrystalline anisotropy directed in the plane perpendicular to the wires axis. The combination of shape anisotropy directed along the wire axis (depending on the wire length) and the hcp magneto-crystalline anisotropy (due to structure) causes a shift from in-plane to out-of-plane spontaneous magnetization with relevant saturation and remanence magnetization values. Different types of magnetic behavior may then lead to ferromagnetic resonance frequencies shifting from 20 to 40 GHz at zero applied field

Study of the Temperature Dependence of Coercivity in MnBi

Two set of polycrystalline MnBi bulk samples, as-annealed and compacted powders, with different grain size, were prepared through powder metallurgy. Coercivity mechanisms were investigated by Kronmüller plot analysis, evaluating α and Neff parameters, which take into account the effect of microstructure. The temperature dependence of coercivity of the as-annealed sample (α= 0.31) is compatible with pinning-type mechanisms, while that of the compacted powders (α= 0.41) indicates nucleation-type processes. Irreversible effects of temperature dependence of coercivity have been investigated

Microstructure and magnetic properties of pure iron for cyclotron electromagnets

The microstructural and magnetic properties of pure iron ingots used as cores of cyclotron electromagnets have been investigated upon annealing sequence from 650 degrees C to 820 degrees C. Optical Microscopy, Scanning Electron Microscopy, and X-ray Diffraction were employed in the structural analysis, while magnetization curve and hysteresis loops were obtained in rod and ring samples, machined out of the large (around 4 m diameter) cast yoke, by combination of point-by-point and continuous (frequency f = 0.03 Hz) hysteresisgraph methods. Quite inhomogeneous grain structure was observed, with large and irregularly shaped grains (size of several mm), posing special constraints to the conventional magnetic testing approach (e.g., the IEC 60404-4 standard). Reproducible DC magnetic measurements could be performed using large cross-sectional area samples and suitable spatial averaging of the measured effective magnetic field, the eddy current effects being minimized at the same time. Full magnetic softening was obtained upon the annealing sequence in the absence of grain growth and change of distribution and morphology of the inclusions. The measured increase of permeability and decrease of coercivity are therefore entirely ascribed to the relief of the residual stresses, affecting the as-prepared and preliminarily annealed massive (similar to 80 x 10(3) kg) yoke. By recognizing in this way the role of stresses, we are eventually able to estimate the additional contributions to the material coercivity provided by the grain boundaries and the precipitated impurities, the latter playing a major role

Stripe domains and spin reorientation transition in Fe78B13Si9 thin films produced by rf sputtering

Magnetic thin films have been obtained by rf sputtering from an amorphous Fe(78)B(13)Si(9) target. The samples have been produced with thickness t ranging in the interval 25-1000 nm. Microstructural investigations indicate that the films have different microstructures varying from fully amorphous to partially nanocrystalline with increasing t. Magnetic hysteresis loops have been measured by means of high-sensitive magnetometry. A tailorable spin reorientation transition (SRT) from in-plane single-domain-like to out-of-plane multidomain state with increasing film thickness was observed. Magnetic force microscopy images have been obtained for all samples indicating that for t <= 80 nm the magnetization lies in the film plane. For larger thickness, a stripe domain pattern has been observed, indicating the presence of a magnetic anisotropy axis perpendicular to the film plane. In this work, SRT and stripe domain structure have been studied as a function of thickness and sample microstructure. (c) 2008 American Institute of Physics

Magnetization properties of FeTb thin films

The magnetic properties of FeTb rf-sputtered thin films have been investigated. While the as-prepared films are mainly amorphous, a successive annealing process caused the development of successive crystal phases. We observed the emergence of a variety of different domain structures, as the system crystal fraction evolves. The hysteretic behavior is shown to change as the internal stresses are released by annealing