Coupling efficiency for phase locking of a spin transfer oscillator to a microwave current

The phase locking behavior of spin transfer nano-oscillators (STNOs) to an external microwave signal is experimentally studied as a function of the STNO intrinsic parameters. We extract the coupling strength from our data using the derived phase dynamics of a forced STNO. The predicted trends on the coupling strength for phase locking as a function of intrinsic features of the oscillators i.e. power, linewidth, agility in current, are central to optimize the emitted power in arrays of mutually coupled STNOs

Effect of Crystallographic Texture on Magnetic Characteristics of Cobalt Nanowires

Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition in etched ion-track polycarbonate membranes. Structural characterization of these nanowires with diameter 70, 90, 120 nm and length 30 μm was performed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction techniques. The as-prepared wires show uniform diameter along the whole length and X-ray diffraction analysis reveals that [002] texture of these wires become more pronounced as diameter is reduced. Magnetic characterization of the nanowires shows a clear difference of squareness and coercivity between parallel and perpendicular orientations of the wires with respect to the applied field direction. In case of parallel applied field, the coercivity has been found to be decreasing with increasing diameter of the wires while in perpendicular case; the coercivity observes lower values for larger diameter. The results are explained by taking into account the magnetocrystalline and shape anisotropies with respect to the applied field and domain transformation mechanism when single domain limit is surpassed

Uniaxial Magnetization Performance of Textured Fe Nanowire Arrays Electrodeposited by a Pulsed Potential Deposition Technique

Textured ferromagnetic Fe nanowire arrays were electrodeposited using a rectangular-pulsed potential deposition technique into anodized aluminum oxide nanochannels. During the electrodeposition of Fe nanowire arrays at a cathodic potential of ??1.2 V, the growth rate of the nanowires was ca. 200 nm s?1. The aspect ratio of Fe nanowires with a diameter of 30?±?5 nm reached ca. 2000. The long axis of Fe nanowires corresponded with the direction when a large overpotential during the on-time pulse was applied, whereas it orientated to the direction under the potentiostatic condition with a small overpotential. By shifting the on-time cathode potential up to ??1.8 V, the texture coefficient for the (200) plane, TC200, reached up to 1.94. Perpendicular magnetization performance was observed in Fe nanowire arrays. With increasing TC200, the squareness of Fe nanowire arrays increased up to 0.95 with the coercivity maintained at 1.4 kOe at room temperature. This research result has opened a novel possibility of Fe nanowire arrays that can be applied for a new permanent magnetic material without rare-earth metals

Dipolar interactions in multilayered Co0.96Cu0.04/Cu nanowire arrays

Arrays of electrodeposited Co0.96Cu0.04/Cu nanowires into porous polycarbonate membranes have been characterized by ferromagnetic resonance measurements in order to study the effect of the dipolar interactions on the effective anisotropy field as a function of the magnetic and non magnetic layer thickness. It is found that breaking the infinite cylinder geometry reduces their shape anisotropy field, which can be modified to a large extent from 6.5 kOe for non layered nanowires down to nearly zero for layered nanowires with the thinnest magnetic layers. An analytical model is proposed to describe the magnetostatic interactions between magnetic layers and their effect on the total anisotropy field which shows a good agreement with the experiment

Configurable multiband microwave absorption states prepared by field cycling in arrays of magnetic nanowires

Arrays of low diameter bi-stable electrodeposited magnetic nanowires demagnetized in the direction parallel to the wires are used to prepare non-saturated stable magnetic states formed by groups of wires magnetized positive and negative with respect to the applied field. Exploiting the coercive field distribution, both the number of wires in each group as well as the number of different groups can be varied by changing the demagnetizing cycle parameters. The ferromagnetic resonance field and peak intensity are shown to be different for each of these magnetic states. By applying demagnetizing cycles, it is possible to induce multiple absorption peaks, and thus show field-programmable multiband absorption properties

Ferromagnetic nanocylinders electrodeposited into nanoporous alumina template: A magnetometry and Brillouin light scattering study

The static magnetization experimental behavior of cobalt (Co), Permalloy (Py), and nickel (Ni) nanocylinders is obtained from vibrating sample magnetometry while the dynamic behavior for the Co and Py ones is analyzed by means of Brillouin light scattering spectroscopy. Assuming the presence at remanence of two populations of cylinders with up and down magnetizations and including the dipolar coupling between the cylinders, a single analytical model based on a mean-field approach allowed us to satisfactorily analyze both series of experimental results. The model requires three physical parameters, allowing us to derive the in-plane saturation field, the eigenfrequency in the absence of applied field, and the eigenfrequency at the in-plane saturation field; these parameters enable us to adjust the whole variation of the eigenfrequency versus the applied field. Moreover, the effect of the magnetocrystalline anisotropy on the softening of the frequency in the nonsaturated state is clearly evidenced: it is more pronounced when the magnetocrystalline anisotropy is not vanishing and adds to the shape anisotropy (Co c-axis parallel to the cylinder axis); the softening being weak in the other cases (Co c-axis perpendicular to the cylinder axis or Permalloy)

Application of the anisotropy field distribution method to arrays of magnetic nanowires

The applicability of the anisotropy field distribution method and the conditions required for an accurate determination of the effective anisotropy field in arrays of magnetic nanowires have been evaluated. In arrays of magnetic nanowires that behave as ideal uniaxial systems having only magnetostatic contributions to the effective anisotropy field, i.e., shape anisotropy and magnetostatic coupling, the method yields accurate values of the average anisotropy field at low-moderate dipolar coupling and accuracy decreases as wire packing increases. When an additional non-negligible magnetocrystalline anisotropy is present, the method is less accurate, as shown for the case of hcp Co nanowires