The influence of glass coating on the single domain wall potential in amorphous glass-coated Fe-based microwires

The effect of the glass coating on the single domain wall potential in amorphous glass-coated Fe-based microwire has been studied by the switching field distribution technique. The thermoactivated mechanism model is used to describe the thermally activated switching through the complex energy barrier in amorphous FeSiB microwires. Glass removal leads to the increase of the probability of the thermally activated switching pointing to the decrease of the energy barrier.     

Tunable effective permittivity of composites based on ferromagnetic microwires with high magneto-impedance effect

The effect of the external magnetic field on the dispersion of the effective permittivity in a single array of parallel CoFe-based amorphous wires is demonstrated by measuring the transmission/reflection spectra in free space in the frequency band of 0.9–17 GHz. The magnetic field is applied along the wires, sensitively changing their magnetisation and high-frequency impedance. Based on the measurements of magneto-impedance in a single wire and S-parameters of composites in free space, we show the correlation between the magneto-impedance and the field dependence of the effective permittivity.     

Manipulating the magnetoimpedance by dc bias current in amorphous microwire

We have studied the effect of the internal circumferential magnetic field H_B created by the dc bias current I_B on longitudinal and off-diagonal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that by changing the dc current I_B it is possible to considerably change the MI dependencies. The bias current applied to such microwire transforms the symmetric and hysteretic MI curve to asymmetrical and anhysteretic. The minimum of longitudinal MI curve shifts from the zero-field point. Reversing the bias current causes reversal of the bias field direction and results in a mirroring of the MI curves. It is proposed to apply a cross-checking of two MI curves with I_B of different polarity for magnetic field sensing. In particular, this method allows to overcome the drawbacks usually associated with longitudinal MI—namely the impossibility to determine the direction of an external axial magnetic field H_E and the low sensitivity near the zero-field point. Moreover, the operating range of the longitudinal MI sensor, in contrast to the off-diagonal one, can be much extended as it exhibits a quite high sensitivity in the field range up to one order of magnitude higher than the anisotropy field.     

Magnetoelastic contribution in domain wall dynamics of amorphous microwires

We studied the domain wall (DW) propagation of magnetically-bistable Fe–Co-rich microwires paying attention to the effect of applied and internal stresses. Magnetic field, H, dependences of DW velocity, v, were measured in Co_41.7Fe_36.4Si_10.1B_11.8 microwires with metallic nucleus diameters (from 13 μm to 18 μm) and with different ρ-ratio between the metallic nucleus diameter, d, and total microwire diameter, D. DW velocity decreased under the application of stresses. From measured dependences we evaluated DW mobility, S, dependence on the applied stresses. The results obtained for Co_41.7Fe_36.4Si_10.1B_11.8 sample show that S decreases with the increasing of applied stresses, σ_a. The observed dependences manifest that increasing of magnetoelastic anisotropy results in the decreasing of DW mobility and DW velocity     

Domain wall propagation in Fe-rich amorphous microwires

The domain wall (DW) propagation in magnetically bistable Fe₇₄Si₁₁B₁₃C₂ amorphous microwires with metallic nucleus diameters of 12–16 μm has been investigated in order to explain high DW velocities observed in Sixtus–Tonks like experiments. In micrometric wires, the boundary between two head-to-head domains is very elongated. The DW mobility normal to the wall surface is reduced by the domain aspect ratio and is in the range of a few m/s/Oe in the linear regime. The experimental results in the viscous regime could be quantitatively explained in terms of the domain length and normal mobility limited by the eddy currents and spin relaxation losses.     

Linear and non-linear response of embedded Na clusters

We investigate Na clusters embedded in Ar matrices. The surrounding Ar atoms are modeled in terms of their dynamical polarizability and the strong electron repulsion. The calibration of the model is discussed. First results for the non-linear optical response of the Na clusters are presented for the test case of Na₈ embedded in Ar ensembles of different sizes. It is shown that blue shift through core repulsion and red shift through dipole polarizability counterweight each other to the end that very little global shift is seen in the spectra. This feature persists to all excitation strengths considered. There are, however, detailed effects, such as for example the Landau fragmentation of the Mie plasmon peak. PACS 36.40.Gk; 36.40.Vz; 31.15.Ew     

Modularity of Some Distance Graphs

Doklady Mathematics - New bounds on the modularity of distance graphs were obtained and the exact value of modularity was calculated for G(n, 2, 1) graphs.