R.L. Sommer

LONGITUDINAL AND TRANSVERSE MAGNETO-IMPEDANCE IN AMORPHOUS FE73.5CU1NB3SI13.5B9 FILMS

Magneto‐impedance effects have been observed in thin films of amorphous Fe73.5Cu1Nb3Si13.5B9. Large magneto‐impedance values have been obtained in field‐annealed samples, but not in as‐deposited samples. Transverse magneto‐impedance effects with magnitudes comparable to the longitudinal case have been observed. These results are discussed in terms of appropriate magnetic permeability.

Role of magnetic anisotropy in the magnetoimpedance effect in amorphous alloys

The magnetoimpedance (MI) effect of amorphous Co70.4Fe4.6Si15B10 ribbons, subjected to different annealing conditions with and without an external field, has been measured up to a frequency of 100 kHz. We show that the large MI effect is the result of transverse magnetic anisotropy, which is present in the as‐cast and the suitably field‐annealed samples.

Universality beyond power laws and the average avalanche shape

Stefanos Papanikolaou, Felipe Bohn, 3 Rubem Luis Sommer, Gianfranco Durin, 5 Stefano Zapperi, 5 and James P. Sethna LASSP, Department of Physics, Clark Hall, Cornell University, Ithaca, NY 14853-2501 Escola de Ciências e Tecnologia, Universidade Federal do Rio Grande do Norte, 59072-970, Natal, RN, Brazil Centro Brasileiro de Pesquisas F́ısicas, Rua Dr. Xavier Sigaud 150, Urca, Rio de Janeiro, RJ, Brazil INRIM, Strada delle Cacce 91, 10135 Torino, Italy ISI Foundation, Viale S. Severo 65, 10133 Torino, Italy CNR-IENI, Via R. Cozzi 53, 20125 Milano, Italy LASSP, Physics Department, Clark Hall, Cornell University, Ithaca, NY 14853-2501

Tailoring the magnetoimpedance effect of NiFe/Ag multilayer

The magnetoimpedance (MI) effect was investigated in NiFe/Ag multilayered (ML) and ML/SiO2/Ag/SiO2/ML structured multilayered (SD) ferromagnetic films grown by magnetron sputtering. The MI measurements were performed with an impedance analyzer over a wide frequency range, from 10 MHz to 1.8 GHz. Sample geometries are mainly responsible for the different MI behaviours and by considering the entire frequency range, distinct mechanisms responsible for MI changes were associated. For the ML sample, a maximum value of 80%, associated with the appearance of ferromagnetic resonance (FMR), was reached at around 1 GHz. For the SD sample, the striking feature is the existence of two distinct frequency ranges with high MI% values of 80% at around 100 MHz, related to the skin and magnetoinductive effects, and of 120% at around 1 GHz, associated with the strong skin and FMR effect.

Giant magneto‐impedance effects in Metglas 2705M

Giant magneto‐impedance (GMI) results for Metglas 2705M have been studied in two measuring geometries in several field annealed samples. A rich variety of peak features in GMI, all within a small field range, have been observed. The various features in the GMI are discussed in terms of magnetic susceptibility and microstructural properties of the amorphous ribbon.

Magnetization dynamics as derived from magneto impedance measurements

In this work, the magnetization dynamics of soft magnetic materials is studied with the aid of transverse differential permeability μ(Iac,f,Hdc) spectra. Contributions to the magnetization processes from domain wall motion and rotation of the magnetization can be extracted from the transverse differential permeability data which are in turn obtained from impedance Z(Iac,f,Hdc) spectra. In particular, an iteration method is used to extract μ(Iac,f,Hdc) from Z(Iac,f,Hdc) data. The approach is tested in samples with a very well known domain structure, namely (110)[001]FeSi3%. Permeability spectra μ(Iac,f,Hdc) were obtained in the frequency range (100u200aHz⩽f⩽100u200akHz), probe current range (0.1⩽Iac⩽50u200amA) and dc magnetizing field range (0⩽Hdc⩽500u200aOe). It is shown that the method developed in this article can be efficiently used to identify and study different dynamic processes driven by the probe current and controlled by the external dc field. In particular, it is shown that the method provides the tools to sepa...

High frequency magnetoimpedance in Ni81Fe19/Fe50Mn50 exchange biased multilayer

Gigahertz magnetoimpedance (MI) curves obtained in an exchange biased Ni81Fe19/Fe50Mn50 multilayer are reported. Experimental MI curves are shifted by the exchange bias field (HEB), following the features presented by the hysteresis curves. Theoretical MI curves, calculated using the classical expression for the impedance of a planar magnetic conductor, describe well the experimental data. The results open possibilities for application of exchanged biased MI multilayered materials for the development of autobiased linear magnetic field sensors.

Magneto-impedance effects in multilayered permalloy materials

The magneto-impedance (MI) effect has been studied in permalloy/Ag multilayers with different Ag thickness and number of bilayer. By increasing the Ag thickness from 7 to 25 A, the magnitude of the MI is greatly increased and the shape of the MI versus H curves evolves from a single-peak centered at H=0 to a double-peak structure. This is attributed to the different anisotropy axes induced by strain in the multilayers.

Wide frequency range magnetoimpedance in tri-layered thin NiFe/Ag/NiFe films: Experiment and numerical calculation

Given that the magnetoinductive effect (MI), skin effect and ferromagnetic resonance influence magnetic permeability behavior at different frequency ranges, the description of the magnetoimpedance effect over a wide range of frequency becomes a difficult task. To that end, we perform an experimental investigation of the magnetoimpedance effect in a tri-layered thin film over a wide frequency range. We compare the experimental results for a tri-layered thin film with numerical calculus performed using an approach that considers a magnetic transverse susceptibility model for planar systems and an appropriate magnetoimpedance model for a tri-layered system together. The results show remarkably good agreement between numerical calculus and experimental measurements. Thus, we discuss the experimental results in terms of different mechanisms that govern the MI changes observed in distinct frequency ranges and provide experimental support to confirm the validity of the theoretical approach.

Thickness dependence of the high-frequency magnetic permeability in amorphous Fe73.5Cu1Nb3Si13.5B9 thin films

Field-dependent transverse permeability characterization of amorphous thin films with nominal composition Fe73.5Cu1Nb3Si13.5B9 was performed for frequencies in the range of 100kHz–1.8GHz. Dynamic and static magnetic properties were investigated in films with thickness in the range from 21to5000nm. Samples with thicknesses below 85nm exhibit a well-defined in-plane uniaxial anisotropy and uniform ferromagnetic resonance modes. Samples thicker than 85nm were found to be magnetically isotropic in the plane, with complex magnetic dynamics depicted by several ferromagnetic resonance modes detected at relatively low fields. The results are discussed in terms of the stress contribution to the magnetic anisotropy of the samples.