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Coercivity analysis in sputtered Sm–Co thin films

Hard nanocrystalline Sm–Co thin films having a thickness of 500 nm have been prepared by heat-treating magnetron sputtered amorphous samples deposited over a 300 nm Cr buffer layer onto room temperature water cooled Si substrates. The thermal treatments resulted in the nanocrystallization of the precursor films and in the development of room temperature coercivities covering a range going from a few kOe, measured in the samples treated at low temperature, up to some tens of kOe, observed in the case of the films annealed at high temperatures (the room temperature coercivity of the sample treated at 825 K was 26 kOe). Our analysis of the influence of the thermal treatments on the particularities of the reversal process was based on the measurement of the temperature dependence of the coercive force. It was carried out in the framework of the micromagnetic model, which allowed us to evaluate two parameters accounting for the local anisotropy reduction and the magnitude of the local dipolar fields, respectiv...

Magneto-mechanical rotation of magnetostrictive amorphous wires

The mechanical rotation of both positive (FeSiB) and negative (CoSiB) magnetostrictive rapidly quenched amorphous wires, when submitted to an alternating axial magnetic field (Hac) with a frequency of a few kHz, has been investigated. Hac was varied from a few A/m to around 21 kA/m and a laser-based method was implemented to accurately determine the wire rotation frequencies. The appearance of such effect was found to be directly related with both the magnetostrictive nature of these materials and the diameter of the inner tube of the alternating current coil, φ, in which the wires were placed. A dynamical equilibrium of the effect of rotation was only reached for small values of φ. Different frictional arrangements yielded modifications of the spectrum obtained on plotting exciting frequency versus wire rotation frequency (typically several tens of Hz). When rotation started, a directionally controlled axial direct current magnetic field was applied, which eventually made the wires stop rotating. Accordi...

Eddy current damping of planar domain wall in bistable amorphous wires

An exact formula for the field produced by the eddy currents induced by transverse movements of a longitudinal planar domain wall in a magnetic cylinder is obtained. The result has been extended to satisfy the situation of bistable iron‐rich amorphous wires and compared with the dMav/dt pulse of such wires during magnetization reversal. It is shown that the propagating wall is essentially planar and the damping is solely due to eddy currents.

Anisotropy induced by the bowed-substrate sputtering technique in positive/negative magnetostriction FeB/CoSiB bilayers

CoSiB and FeB single layers and CoSiB/FeB bilayers with thicknesses ranging from 250 to 1500 A were grown on bowed glass substrates using rf sputtering. A magnetoelastic anisotropy was induced in the magnetic layers after removing the films from the sputtering chamber. The positive (FeB) and the negative (CoSiB) magnetostrictive single layers showed an easy magnetization axis transverse and parallel to the compression axis, respectively. The magnetic behavior of the CoSiB/FeB bilayers is shown to be extremely sensitive to the thickness of each layer, to their thickness ratios, and also to the deposition sequence of the layers on the substrate. These results are discussed in terms of the interactions between two magnetic phases with easy magnetization axes transverse to each other.

Practical model and calculation of AC resistance of long solenoids

In order to study the impedance of long solenoids, a tube model has traditionally been used. The model resistance is expressed in terms of the Bessel functions. We show how to relate the model resistance to the resistance of the actual solenoid, so that the model can be better used in practice. Since the computation accuracy when using the Bessel functions may decrease quickly with increasing the magnitude of their argument, the model results can be calculated only for thin solenoids at low frequencies. This problem has traditionally been solved by using the asymptotic expressions of Bessel functions. We show the appreciable error owing to this and propose a simple approach to make a very accurate correction. Practical formulas for the ac inductance of solenoids are also given.

CROSSED ANISOTROPIES IN FEB/COSIB BILAYERS INDUCED BY THE BOWED-SUBSTRATE SPUTTERING TECHNIQUE

FeB/CoSiB bilayers were deposited onto bowed glass substrates using the radio frequency sputtering technique. On removing the bilayers from the sputtering chamber, a magnetoelastic anisotropy was induced due to the compressive stress developed when the substrates recovered their initial planar shape. The bulk magnetic behavior was investigated using magnetometry techniques over a wide temperature range (5–350 K). The surface magnetism was analyzed using room-temperature Kerr magnetometry. Due to the positive/negative magnetostrictive nature of each of the layers deposited, the induced anisotropies are found to be crossed. Evidence of crossed anisotropies is obtained from the surface hysteresis loops as well as from the low-temperature thermomagnetic behavior.

Magnetic anisotropies in single and multilayered thin films grown by bowed-substrate sputtering

Thin-film structures composed of nearly nonmagnetostrictive single-layer Co/sub 76/Fe/sub 4/B/sub 20/ or magnetostrictive Fe/sub 80/B/sub 20/ and Co/sub 75/Si/sub 15/B/sub 10/ amorphous layers have been deposited on bowed glass substrates using the RF-sputtering technique. The fabrication procedure induces a postdeposition compressive stress in the thin-film structure when the sample is retrieved from an arching device in the sputtering chamber. This results in an induced magneto-elastic anisotropy that governs the magnetic easy axis of the film, depending on the sign of the magnetostriction constant of each layer. Particular attention is paid here to heterogeneous structures made of bi- or multilayers with magnetic easy axis oriented in a different direction in each layer. Bulk magnetic properties were evaluated from hysteresis loops and thermomagnetization measured by vibrating sample magnetometry (VSM) and quantum interference device (SQUID) magnetometry. Magnetic domain walls and out-of-plane magnetized domains were observed by a Kerr imaging system and magnetic force microscopy. The combination of microstructure and strains induced in the layers determines the orientation of the observed magnetic anisotropies, which vary from high in-plane anisotropies up to out-of-plane orientations for selected films. The results, which provide reassurance that effective anisotropies are induced in each of the layers, are discussed in terms of the interactions between magnetic phases with different induced easy magnetization axes.

Susceptibility spectrum of a magnetic conducting sphere

The frequency dependence of the complex ac susceptibility of a magnetic conducting sphere is derived. The resultant formulas can be used to determine electrical conductivity from ac susceptibility measurements, to calculate ac susceptibilities of standard samples for the calibration of ac susceptometers, and to analyze ac losses in materials research.

Influence of the interfaces on the anisotropic magnetoresistance of Ni/Co multilayers

Anisotropic magnetoresistance in Ni is found to increase abruptly when Co impurity layers are inserted. Some experiments carried out in different Ni/Co multilayers indicate that interfaces are responsible for the magnetoresistance enhancement.

Temperature dependence of the magnetization processes in Co/ Al oxide permalloy trilayers

The magnetization process of Co/Al oxide/Py trilayers and its evolution with the temperature have been analyzed. The particular behavior of the Co layers, including the shift of the hysteresis loops and a coercivity increase with the decrease of temperature, is related with the apparition of a CoO layer at the Co/Al-oxide interface.