Variation of structure and magnetic properties with thickness of thin Co59Fe26Ni15 films

Variations of phase composition and magnetic properties of electrodeposited nanocrystalline Co-Fe-Ni films with film thickness in the range of 50-500 nm were analyzed. The samples were magnetically soft with coercivity in the range H-c = 2-20 Oe and uni axial magnetic anisotropy up to H-k = 20 Oe. It was found that H-c decreases and H-k increases with increasing film thickness. The BCC phase dominates at small film thickness up to about 80 nm and the FCC phase increases when the film growths to a larger thickness. The increase of FCC phase correlates with the improvement of the ultrasoft magnetic properties. © 2004 Elsevier B.V. All rights reserved

Soft magnetism in nitrided Fe93Ni4Cr3 and Fe94Ni4T2 cold-rolled alloys

The magnetic properties in relation with the structure of nitrided cold-rolled Fe93Ni4Cr3 and Fe94Ni4Ti2 were studied. Various low-temperature nitriding treatments were applied in order to obtain soft magnetic materials. We show that the magnetic anisotropy depends sensitively on the nitrogen content. The lowest value of the coercive force, H-C = 40 A/m was obtained for samples containing TiN precipitates. For the Cr contained samples, a concentration of 14% (FeNi)(4)N (gamma')-phase decreases H-C below values corresponding to the samples containing only CrN precipitates. We discuss the influence of the texture on the magnetic properties of samples containing only BCC alpha'-phase, a mixture of alpha' + gamma'-phase, or samples which have been cycled through the epsilon-phase. Although grain refinement is observed after cycling and an almost random orientation of the grains is obtained, the magnetic properties do not improve. This is due to the fact the grain size is still too large to lead to averaging out of the magnetic anisotropy. Moreover, the stress/strain distribution developed during the treatments hampers domain wall motion and leads to an increased coercivity. (C) 2002 Elsevier Science B.V. All rights reserved

Thermal stability of the in-plane magnetic anisotropy and the coercivity of nanocrystalline CoFeNi films

By choosing the right production parameters, in-plane, uniaxial anisotropy up to about 15 Oe (1250 J/m(3)) could be induced in electrodeposited layers of Co59Fe26Ni15. This compound consists of a mixture of FCC and BCC phases. The layers were magnetically soft and nanocrystalline with grain sizes of 10-15 nm. Magnetic and non-magnetic annealing was performed up to 450degreesC. By magnetic annealing the anisotropy could be increased while the coercivity decreased. A remarkable field-dependent structural effect was found: during magnetic annealing the X-ray diffraction yield from the FCC grains was diminishing, while this yield was growing during non-magnetic annealing. From this we conclude that the domains were small. (C) 2003 Elsevier B.V. All rights reserved

On the GHz frequency response in nanocrystalline FeXN ultra-soft magnetic films

The periodicity and angular spread of the in-plane magnetization for ultrasoft nanocrystalline FeZrN films were estimated from an analysis of the ripple structure, observed in Lorentz transmission electron microscopy (LTEM) images. The influence of the micromagnetic ripple on the ferromagnetic resonance (FMR) width is analyzed using an approach based on the Landau-Lifshitz equation. A strong dependence of the resonance width on the magnetic moment dispersion is predicted. To a large extent this particular aspect explains the high frequency response in some of our films.</p

Evolution of free volume in ultrasoft magnetic FeZrN films during thermal annealing

The thermal stability of nanocrystalline ultra-soft magnetic (Fe98Zr2)(1-x)N-x films with x=0.10-0.25 was studied using high-resolution transmission electron microscopy (HRTEM), positron beam analysis (PBA) and thermal desorption spectrometry (TDS). The results demonstrate that grain growth during the heat treatment is accompanied by an increase of the free volume, by nitrogen reallocation and desorption. All this can drastically deteriorate the ultrasoft magnetic properties. The desorption starts already at slightly elevated temperatures, below 100 degreesC. However, most of the nitrogen leaves the sample at a temperature above 500 degreesC.</p

Positron annihilation in gaseous nitrided cold-rolled FeNiTi films

Positron beam analysis (PBA) was performed on cold-rolled Fe0.94Ni0.04Ti0.02 foils, which were subjected to different thermal treatments in an atmosphere of a gas mixture of NH3+H-2 (nitriding). The nitriding of the samples in the alpha -region (alphaN) of Lehrer diagram for the Fe-N system produced a large decrease of the central part of the Doppler broadened annihilation gamma -peak (S-parameter) and an increase of the contribution to the wings of the peak (W-parameter). The effect was much more pronounced for the (x-nitrided samples than for samples annealed in vacuum at the same temperature. A reduction of the alphaN-samples by annealing in H-2-atmosphere brings the S-parameter to a higher value. Further nitriding of alphaN-samples in the gamma'-region (alphaN+gamma 'N) of the Lehrer diagram increases S and lowers the W-parameter compared with the alphaN-samples. The changes in S- and W-parameters are interpreted on the basis of the evolution of microstructure of the films during the processing