The magnetic properties of ${\mathrm{Cu}}_{97}{\mathrm{Co}}_3$ and ${\mathrm{Cu}}_{90}{\mathrm{Co}}_{10}$ granular alloys were measured over a wide temperature range $(2–300\mathrm{K})$. The measurements show an unusual temperature dependence of the coercive field. A generalized model is proposed and explains well the experimental behavior over a wide temperature range. The coexistence of blocked and unblocked particles for a given temperature raises difficulties that are solved here by introducing a temperature dependent blocking temperature. An empirical factor gamma $\left(\gamma \right)$ arises from the model and is directly related to the particle interactions. The proposed generalized model describes well the experimental results and can be applied to other single-domain particle system.

This paper reports an XPS surface study of pure phase BiFeO${}_3$ thin film produced and later etched by pure argon ions. Analysis of high-resolution spectra from Fe $2p$, Bi $4f$ and $5d$, O $1s$, and the valence band, exhibited mainly Fe${}^{3+}$ and Bi${}^{3+}$ components, but also reveal Fe${}^{2+}$. High-energy argon etching induces the growth of Fe${}^{\left(0\right)}$ and Bi${}^{\left(0\right)}$ and an increment of Fe${}^{2+}$, as expected. The BiFeO${}_3$ semiconductor character is preserved despite the oxygen loss, an interesting aspect for the study of the photovoltaic effect through oxygen vacancies in some ceramic films. The metal-oxygen bonds in O $1s$ spectra are related only to one binding energy contrary to the split from bismuth and iron reported in other works. All these data evidence that the low-pressure argon atmosphere is proved to be efficient to produce pure phase BiFeO${}_3$, even after argon etching.

Magnetic properties and changes of impedance upon external field (MI) are studied in amorphous CoP magnetic layers obtained by galvanostatic electrodeposition over cylindrical Cu substrates. The magnetic layer thickness is controlled by deposition time and varies between 3 and 7 μm. Due to the columnar growth of Co, thicker layers have stronger perpendicular radial anisotropy. The field and frequency dependence of the impedance is measured in the kHz/MHz range. Although it is generally accepted that a radial anisotropy should be unfavorable to the MI effect, an increase of the MI ratio with the thickness of the magnetic layer, and thus with anisotropy, is observed. Results are explained in terms of a model considering the current distribution along the sample thickness with two well-defined regions having different transport and magnetic properties.

Recent results concerning the giant magneto-impedance effect, GMI, in magnetic microwires having diameter in the range of a few micrometers and heterogeneous character are introduced in this work. Two types of microwires have been studied, namely, (i) magnetic microwires covered by insulating Pyrex glass coating and (ii) copper wires covered by electrodeposited magnetic microtubes. The magnetic anisotropy distribution in each type of microwire is correlated with giant magneto-impedance. While the main source of anisotropy in glass coated microwires is of magnetoelastic origin created by the stresses induced during quenching and by the coating, in the case of the microtubes the origin is the columnar growth during the electrodeposition. The influence on GMI of various treatments that modify the anisotropy is analyzed. Heterogeneous microwires with different thicknesses of insulating coating and of magnetic tube are analyzed.