J.G.S. Duque

Large nonlinear magnetoimpedance in amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers

Fourier analysis of the nonlinear response of the impedance signal of amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers is presented. The harmonic components of the voltage signal present a strong asymmetry. A strong variation (around 1400%) of the second-harmonic signal (V2 f) as a function of the applied magnetic field is observed. Nonlinear effects and the asymmetric behavior in harmonics can be associated with the anisotropies induced during the fabrication process. These results can lead to improvement of the performance of future magnetoimpedance sensors.

Nonlinear giant magnetoimpedance and the asymmetric circumferential magnetization process in soft magnetic wires

The magnetoimpedance effect and its nonlinear terms are analysed for a (Co0.94Fe0.06)72.5Si12.5B15 amorphous wire. In order to enhance the nonlinear contribution the sample was previously subjected to current annealing (Joule heating) to induce a circumferential anisotropy. The effect of the application of a torsional strain on the nonlinear magnetoimpedance is analysed in terms of the torsional dependence of the magnetic permeability, evaluated through experimental circumferential hysteresis loops. The results obtained clearly confirm the direct correlation between the asymmetric circumferential magnetization process and the occurrence of nonlinear second-harmonic terms in the magnetoimpedance voltage.

Temperature dependence of coercive field of ZnFe2O4 nanoparticles

Structural and magnetic measurements on ZnFe2O4 nanoparticles obtained through co-precipitation chemical method are reported. The Rietveld analysis of X-ray patterns reveal that (i) our samples are single phase, and (ii) the average particle size increases with synthesis temperature. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements show that the average blocking temperature increases for increasing mean particle size. Besides, one can observe via magnetization measurements that our particle size distribution also increases as a function of synthesis temperature. Finally, we have observed that the coercive field does not decay with the square root of temperature following the Neel relaxation and the Bean-Livingston approaches. In order to fit our experimental data, we have used a generalized model that proposes a temperature dependence of blocking temperature due to the coexistence of blocked and unblocked particles. This proposed generalized model shows good agreement with our ...

Crystal structure and physical properties of Gd3Co4Sn13 intermetallic antiferromagnet

We have synthesized single crystalline samples of Gd3Co4Sn13 intermetallic compound using a Sn-flux method. This compound crystallizes with a cubic Yb3Co4Sn13-type structure, space group Pm-3n, which has 40 atoms per unit cell. Measurements of the magnetic susceptibility, heat capacity, electrical resistivity, and electron spin resonance (ESR) revealed that Gd3Co4Sn13 is a metallic Curie-Weiss paramagnet at high temperature and presents an antiferromagnetic ordering below TN=14.5K. In the paramagnetic state, a single Gd3+ ESR line with a nearly temperature independent g∼2.005(2) is observed, and its linewidth follows a Korringa-like behavior as a function of temperature. From the Korringa rate (ΔH∕ΔT∼4Oe∕K) and g-shift (Δg∼0.012) obtained from the ESR experiments combined with the magnetic susceptibility and specific heat data for Gd3Co4Sn13, we have extracted the exchange parameters between the Gd3+ local moments and the conduction-electrons (c-e) in this compound. This exchange parameter Jfs≈10meV was f...

Determination of the effective anisotropy constant of CoFe2O4 nanoparticles through the T-dependence of the coercive field

We present a systematic study of the coercive field of CoFe2O4–SiO2 nanocomposites. The samples were prepared via the sol-gel method by using the Tetraethyl Orthosilicate as starting reagent. Results of X-ray diffraction, transmission electron microscopy, and X-ray fluorescence confirm the dispersion of the magnetic nanoparticles inside the silica matrix. In addition, the shift in the maximum of Zero-Field-Cooled curves observed by varying the weight ratio of CoFe2O4 nanoparticles to the precursor of silica is consistent with the increasing of average interparticle distances. Because our samples present a particle size distribution, we have used a generalized model which takes account such parameter to fit the experimental data of coercive field extracted from the magnetization curves as a function of applied field. Unlike most of the coercive field results reported in the literature for this material, the use of this model provided a successful description of the temperature dependence of the coercive fi...

Electron spin resonance of Gd3+ in GdmMnIn3m+2n (M=Rh,Ir; n=0,1; m=1,2) antiferromagnets

We report electron spin resonance experiments of Gd3+ in the GdmMnIn3m+2n (M=Rh,Ir; n=0,1; m=1,2) intermetallic compounds. For T>TN∼45K, all compounds present a single Dysonian resonance and show a Korringa-like temperature dependence of the linewidth, ΔH=a+bT. The residual linewidth a is strongly affected by the transition metal M=Rh or Ir and/or by the layering (m=1 or 2) or change in structure (n=0,1). The residual linewidth is associated with an unresolved crystalline electrical field (CEF) fine structure. Consequently, a systematic evolution of the CEF in the GdmMnIn3m+2n compounds is inferred. A discussion to what extent our results can explain to the CEF effects observed in isostructural R-based compounds will be given.

Direct determination of the crystal field parameters of Dy, Er, and Yb impurities in the skutterudite compound CeFe 4 P 12 by electron spin resonance

Despite extensive research on the skutterudites for the last decade, their electric crystalline field ground state is still a matter of controversy. We show that electron spin resonance (ESR) measurements can determine the full set of crystal field parameters (CFPs) for the

Structurally tuned magnetic properties of TbmRhnIn3m+2n (m = 1,2; n = 0,1) intermetallic antiferromagnets

{T}_{h}

Influence of substrate on the magnetic properties of Ni and permalloy sub-micrometric patterned stripes

cubic symmetry

Electron spin resonance of Gd3+ in the intermetallic Gd1–xYxNi3Ga9 (0 ≤ x ≤ 0.90) compounds

(Im3)