In this work we study theoretically the ferromagnetic resonance in a spin-valve. For this purpose, we propose a phenomenological model for the density of Helmholtz free energy taking into account the magnetocrystalline anisotropy, shape anisotropy, interlayer exchange coupling and exchange bias. Considering this energy density we solve the Landau-Lifshitz equation in spherical coordinates and in the resonance condition. In this way, we obtain the dispersion relation and, as a consequence, the frequency versus the resonance field. These results are in good agreement with the literature. Additionally, we apply the model to the IrMn/Co/Ru/NiFe system and study the magnetic coupling interlayers, where the non-magnetic layer (Ru) has a thickness of 3.2 nm. The results indicate the existence of an antiferromagnetic coupling with a strength of couping of Jbl + 2Jbc = −4.3 erg/cm2.

Alloys Fe-Al in the compositions Al25Fe75, Al50Fe50 and Al75Fe25 were synthesized by the arc furnace technique and the thermally treating 6000C. X-ray diractogram (XRD) and Mössbauer spectroscopy (MS) show the formation of the solid solution Fe(Al) rich and poor in aluminion. Tn the process of mechanical grinding to 10 hours milling maghemite γ − Fe2O3(Al) for compositions Al25Fe75 and Al50Fe50 with aluminiun atoms occupy some iron sites. In the case of the composition Al75Fe25 a single intermetallic Al13Fe4 is observed, remaining structurally invariant for all time nanostructuring.

Ferromagnetic resonance (FMR) study of quasiperiodic Au/Co Fibonacci multilayers revealed that uniform resonance modes related to the bulk Co and interface Au/Co regions of Co layers were excited in all multilayers. Paramagnetic and spin-wave resonance (SWR) modes also were observed into multilayers associated to higher order Fibonacci sequence. The FMR results show that there is no direct correlation between the number of absorption modes and the number of magnetic layers or the Fibonacci generation sequence of the quasiperiodic structure. Analysis of SWR modes revealed an interlayer effective coupling constant higher than that known for conventional Au/Co multilayers.

This work has been partially supported by the Brazilian agencies CNPq and CAPES. H.S.T. thanks to the Peruvian Doctoral Scholarship of CIENCIACTIVA (CONCYTEC) under Grant #218-2014-FONDECYT. C.V.L. and J.Q-M are grateful to CIENCIACTIVA (CONCYTEC) for financial support throught the Excellence Center Programs. We also acknowledge E.B. Saitovitch and CBPF for experimental facilities.

In this work, we study the synthesis process and structural and magnetic characterization of the ?-Al5Fe2 intermetallic alloy obtained by the arc-melting technique. Subsequently, in order to obtain homogeneous crystalline phase, all melted samples were annealed at 847?C during 2 days, and then quenched into water. The structural and micro-structural characterization of the samples were performed by X-ray diffraction and,57Fe transmission Mössbauer spectroscopy, while the morphological study was performed using scanning electron microscopy. Moreover, magnetic characterization was carried out using vibrating sample magnetometer. X-ray fluorescence was employed for elemental characterization. The results indicate that it is possible to employ the arc-melting technique to synthesize the ?-Al5Fe2 intermetallic phase with high structural quality: orthorhombic crystalline structure and Cmcm sp...

We have studied the resistance, magnetoresistance and Hall effect of AlCu2Mn Heusler alloy thin films prepared by flash evaporation on substrates cooled at 4He liquid temperature. The as-prepared samples were amorphous and were annealed stepwise to induce the transformation to the crystalline phase. The amorphous phase is metastable up to above room temperature and the transition to the crystalline phase was observed by means of resistance measurements.

This work has been partially supported by the Brazilian agencies CNPq and FAPERJ. H. S. T. thanks to the Peruvian Doctoral Scholarship Program of CIENCIACTIVA (CONCYTEC) for financial support under Grand #218-2014-FONDECYT. J. Q-M and C. V. L. are grateful to CIENCIACTIVA (CONCYTEC) for partial financial support through the Excellence Center Programs. J. Q-M is also grateful to the GEMaC Laboratory, for the hospitality during the preparation of this manuscript. In addition, E. B. S. acknowledges support from FAPERJ through several grants including Emeritus Professor fellow and CNPq for BPA and corresponding grants.

En la actualidad los peloides constituyen uno de los recursos naturales de gran potencial terapéutico. Este trabajo trata de la caracterización de tres muestras tomadas de un sitio ubicado en Chiica, alrededor de 60 Km al sur de la ciudad de Lima. Las técnicas experimentales empleadas en este estudio fueron: difracción de rayos X (DRX) espectroscopia Mössbauer por transmisión (EMT), microscopía electrónica de barrido (MEB) y los análisis físico-químicos. Los resultados obtenidos por DRX exhiben en general que la muestra MLG presenta fases asociadas con los minerales Vermiculita, Calcita, Cuarzo, Illita y Montmorillonita (Bentonita). En la muestra MLGC se observa las fases asociadas a los minerales Cuarzo, Sepioiita, Kaolinita y Calcita. Por EMT a temperatura ambiente (RT) se observó que la muestra MLG presenta tres dobletes cuadrupolares asociados con sitios de Fe presentes e...

Fe 50 Ni 50 alloy powder was prepared by milling the 1:1 stoichiometric mixture of Fe and Ni high purity elements using high energy vibrational ball-mill. Final powdered material was obtained directly after 30 h of milling process and the Rietveld analysis of the X-ray diffraction pattern of the sample reveals the presence of two Fe–Ni phases: the disordered ?–(Fe 45 Ni 55 ) alloy, with 91% of total fraction of the material (Fe–Ni solid solution plus grain boundary regions) and the chemically-ordered FeNi phase (9%), with L1 0 tetragonal structure. Average grain sizes of these Fe–Ni phases are respectively 60 nm and 20 nm. Results of extended X-ray absorption fine structure of Ni and Fe as well as 57 Fe Mössbauer spectroscopy also suggest the presence of atomically ordered FeNi phase. Mössbauer data have also shown that both Fe–Ni phases are magnetically ordered at room tempe...

H.S.T. thanks the Peruvian Doctoral Scholarship Program of CIENCIACTIVA (CONCYTEC) for financial support under Grand No. 218-2014-FONDECYT. J.Q.-M. and C.V.L. are grateful to CIENCIACTIVA (CONCYTEC) for financial support through the Excellence Centers Program. C.H.W.B. acknowledges financial support from EPSRC (Grant No.EP/J00412X/1). R.M. thanks to Institute Jean Lamour Nancy for financial support of visiting professorship. This work was supported by Ministry of Education and Science of the Russian Federation (grant 3.1992.2017/4.6). This work was also partly supported by the French PIA project “Lorraine Université d’Excellence,” reference ANR-15-IDEX-04-LUE. by the ANR-NSF Project, ANR-13-IS04-0008-01, COMAG. This work was also partly funded by the ANRT, under the CIFRE convention No. 2016/1458.