High energy ion beam irradiation of Co NiFe Co Cu multilayers Effects on the structural, transport and magnetic properties

The aim of this work is to investigate the effects of 593 MeVAu irradiation using two different projectile charges, namely Au30 and Au46.3 on the structural, transport and magnetization properties of Co NiFe Co Cu multilayers. X Ray diffraction and extended X ray absorption fine structures measurements show no significant structural change for as deposited and irradiated multilayers. On the other hand, the magnetoresistance amplitude decreases with the ion fluence but it is insensitive to the projectile charge state. The correlation between changes in the magnetoresistance and remanent magnetization suggests that the main effect responsible for the decrease of the magnetoresistance is the creation of ferromagnetic pinholes. These results are discussed on basis of the electronic thermal spike model and nuclear cascades theory and show similarities to the effects observed at low energy ion beam irradiatio

Effects of Zn Substitution in the Magnetic and Morphological Properties of Fe-Oxide-Based Core-Shell Nanoparticles Produced in a Single Chemical Synthesis

Magnetic, compositional, and morphological properties of Zn-Fe-oxide core-shell bimagnetic nanoparticles were studied for three samples with 0.00, 0.06, and 0.10 Zn/Fe ratios, as obtained from particle-induced X-ray emission analysis. The bimagnetic nanoparticles were produced in a one-step synthesis by the thermal decomposition of the respective acetylacetonates. The nanoparticles present an average particle size between 25 and 30 nm as inferred from transmission electron microscopy (TEM). High-resolution TEM images clearly show core-shell morphology for the particles in all samples. The core is composed by an antiferromagnetic (AFM) phase with a Wüstite (Fe1-yO) structure, whereas the shell is composed by a ZnxFe3-xO4 ferrimagnetic (FiM) spinel phase. Despite the low solubility of Zn in the Wüstite, electron energy-loss spectroscopy analysis indicates that Zn is distributed almost homogeneously in the whole nanoparticle. This result gives information on the formation mechanisms of the particle, indicating that the Wüstite is formed first, and the superficial oxidation results in the FiM ferrite phase with similar Zn concentration than the core. Magnetization and in-field Mössbauer spectroscopy of the Zn-richest nanoparticles indicate that the AFM phase is strongly coupled to the FiM structure of the ferrite shell, resulting in a bias field (HEB) appearing below TNFeO, with HEB values that depend on the core-shell relative proportion. Magnetic characterization also indicates a strong magnetic frustration for the samples with higher Zn concentration, even at low temperatures