J.A. González

Interdiffusion and magnetic properties of Gd1-xCox/Co multilayers

The interdiffusion process in Gd1-xCox/Co multilayered systems has been investigated, in several series of samples made by sputtering, with different values of the Co content in the alloy (x). Grazing-incidence x-ray profiles and the electrical resistivity, together with magnetic measurements at room temperature, allow us to monitor and quantify the interdiffusion between layers as well as their magnetic properties. It is shown that this interdiffusion occurs on increasing the Co content of the alloy layer up to around 60% Co. In the x = 0.60 series the interdiffusion was found to be negligible and therefore a very good structure was obtained, while the ferrimagnetic structure between layers is preserved. The improved multilayered structure obtained in this system could lead to the development of new technological applications.

Electrical resistivity and interdiffusion in Gd1−xCox/Co multilayers

The interdiffusion process between Gd and Co has been investigated in several series of multilayered films consisting of Co and different GdCo alloys (Gd1−xCox)/Co (x=0, 0.37, and 0.60). Grazing incidence x-ray profiles provided a preliminary insight into the structure of the samples. Electrical resistivity measurements were performed in a temperature range between 8 and 300 K. For the three series, the room temperature electrical resistivity shows a clear fall once a critical Co thickness is surpassed, which we interpret as due to the growth of pure polycrystalline Co between the alloy layers. A simple model allows us to quantify the amount of Co diffused into the alloy layer. The results will be discussed considering the possible decrease of interdiffusion effects when Co is deposited onto the more stable GdCo alloys. This leads to a well defined multilayered structure, something that is essential for practical applications and for the theoretical study of its underlying physics.

On the relevance of Kondo disorder in the non-Fermi-liquid behavior of UCu4Ni

The electrical, magnetic and thermal properties of UCu4Ni show temperature dependencies suggestive of non-Fermi-liquid (NFL) behavior. In this work, we present an interpretation of these properties in terms of a Kondo disorder model for NFL behavior. The overall magnitude and temperature dependence of the magnetic susceptibility and the specific heat are found to be consistent with this model, assuming reasonable values of the relevant parameters, the average Kondo temperature (TK), the Kondo coupling constant (λ) and the distribution width w. These results are discussed in comparison with those obtained for other NFL systems, as UCu4Pd and UCu3.5Pd1.5.

X-ray study of the interdiffusion and interfacial structure in ferrimagnetic Gd1-xCox/Co multilayers

The strong interdiffusion that takes place in the Gd/Co multilayered system greatly influences the structure, composition, and thus the magnetic properties of the layers. We have conducted grazing incidence x-ray scattering experiments using synchrotron radiation on Gd1−xCox/Co multilayers with x=0, 0.37 and x=0.60 to study the interdiffusion process that takes place and the interfacial structure that results. Probing the scattering vector normal to the surface (specular scattering) showed excellent multilayer growth for all samples. For alloyed Gd samples, good multilayer growth was observed with Co thickness down to below 6 A. Fits to the reflectivity data show a reduction in the thickness of the Co layer, significantly away from its nominal value. This effect was more exaggerated in the pure Gd sample (x=0). We have successfully modeled this by assuming a significant portion of the Co has interdiffused into the pure Gd layer. Off-specular scattering experiments show that the interface roughness was con...

Magnetic properties of thin film GdCoRe amorphous alloys

Abstract Thin film amorphous samples of (Gd 1- x Co x ) 1- y Re y (a-GdCoRe) have been grown using a RF sputtering system. In order to consider these ferrimagnetic a-GdCoRe alloys for application in bubble devices, we have studied the temperature dependence of the saturation magnetization ( M s ) and coercivity ( H c ) as a function of composition, in the concentration range 0.74 x y M s vs. T plots, compensation temperatures ( T comp ) have been determined for all samples. The temperature dependence of the coercivity ( H c vs. T ) displays the sharp maximum at the compensation temperature ( T comp ) that is characteristic of ferrimagnetic amorphous alloys. All the samples studied show perpendicular anisotropy. The effect of Re addition on the magnetic properties of a-GdCo alloys will be discussed in comparison to those of other elements, as Mo.