The effect of annealing on magnetotransport and structural properties of Ni70Co30/Cu multilayers is investigated. The GMR signal remains stable up to 175 °C and almost disappears at 285 °C. The total resistivity of multilayers is nearly constant below 175 °C and rapidly increases after annealing at 285 °C. By the combination of x-ray reflectivity, x-ray diffuse scattering and extended x-ray absorption fine structure (EXAFS) techniques, it is found that Ni atoms and Cu atoms occupy preferentially the interfacial position of the multilayer and the interface roughness is mainly caused through the diffusion of Cu and Ni in the grain boundary during the deposition. After 285 °C annealing, the interface roughness increases remarkably and the interfacial lateral correlation length and the fractal exponent of Co, Ni and Cu decrease significantly. At the same time, the differences in the interfacial lateral correlation lengths of Co, Ni and Cu also becomes smaller. This suggests that the intermixing of adjacent layers takes place. It can be concluded that the degradation mechanism of the GMR effect on the annealed Ni70Co30/Cu multilayer is the compositional mixing at the interfaces, rather than the interlayer diffusion of atoms along the grain boundary.
We have successfully prepared the iron-based superconductor K0.8Fe2Se2 crystals (Tc=27 K) and studied the carrier transport properties along the c-axis in detail. Samples are characterized by XRD, SEM and temperature-dependent resistivity. The result shows that there is “phase separation” in the samples. Based on the experimental results, the iron-based superconductor is not a simple two phases alternating along the c-axis, but the metal phases should have weak-link channels along the c-axis, forming a nearly 3D special net mode. Studies of the thermal conductivity and the complex impedance spectrum z(omega, T0) suggest that the superconducting crystals have a lot of grain boundaries along the c-axis direction, the bound polarization charges result in relative dielectric constant of about 106 in magnitude and negative phase characteristics in the vicinity of 10 MHz.
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