Structure and giant magnetoresistance of granular Co-Cu nanolayers prepared by cross-beam PLD

TL;DR

This study investigates the structure and giant magnetoresistance of granular Co-Cu nanolayers prepared by cross-beam pulsed laser deposition, revealing tunable grain sizes, phase composition, and significant magnetoresistance effects influenced by thermal treatment.

Contribution

It provides new insights into the structural evolution, phase formation, and magnetoresistance properties of Co-Cu nanolayers fabricated by cross-beam PLD, including the effects of annealing.

Findings

Grain sizes of about 10 nm in as-deposited films.

Giant magnetoresistance of 1-2.3% observed, maximized after annealing at 725 K.

Thermal treatment increases grain size up to 100 nm, affecting magnetic properties.

Abstract

A series of Co_xCu_{100-x} (x = 0, 40...75, 100) layers with thicknesses in-between 13 nm and 55 nm were prepared on silicon substrates using cross-beam pulsed laser deposition. Wide-angle X-ray diffraction (WAXRD), transmission electron microscopy (TEM) and electrical transport measurements revealed a structure consisting of decomposed cobalt and copper grains with grain sizes of about 10 nm. The influence of cobalt content and layer thickness on the grain size is discussed. Electron diffraction (ED) indicates the presence of an intermetallic Co-Cu phase of Cu3Au structure-type. Thermal treatment at temperatures between 525 K and 750 K results in the progressive decomposition of Co and Cu, with an increase of the grain sizes up to about 100 nm. This is tunable by controlling the temperature and duration of the anneal, and is directly observable in WAXRD patterns and TEM images. A careful analysis of grain size and the coherence length of the radiation used allows for an accurate interpretation of the X-ray diffraction patterns, by taking into account coherent and non-coherent scattering. The alloy films show a giant magnetoresistance of 1...2.3 % with the maximum obtained after annealing at around 725 K.