Phase separation inCu90Co10high-magnetoresistance materials

Abstract

The relation between giant magnetoresistance ͑GMR͒ and phase separated nanostructures in Cu 90 Co 10 is studied using magnetotransport measurements together with transmission electron microscopy and x-ray microanalysis. The samples were melt-spun ribbons isochronally annealed up to 873 K, and all show in their grains a homogeneous spinodal decomposition characterized by long parallel Co-excess stripes. These stripes have 40-nm modulation periods and develop along the crystalline directions of each grain. Different anneals do not change appreciably the observed microstructures, while the magnetoresistance is initially enhanced by a factor of 2, followed by a 35% drop above 823 K. The latter coincides with the observation of a secondary lamellar decomposition of 4 nm modulation length. We propose that the GMR effects in CuCo alloys originate from these nanoscopic modulations of the constituents induced by nonequilibrium processes.

Phase separation of a supersaturated nanocrystalline Cu–Co alloy and its influence on thermal stability

“…In addition, it has been shown that in Cu90Co10 alloys, a spinodal type decomposition of the formed supersaturated solid solutions occurs after annealing at elevated temperatures [32,33].…”

“…Below 400°C the solubility of Co in Cu (and vice versa) is negligible [28]. Homogeneous Cu-Co alloys with supersaturations far from equilibrium can be produced by ball milling [29,30], sputtering [31], melt-spinning [32] and rapid quenching [33].…”

“…[31] found that the giant magnetoresistance effect can be observed in Cu-Co alloys with a granular structure composed of nanometer sized Co precipitates dispersed in the nonmagnetic Cu matrix. Later on, it was proposed that the giant magnetoresistance effect in Cu-Co alloys originate from modulated microstructures evolving from a homogeneous spinodal decomposition inside the grains in melt-spun ribbons [32].…”

“…[11]). In comparison with other processing techniques [29][30][31][32][33], the HPT process has certain advantages as the alloying process proceeds in the solid state.…”

Magnetic-field-induced phase separation via spinodal decomposition in epitaxial manganese ferrite thin films

“…It is fascinating that the spontaneously formed periodic structure influences the band gap, transport, and optical properties of the semiconductor alloys [6]. Additionally, periodically formed ferromagnetic alloys after SD wherein a magnetically ordered phase is embedded in a non-magnetic matrix is a very promising structure for device applications because giant magnetoresistance and other collective properties were observed, and thus has important implications for device design [6–8]. SD is a general phenomenon observed in various systems, such as alloys, glasses, and oxides.…”