Magnetoresistive behaviour of ternary Cu-based materials processed by high-pressure torsion

Abstract

Severe plastic deformation using high-pressure torsion of ternary Cu-based materials (CuFeCo and CuFeNi) was used to fabricate bulk samples with a nanocrystalline microstructure. The goal was to produce materials featuring the granular giant magnetoresistance effect, requiring interfaces between ferro- and nonmagnetic materials. This magnetic effect was found for both ternary systems; adequate subsequent annealing had a positive influence. The as-deformed states, as well as microstructural changes upon thermal treatments, were studied using scanning electron microscopy and X-ray diffraction measurements. Deducing from electron microscopy, a single-phase structure was observed for all as-deformed samples, indicating the formation of a supersaturated solid solution. However, judging from the presence of the granular giant-magnetoresistive effect, small ferromagnetic particles have to be present. The highest drop in room temperature resistivity (2.45% at 1790 kA/m) was found in Cu62Fe19Ni19 after annealing for 1 h at 400 °C. Combining the results of classical microstructural studies and magnetic measurements, insights into the evolution of ferromagnetic particles are accessible.

Magnetic Materials via High-Pressure Torsion of Powders

“…[121,122] Binary and ternary powder mixtures consisting of different compositions of elemental Cu, Co, Ni and Fe were thus processed by HPT-deformation and examined as possible candidates for the granular GMR effect. [123][124][125] In these studies, it could be shown that it is possible to produce HPTdeformed samples showing GMR behavior at room temperature. The GMR-ratio is small compared to multilayer systems already in application.…”