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

TL;DR

This study investigates the magnetoresistive properties of nanocrystalline Cu-based alloys processed by high-pressure torsion, revealing the formation of ferromagnetic particles and giant magnetoresistance effects enhanced by annealing.

Contribution

It demonstrates the fabrication of bulk CuFeCo and CuFeNi materials with granular giant magnetoresistance via severe plastic deformation and thermal treatments, highlighting microstructural and magnetic evolution.

Findings

Granular giant magnetoresistance observed in processed samples

Annealing improves magnetic and electrical properties

Highest resistivity drop in Cu62Fe19Ni19 after heat treatment

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 {\deg}C. Combining the results of classical microstructural studies and magnetic measurements, insights into the evolution of ferromagnetic particles are accessible.