Microstructural Changes Influencing the Magnetoresistive Behavior of Bulk Nanocrystalline Materials

TL;DR

This study investigates how microstructural modifications in bulk nanocrystalline ferromagnetic materials, induced by severe plastic deformation and thermal treatments, influence their giant magnetoresistive properties, revealing optimal annealing conditions for enhanced performance.

Contribution

It demonstrates the microstructural factors affecting magnetoresistance in nanocrystalline materials and identifies optimal thermal treatment conditions to improve their magnetoresistive behavior.

Findings

Giant magnetoresistance observed in as-deformed materials.

Thermal treatments can enhance magnetoresistive properties.

Optimal annealing temperature varies with material composition.

Abstract

Bulk nanocrystalline materials of small and medium ferromagnetic content were produced using severe plastic deformation by high-pressure torsion at roomtemperature. Giant magnetoresistive behavior was found for as deformed materials, which was further improved by adjusting the microstructure with thermal treatments. The adequate range of annealing temperatures was assessed with in-situ synchrotron diffraction measurements. Thermally treated CuCo materials show larger giant magnetoresistance after annealing for 1 h at 300C, while for CuFe this annealing temperature is too high and decreases the magnetoresistive properties. The improvement of magnetoresistivity by thermal treatments is discussed with respect to the microstructural evolution as observed by electron microscopy and ex situ synchrotron diffraction measurements.