Microstructure-Controlled Magnetic Properties of Annealed FeCo Nanowires: The Key Role of Crystallinity and Defects

Abstract

The magnetic properties of FeCo nanowires are determined by their microstructure. By annealing as-deposited nanowires in reductive and oxidative atmospheres, we obtain two distinct microstructural states: a highly crystalline FeCo alloy phase and a CoFe 2 O 4 spinel phase derived from complete transformation of the alloy. Compared with the as-deposited state, both structures show improved crystallinity and reduced defects, leading to enhanced magnetic performance. The spinel phase dramatically increases the parallel-direction coercivity ( H c ) from 257.61 Oe to 1197.27 Oe and achieves a remanence ratio ( M r / M s ) of 58.62%, whereas the alloy phase exhibits high switching consistency. To move beyond macroscopic characterization, we employ first-order reversal curve (FORC) analysis as a key diagnostic tool to quantitatively deconvolute the distinct magnetic interactions in two phase states. This approach reveals that the broadened interaction field distribution in the spinel phase originates from local microstructural inhomogeneities, providing a direct microscopic explanation for the observed enhancement in H c . These results establish a direct microstructure-property correlation, demonstrating that crystallinity enhancement and phase transformation are key to optimizing FeCo nanowires for planar integrated devices.