Reinvestigation of the intrinsic magnetic properties of (Fe$_{1-x}$Co$_x$)$_2$B alloys and crystallization behavior of ribbons

TL;DR

This study investigates the magnetic anisotropy of (Fe$_{1-x}$Co$_x$)$_2$B alloys using experiments and first-principles calculations, revealing limitations of traditional theories and exploring crystallization behavior relevant for permanent magnet applications.

Contribution

It provides a combined experimental and theoretical analysis of magnetic properties and crystallization behavior of (Fe$_{1-x}$Co$_x$)$_2$B alloys, highlighting the inadequacy of standard models and offering new insights.

Findings

Anomalous temperature dependence of anisotropy constant observed.

First-principles calculations better explain experimental data.

Rapid crystallization of melt-spun ribbons demonstrated.

Abstract

New determination of the magnetic anisotropy from single crystals of (Fe$_{1-x}$Co$_x$)$_2$B alloys are presented. The anomalous temperature dependence of the anisotropy constant is discussed using the standard Callen-Callen theory, which is shown to be insufficient to explain the experimental results. A more material specific study using first-principles calculations with disordered moments approach gives a much more consistent interpretation of the experimental data. Since the intrinsic properties of the alloys with $x=0.3-0.35$ are promising for permanent magnets applications, initial investigation of the extrinsic properties are described, in particular the crystallization of melt spun ribbons with Cu, Al, and Ti additions. Previous attempts at developing a significant hysteresis have been unsuccessful in this system. Our melt-spinning experiment indicates that this system shows rapid crystallization.