Magnetic properties of the Fe$_5$SiB$_2$-Fe$_5$PB$_2$ system

TL;DR

This study investigates the magnetic properties of Fe$_5$Si$_{1-x}$P$_{x}$B$_2$ compounds, revealing how composition affects Curie temperature, saturation magnetization, and anisotropy, combining experimental measurements with theoretical calculations.

Contribution

It provides new experimental data and theoretical insights into how phosphorus substitution influences magnetic properties in Fe$_5$SiB$_2$-Fe$_5$PB$_2$ system.

Findings

Saturation magnetization decreases with increasing P content.

Curie temperature peaks at x=0.1 and decreases thereafter.

Magnetocrystalline anisotropy increases with phosphorus concentration.

Abstract

The magnetic properties of the compound Fe$_5$Si$_{1-x}$P$_{x}$B$_2$ have been studied, with a focus on the Curie temperature $T_\textrm{C}$, saturation magnetization $M_\textrm{S}$, and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine $T_\textrm{C}\left(x\right)$ and $M_\textrm{S}\left(x\right)$. The saturation magnetization at 10 K (300 K) is found to monotonically decrease from $1.11~\mathrm{MA/m}$ ($1.03~\mathrm{MA/m}$) to $0.97~\mathrm{MA/m}$ ($0.87~\mathrm{MA/m}$), as $x$ increases from zero to one. The Curie temperature is determined to be 810 K and 615 K in Fe$_5$SiB$_2$ and Fe$_5$PB$_2$, respectively. The highest $T_\textrm{C}$ is observed for $x=0.1$, while it decreases monotonically for larger $x$. The Curie temperatures have also been theoretically determined to be 700 K and 660 K for Fe$_5$SiB$_2$ and Fe$_5$PB$_2$, respectively, using a combination of density functional theory and Monte Carlo simulations. The magnitude of the effective magnetocrystalline anisotropy was extracted using the law of approach to saturation, revealing an increase with increasing phosphorus concentration. Low--field magnetization vs. temperature results for $x = 0, 0.1, 0.2$ indicate that there is a transition from easy--axis to easy--plane anisotropy with decreasing temperature.