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

Daniel Hedlund, Johan Cedervall, Alexander Edström, Mirosław Werwinski, Sofia Kontos Olle Eriksson, Ján Rusz, Peter Svedlindh, Martin Sahlberg, Klas Gunnarsson

TL;DR

This study investigates the Fe$_5$SiB$_2$-Fe$_5$PB$_2$ system across 0 ≤ x ≤ 1 to understand how substituting Si with P tunes high-temperature ferromagnetism and anisotropy. The authors combine temperature- and field-dependent magnetometry with density functional theory and Monte Carlo simulations to map $T_{ ext{C}}(x)$, $M_{ ext{S}}(x)$, and $|K_{ ext{eff}}|$, and to relate these properties to underlying exchange interactions. Key findings include a maximum experimental $T_{ ext{C}}$ near $x=0.1$, a monotonic decrease of $M_{ ext{S}}$ with increasing P content, and an MAE that grows with phosphorus content, with a zero-crossing predicted around $x ightarrow 0.7$ at zero temperature. The results show general agreement between experiment and theory and provide insights for tuning magnetic properties in pursuit of rare-earth-free permanent magnets.

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.

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

TL;DR

This study investigates the FeSiB-FePB system across 0 ≤ x ≤ 1 to understand how substituting Si with P tunes high-temperature ferromagnetism and anisotropy. The authors combine temperature- and field-dependent magnetometry with density functional theory and Monte Carlo simulations to map , , and , and to relate these properties to underlying exchange interactions. Key findings include a maximum experimental near , a monotonic decrease of with increasing P content, and an MAE that grows with phosphorus content, with a zero-crossing predicted around at zero temperature. The results show general agreement between experiment and theory and provide insights for tuning magnetic properties in pursuit of rare-earth-free permanent magnets.

Abstract

The magnetic properties of the compound FeSiPB have been studied, with a focus on the Curie temperature , saturation magnetization , and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine and . The saturation magnetization at 10 K (300 K) is found to monotonically decrease from () to (), as increases from zero to one. The Curie temperature is determined to be 810 K and 615 K in FeSiB and FePB, respectively. The highest is observed for , while it decreases monotonically for larger . The Curie temperatures have also been theoretically determined to be 700 K and 660 K for FeSiB and FePB, 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 indicate that there is a transition from easy--axis to easy--plane anisotropy with decreasing temperature.

Paper Structure

This paper contains 9 sections, 3 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experiment
  3. Sample preparation and material characterization
  4. Magnetization measurements
  5. Details of calculations
  6. Results and discussion
  7. Phase analysis
  8. Experimental and calculated magnetic results
  9. Conclusions

Figures (9)

  • Figure 1: Crystal structure of Fe$_5$Si$_{1-x}$P$_x$B$_2$.
  • Figure 2: Structure refinements performed on the samples (a) Fe$_5$SiB$_2$, (b) Fe$_5$Si$_{0.5}$P$_{0.5}$B$_2$ and (c) Fe$_5$PB$_2$. (d) shows the refined unit cell parameters as a function of phosphorous content. The secondary phases are Fe$_3$Si in (a) and (b) and Fe$_2$P in (c).
  • Figure 3: DTA scans used to extract the melting temperatures for the samples Fe$_5$SiB$_2$, Fe$_5$Si$_{0.5}$P$_{0.5}$B$_2$ and Fe$_5$PB$_2$.
  • Figure 4: $M$ vs. $H$ at 300 K from top to bottom for Fe$_5$SiB$_2$, Fe$_5$Si$_{0.5}$P$_{0.5}$B$_2$ and Fe$_5$PB$_2$. Insert shows the $M-H$--curve for Fe$_5$Si$_{0.5}$P$_{0.5}$B$_2$ at weak fields.
  • Figure 5: Experimental values for M$_{\mathrm{S}}$ at 300 K and 10 K together with previously reported values.Cedervall2016 Full substitution of Si for P decreases $M_{\mathrm{S}}$ from 1.03 MA/m (Fe$_5$SiB$_2$) to 0.87 MA/m (Fe$_5$PB$_2$) at 300 K. The dashed line is added as a guideline for the eye.
  • ...and 4 more figures