Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Data-driven design of a new class of rare-earth free permanent magnets

Alena Vishina, Daniel Hedlund, Vitalii Shtender, Erna K. Delczeg-Czirjak, Simon R. Larsen, Olga Yu. Vekilova, Shuo Huang, Levente Vitos, Peter Svedlindh, Martin Sahlberg, Olle Eriksson, Heike C. Herper

TL;DR

This work demonstrates a data‑driven approach to discovering rare‑earth‑free permanent magnets by integrating high‑throughput DFT screening with experimental synthesis and characterization. The authors identify Co$_3$Mn$_2$Ge as a promising MgZn$_2$‑type magnet with predicted $M_S=1.71$ T, $K_U\approx1.44$ MJ/m^3, and $T_C\approx700$ K, and validate key magnetic properties experimentally while revealing a pronounced disorder‑induced easy‑cone anisotropy. Ab initio analysis shows that chemical disorder on Co–Ge sites reduces MAE and shifts magnetic behavior, while ordered variants recover higher MAE and $T_C$, suggesting routes to optimization via improved ordering; Ge substitution by neighboring elements indicates Co$_3$Mn$_2$Al and Co$_3$Mn$_2$Ga as additional promising RE‑free magnets. The study thus presents a coherent path from data mining to synthesis and demonstrates a new class of rare‑earth‑free magnets based on $T_3$Mn$_2$X MgZn$_2$ structures, with clear implications for tuning $M_S$, MAE, and $T_C$ through disorder control and chemical substitution.

Abstract

A new class of rare-earth-free permanent magnets is proposed. The parent compound of this class is Co$_3$Mn$_2$Ge, and its discovery is the result of first principles theory combined with experimental synthesis and characterisation. The theory is based on a high-throughput/data-mining search among materials listed in the ICSD database. From ab-initio theory of the defect free material it is predicted that the saturation magnetization is 1.71 T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m$^3$, and the Curie temperature is 700 K. Co$_3$Mn$_2$Ge samples were then synthesized and characterised with respect to structure and magnetism. The crystal structure was found to be the MgZn$_2$-type, with partial disorder of Co and Ge on the crystallographic lattice sites. From magnetization measurements a saturation polarization of 0.86 T at 10 K was detected, together with a uniaxial magnetocrystalline anisotropy constant of 1.18 MJ/m$^3$, and the Curie temperature of $T_{\rm C}$ = 359 K. These magnetic properties make Co$_3$Mn$_2$Ge a very promising material as a rare-earth free permanent magnet, and since we can demonstrate that magnetism depends critically on the amount of disorder of the Co and Ge atoms, a further improvement of the magnetism is possible. From the theoretical works, a substitution of Ge by neighboring elements suggest two other promising materials - Co$_3$Mn$_2$Al and Co$_3$Mn$_2$Ga. We demonstrate here that the class of compounds based on $T_3$Mn$_2$X (T = Co or alloys between Fe and Ni; X=Ge, Al or Ga) in the MgZn$_2$ structure type, form a new class of rare-earth free permanent magnets with very promising performance.

Data-driven design of a new class of rare-earth free permanent magnets

TL;DR

This work demonstrates a data‑driven approach to discovering rare‑earth‑free permanent magnets by integrating high‑throughput DFT screening with experimental synthesis and characterization. The authors identify CoMnGe as a promising MgZn‑type magnet with predicted T, MJ/m^3, and K, and validate key magnetic properties experimentally while revealing a pronounced disorder‑induced easy‑cone anisotropy. Ab initio analysis shows that chemical disorder on Co–Ge sites reduces MAE and shifts magnetic behavior, while ordered variants recover higher MAE and , suggesting routes to optimization via improved ordering; Ge substitution by neighboring elements indicates CoMnAl and CoMnGa as additional promising RE‑free magnets. The study thus presents a coherent path from data mining to synthesis and demonstrates a new class of rare‑earth‑free magnets based on MnX MgZn structures, with clear implications for tuning , MAE, and through disorder control and chemical substitution.

Abstract

A new class of rare-earth-free permanent magnets is proposed. The parent compound of this class is CoMnGe, and its discovery is the result of first principles theory combined with experimental synthesis and characterisation. The theory is based on a high-throughput/data-mining search among materials listed in the ICSD database. From ab-initio theory of the defect free material it is predicted that the saturation magnetization is 1.71 T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m, and the Curie temperature is 700 K. CoMnGe samples were then synthesized and characterised with respect to structure and magnetism. The crystal structure was found to be the MgZn-type, with partial disorder of Co and Ge on the crystallographic lattice sites. From magnetization measurements a saturation polarization of 0.86 T at 10 K was detected, together with a uniaxial magnetocrystalline anisotropy constant of 1.18 MJ/m, and the Curie temperature of = 359 K. These magnetic properties make CoMnGe a very promising material as a rare-earth free permanent magnet, and since we can demonstrate that magnetism depends critically on the amount of disorder of the Co and Ge atoms, a further improvement of the magnetism is possible. From the theoretical works, a substitution of Ge by neighboring elements suggest two other promising materials - CoMnAl and CoMnGa. We demonstrate here that the class of compounds based on MnX (T = Co or alloys between Fe and Ni; X=Ge, Al or Ga) in the MgZn structure type, form a new class of rare-earth free permanent magnets with very promising performance.

Paper Structure

This paper contains 24 sections, 2 equations, 21 figures, 9 tables.

Table of Contents

  1. Introduction
  2. High-throughput and data-mining search
  3. Experimental results
  4. Synthesis and structural characterisation
  5. Experimental magnetism
  6. Disordered Co$_3$Mn$_2$Ge
  7. Chemical substitution of Ge
  8. Discussion and conclusions
  9. Methods
  10. High-throughput DFT
  11. Synthesis
  12. Crystal structure analysis
  13. Magnetic measurements
  14. Acknowledgement
  15. Contributions
  16. ...and 9 more sections

Figures (21)

  • Figure 1: (Color online) Refined powder diffraction data of the synthesized Co$_{52}$Mn$_{34}$Ge$_{14}$ alloy. Observed (Y$_{obs}$), calculated (Y$_{calc}$), difference (Y$_{obs}$-Y$_{calc}$) diffraction profiles and Bragg’s peaks positions for Co$_{3}$Mn$_{2}$Ge (95.4 wt.%) and CoMn (4.6 wt.%) phases are shown.
  • Figure 2: (Color online) Magnetization of Co$_3$Mn$_2$Ge as a function of temperature in applied magnetic fields of $\mu_0$H = 0.01 T (white open circles and white open rectangles) and $\mu_0$H = 1 T (red filled rectangles). The inset shows the Curie-Weiss fit for the inverse magnetic susceptibility with $T_{\rm C}=359$ K. The cusp in $\mu_0$H = 1 T and drop in magnetization around 175 K is attributed to a spin--reorientation ($T_{srt}$).
  • Figure 3: (Color online) (a) Magnetization of a bulk powder of Co$_3$Mn$_2$Ge, as a function of magnetic field at 10 K, 70 K, 170 K and 300 K. (b,c,d) Isothermal magnetization of single crystals of Co$_3$Mn$_2$Ge at 300 K, 200 K and 100 K. Filled symbols show measurements where the magnetic field is perpendicular ($\bot$) to the crystallographic c--axis whereas open symbols show measurements with the magnetic field parallell ($\parallel$)with the c--axis.
  • Figure 4: (Color online) Approach to saturation plotted as the magnetization normalized with the value measured at 5 T as a function of inverse applied field squared for the bulk sample of Co$_3$Mn$_2$Ge.
  • Figure 5: (Color online) Ordered Co$_3$Mn$_2$Ge (as per ICSD) with Co atoms occupying 6 h (light red balls), Mn atoms taking 4 f (violet balls), and Ge (grey balls) occupying 2 a atomic sites (top); and the disordered Co$_3$Mn$_2$Ge structure obtained experimentally with 50-50% intermixing between the Co and Ge sites (bottom).
  • ...and 16 more figures