Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.29386

First-principles modeling of ordering in Fe-rich Fe-Si alloys

Daniil M. Khodachenko·Andrei V. Ruban·Franco Moitzi·Oleg E. Peil·Vsevolod I. Razumovskiy
View original source ↗Read source document ↗Export metadata ↓

Abstract

The atomic ordering in Fe-rich Fe-Si alloys strongly influences their magnetic properties and mechanical behavior. While general features of long-range atomic ordering are known from the experimentally established phase diagram in this composition range, detailed atomic configurations and driving forces behind them remain speculative. Here, we address this gap by using effective cluster interactions (ECI) obtained from density functional theory (DFT) calculations and subsequent statistical thermodynamics modeling to unravel the interplay between magnetism, composition, and temperature in body-centered cubic (bcc) Fe-Si alloys up to 20 at% Si. Our analysis reveals that the ordering behavior is governed by a strong coupling between magnetic order, lattice expansion, and Si concentration, with specific ECI shells switching sign or magnitude as the magnetic state changes, which is reflected in the phase equilibria and ordering behavior of Fe-Si alloys. In particular, we demonstrate that D0$_3$ ordering is, in fact, primary in the totally ordered ferromagnetic state, while the B2 type of ordering is promoted in the paramagnetic state at elevated temperatures. The temperature-dependent evolution of these ordering patterns, obtained from Monte Carlo simulations based on the magnetically resolved ECIs, reproduces the experimentally observed phase equilibria and short-range order characteristics. By explicitly linking the magnetic state with the effective interactions and macroscopic phase behavior, this work establishes a predictive framework for an ab initio-based description of ordering in Fe-rich Fe-Si alloys and highlights the decisive role of magnetism in ordering phenomena in this system.

Explore related subjects

cond-mat.mtrl-sci

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Daniil M. Khodachenko, Andrei V. Ruban, Franco Moitzi, Oleg E. Peil, Vsevolod I. Razumovskiy. 2026-10-21. First-principles modeling of ordering in Fe-rich Fe-Si alloys. https://arxiv.org/abs/2610.29386

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Order-Disorder in Fe-Si Alloys: Implications for Seismic and Transport Properties of Earth's Inner Core

Understanding the structure and dynamics of Earth's inner core is essential for constraining its composition, thermal evolution, and seismic behavior. Silicon is widely considered a major light element in the core. Here, we use first-principles molecular dynamics and thermodynamic modeling to investigate the structural, elastic, and transport properties of iron-silicon (Fe-Si) alloys under inner-core conditions. By computing the Gibbs free energies of multiple solid phases, including ordered B2, hexagonal close-packed (hcp), face-centered cubic (fcc), and body-centered cubic (bcc) Fe-Si, we construct a phase diagram relevant to inner-core pressures and temperatures. We identify a pronounced miscibility gap between hcp and cubic Fe--Si phases, with phase coexistence over approximately 6--11 wt\% Si at 6000 K. The cubic phase exhibits a strong order-dependent elastic response, with disordered bcc showing a large intrinsic shear anisotropy (22.9\% at 6000 K), in contrast to the nearly isotropic hcp phase (0.6\%). Meanwhile, disordered bcc Fe--Si produces shear wave velocities ($V_S=3.73$ km$\cdot$s$^{-1}$) and Poisson's ratios comparable with seismological constraints. In addition, disordered bcc Fe--Si exhibits a lower thermal conductivity than hcp Fe--Si, providing a quantitative constraint on phase-dependent electronic heat transport. These results demonstrate that chemical ordering strongly controls the stability and physical properties of cubic Fe--Si alloys, and suggest that metastable or localized cubic Fe--Si phases may contribute to the structural and transport complexity of Earth's inner core.

cond-mat.mtrl-sci↗
arXiv2026

Dynamical Nonrelativistic Spin Splitting via THz Nonlinear Phononics

Nonrelativistic spin splitting (NRSS) in collinear antiferromagnets, including altermagnets and compensated ferrimagnets, offers a route to high-frequency spintronics immune to stray fields, but its dynamic control has remained elusive. We demonstrate, using density functional theory (DFT) and nonlinear phononics, that THz laser pulses can achieve ultrafast, reversible control of NRSS on picosecond timescales in antiferromagnets. We derive two mode-selection criteria, accounting for phonon and magnetic wavevector compatibility and inversion parity, to identify which phonon modes can activate NRSS. Our calculations illustrate the creation of NRSS in spin-degenerate NiO and the enhancement of existing splitting in LaFeO$_3$. While practical implementation depends on excitation conditions, lattice dynamics, and mode coupling, these results establish design principles for identifying materials with stronger and more accessible responses. Limitations imposed by driving fields, phonon damping, and anharmonic detuning motivate further materials screening based on accessible excitation strengths, lattice stability, resonance frequency matching, and favorable anharmonic coupling.

cond-mat.mtrl-sci↗
arXiv2026

Decoding Composition-Structure-Performance Relations in Sodium Layered Oxide Positive Electrode Materials

Layered sodium transition-metal (TM) oxides, Na$_x$TMO$_2$, are among the most promising sodium-ion positive electrode materials, yet their Na/vacancy orderings, layer stacking sequences, and cooperative Jahn--Teller distortions are known only for a few single-TM compounds. We compile the Na/vacancy orderings reported in earlier studies into a single library of 41 unique orderings and apply this uniformly to five single-TM and all ten Na$_x$TM$_{0.5}$TM$'_{0.5}$O$_2$ oxides (TM = Ti, Mn, Fe, Co, Ni), screening more than 120,000 structures with machine-learning interatomic potentials prior to 1,025 accurate first-principles calculations. The phase diagrams explain the observed O3/P3/O1 sequences and voltages, and the O3-to-P3 competition hinges on ordering energies of a few meV per atom that scalar descriptors, such as the cationic potential and the interlayer-slab distance, miss. Our extensive analysis reveals that the redox couples form a nearly partner-independent ladder, Ti$^{3+/4+}$ $<$ Mn$^{3+/4+}$ $<$ Co$^{3+/4+}$ $<$ Ni$^{2+/3+}$ $<$ Fe$^{3+/4+}$, explaining pristine charge transfer and the oxidation sequence. Van Vleck analysis of every TMO$_6$ octahedron reveals that TM mixing suppresses the cooperative Jahn--Teller distortions of Mn$^{3+}$ and Ni$^{3+}$ through charge transfer to Jahn--Teller-inactive states or dilution of Jahn--Teller-active centers. We formulate an energy-density-versus-strain map that yields a design rule: a high-voltage couple without Jahn--Teller strain, which Mn$^{4+}$/Ni$^{2+}$ charge transfer realizes in Na$_x$Mn$_{0.5}$Ni$_{0.5}$O$_2$, the most practical composition. We release the ordering-resolved dataset as a training set for subsequent training of accurate machine-learning interatomic potentials.

cond-mat.mtrl-sci↗