[Paper Review] Inelastic neutron scattering studies of YFeO$_3$

Steven Hahn, A. Podlesnyak+6 more|arXiv (Cornell University)|Sep 14, 2013

Magnetic and transport properties of perovskites and related materials4 citations

TL;DR

This study uses inelastic neutron scattering to investigate spin waves in YFeO3, employing a full four-sublattice model that accounts for both weak ferromagnetic and hidden antiferromagnetic orders. The analysis yields precise exchange coupling constants: J₁ = -4.23 ± 0.08 meV (nearest neighbors only) or J₁ = -4.77 ± 0.08 meV and J₂ = -0.21 ± 0.04 meV (including next-nearest neighbors), with excellent agreement between model and experiment across low- and high-energy branches, including an observed branch linked to hidden antiferromagnetic order.

ABSTRACT

Spin waves in the the rare earth orthorferrite YFeO$_3$ have been studied by inelastic neutron scattering and analyzed with a full four-sublattice model including contributions from both the weak ferromagnetic and hidden antiferromagnetic orders. Antiferromagnetic (AFM) exchange interactions of $J_1 = -4.23 \pm 0.08$ (nearest-neighbors only) or $J_1 = -4.77 \pm 0.08$ meV and $J_2 = -0.21 \pm 0.04$ meV lead to excellent fits for most branches at both low and high energies. An additional branch associated with the hidden antiferromagnetic order was observed. This work paves the way for studies of other materials in this class containing spin reorientation transitions and magnetic rare earth ions.

Motivation & Objective

• To understand the magnetic excitation spectrum of YFeO3, a model system with no spin reorientation transition, enabling clean study of Fe3+ spin dynamics.
• To determine the exchange interaction parameters (J₁, J₂) in the Fe3+ sublattice using inelastic neutron scattering.
• To identify and characterize contributions from both weak ferromagnetism and hidden antiferromagnetic order in the spin wave spectrum.
• To validate a full four-sublattice model that includes both symmetric and antisymmetric (Dzyaloshinsky-Moriya) exchange interactions.

Proposed method

• Inelastic neutron scattering was performed on polycrystalline YFeO3 at two energy scales to probe spin wave dispersion across low- and high-energy regimes.
• A four-sublattice model was applied, incorporating both nearest-neighbor (J₁) and next-nearest-neighbor (J₂) antiferromagnetic exchange interactions.
• The model included contributions from weak ferromagnetism (along c-axis) and hidden antiferromagnetism (along b-axis), as defined by symmetry analysis of the magnetic unit cell.
• Magnetic form factors and instrumental resolution were convoluted into the theoretical intensity calculations using a Gaussian resolution function derived from McStas Monte Carlo simulations.
• The resolution function was fitted to experimental data using a two-dimensional Gaussian model with parameters optimized for cuts along K and L directions in momentum space.
• Simulated intensities were binned and integrated over momentum space to match the experimental data reduction procedure, enabling direct comparison.

Experimental results

Research questions

• RQ1 What are the precise values of the nearest- and next-nearest-neighbor exchange coupling constants (J₁ and J₂) in YFeO3?
• RQ2 How well does a four-sublattice model including both weak ferromagnetic and hidden antiferromagnetic orders describe the observed spin wave dispersion?
• RQ3 Is there experimental evidence for a distinct spin wave branch associated with the hidden antiferromagnetic order in YFeO3?
• RQ4 How do the measured spin wave intensities compare with theoretical predictions when accounting for magnetic form factors and instrumental resolution?
• RQ5 Can the model accurately reproduce both low- and high-energy branches of the spin wave spectrum?

Key findings

• The best-fit exchange parameters are J₁ = -4.23 ± 0.08 meV when considering only nearest neighbors, or J₁ = -4.77 ± 0.08 meV and J₂ = -0.21 ± 0.04 meV when including next-nearest neighbors.
• The four-sublattice model including both weak ferromagnetic and hidden antiferromagnetic contributions provides excellent agreement with experimental spin wave dispersion across all measured energy and momentum ranges.
• An additional spin wave branch was observed that is attributed to the hidden antiferromagnetic order along the b-axis, confirming its presence in the spin excitation spectrum.
• The magnetic form factor and instrumental resolution were successfully modeled using a Gaussian convolution, enabling accurate comparison between theory and experiment.
• The model accurately captures the intensity distribution and dispersion of both low-energy and high-energy spin wave modes.
• The study establishes YFeO3 as a benchmark system for understanding spin dynamics in rare earth orthoferrites, particularly for materials with complex magnetic transitions.