Phonon-driven tuning of exchange interactions in Y3Fe5O12

Abstract

Yttrium iron garnet (Y3Fe5O12) is a prototypical ferrimagnetic insulator widely used in spin-wave and magnonic devices owing to its extremely low magnetic damping and long magnon propagation length, and recent experiments suggest that lattice vibrations can influence magnetic properties, motivating a microscopic understanding of how phonons modify exchange interactions. In this work, phonon-driven tuning of exchange interactions in Y3Fe5O12 is investigated from a mode-resolved perspective based on first-principles calculations. We focus on how optical phonons modify the dominant superexchange pathways and how lattice distortions affect the Fe-O-Fe bond geometry that governs the exchange interaction. To this end, phonon modes are computed from density functional theory, and the exchange interactions are evaluated from a Wannier-based tight-binding model and mapped onto a spin Hamiltonian, while displaced structures along individual infrared-active modes are used to quantify their impact on the magnetic interactions.

Figures (10)

• Figure 1: Crystal structure of Y$_3$Fe$_5$O$_{12}$. Octahedral $a$ sites and tetrahedral $d$ sites form two magnetic sublattices. The dominant $J_{ad}$ and additional $J_{dd}$ and $J_{aa}$ exchange paths are highlighted.
• Figure 2: Spin-resolved partial density of states (DOS) of Y$_3$Fe$_5$O$_{12}$ projected onto Fe $3d$ states for (a) $U = 0$ eV and (b) $U = 3$ eV. Contributions from Fe $a$ (octahedral, blue) and Fe $d$ (tetrahedral, orange) sites are shown together with the total density of states (black). Increasing $U$ shifts the Fe $3d$ states to lower energies and enhances the separation between O $2p$ and Fe $3d$ states. a
• Figure 3: Electronic band structure of ferrimagnetic YIG calculated along the high-symmetry path at the GGA level ($U=0$). Red and blue lines denote bands with opposite spin character.
• Figure 4: Calculated magnon dispersion of Y$_3$Fe$_5$O$_{12}$ with experimental data overlaid; red lines denote acoustic branches and blue lines denote optical branches. The experimental data points are taken from the literature and were reconstructed from published figures: The experimental data points are taken from the literature and were reconstructed from published figures: Plant Plant1977 (295 K, cyan filled squares; 83 K, orange filled diamonds), Shamoto et al.Shamoto2018 (295 K, unfilled circles), and Man et al.Man2017 (10 K, green filled circles).
• Figure 5: Phonon band structure calculated along the high-symmetry path $\Gamma$--H--N--$\Gamma$--P (left panel), together with the corresponding projected phonon density of states (DOS) (right panel, in arbitrary units). The projected DOS is resolved into atomic contributions from Y (black), Fe at the $d$ sites (orange), Fe at the $a$ sites (blue), and O (red).