Enhancing Magnetostriction in Boron-doped Fe-Ga Alloys for Magnon-Phonon Hybrid Quantum System

Hybrid quantum systems offer promising opportunities for quantum information science by coherently interfacing excitations from different physical systems to combine complementary functionalities. Magnons, the collective spin excitations in magnetic materials, are particularly appealing due to their tunability and intrinsic nonreciprocity, enabling applications such as nonreciprocal quantum transduction and noise isolation in superconducting circuits. To enhance coherent magnon interactions, we develop magnetic materials with strong magnetoelastic coupling, focusing on low-damping magnetoelastic FeGaB alloys. These materials facilitate magnon-phonon hybrid systems for high-efficiency nonreciprocal microwave transduction with reduced insertion loss, which is crucial for quantum state transfer and entanglement. Using density functional theory, we investigate the microscopic origins of magnetostriction in FeGa alloys by comparing compositions in different structural phases: the ordered D03 phase (Fe₃Ga) and the disordered A2 phase (Fe_81.25Ga_18.75). We further examine the effects of boron doping in (Fe₈₀Ga₂₀)_1-xB_x with x=0.06 and 0.12, which disrupts the D0₃ phase. Our results show that boron doping enhances magnetostriction by destabilizing this unfavorable phase while maintaining low Gilbert damping, consistent with experimental observations in FeGaB films with an optimal B content of ~10% [1]. Analysis of the interatomic distances and spin- and orbital-resolved electronic properties reveals that boron synergistically enhances magnetostriction by introducing local strain, which in turn optimizes the electronic structure for a stronger magnetoelastic effect. Our results elucidate a materials design pathway that uses dopants to engineer structural disorder and tune electronic properties for the development of high-performance magnetoelastic alloys for quantum technologies.



[1] Z. Zhang et al., Phys. Rev. Materials 9, 074412 (2025)