Direct visualization of the impurity occupancy roadmap in Ni-substituted van der Waals ferromagnet Fe3GaTe2

TL;DR

This study maps the precise impurity occupancy pathway of Ni in Fe3GaTe2, revealing how Ni atoms occupy specific lattice sites and influence magnetic properties, providing insights for tuning quantum materials.

Contribution

It establishes the impurity occupancy roadmap for Ni in Fe3GaTe2 using combined experimental and theoretical methods, a novel approach for understanding impurity effects in layered ferromagnets.

Findings

Ni initially occupies van der Waals gap sites at low x

Ni gradually replaces Fe2 sites as x increases

Magnetic properties correlate with Ni site occupancy

Abstract

Impurity substitution is a general strategy to study the intrinsic properties of a quantum material. However, when the target element has more than one Wyckoff position in the lattice, it is a big challenge but with extreme necessity to know the exact position and order of the occupancy of impurity atoms. Via comprehensive experimental and theoretical investigations, we establish herein the roadmap for Ni substitution in Fe3GaTe2, a van der Waals ferromagnet with the Curie temperature TC even reaching ~ 380 K. The results unambiguously reveal that in (Fe1-xNix)3GaTe2, Ni atoms initially form an van der Waals interlayer gap Ni3 sites when x < 0.1, and then gradually occupy the Fe2 sites. After replacing the Fe2 sites at x of ~ 0.75, they start to substitute for the Fe1 sites and eventually realize a full occupation at x = 1.0. Accordingly, TC and saturation magnetic moments of (Fe1-xNix)3GaTe2 both show nonlinear decrease, which is tightly tied to the Ni occupancy order as well as the different roles of Ni3, Fe1 and Fe2 sites in the spin Hamiltonian. The results not only yield fruitful insights into the essential roles of different Fe sites in producing the above room temperature high TC, but also set a paradigm for future impurity substitution study on other quantum materials.