The experiment shows that hydrogenated ${\mathrm{U}}_2{\left({\mathrm{Ni}}_{1-x}{\mathrm{Fe}}_x\right)}_2\mathrm{Sn}$ is antiferromagnetic for $x=0$. With increasing Fe content, the Néel temperature decreases and tends to 0 K at $x\sim 20\%$. Further increase of $x$ results in the ferromagnetism of the system. This paper suggests an explanation why the material that, from its chemical composition, is intermediate between antiferromagnet ${\mathrm{U}}_2{\mathrm{Ni}}_2\mathrm{Sn}$ and Pauli paramagnet ${\mathrm{U}}_2{\mathrm{Fe}}_2\mathrm{Sn}$ turns in the hydrogenated form to the ferromagnetic state—a state that is very unusual for the U compounds with the given crystal lattice. Our theoretical study is based on density functional theory (DFT) and $\mathrm{DFT}+U$ calculations. It begins with the calculation of ${\mathrm{U}}_2{\mathrm{Ni}}_2\mathrm{Sn}$ and ${\mathrm{U}}_2{\mathrm{Fe}}_2\mathrm{Sn}$ in their experimental lattices. Next, we show that for the lattice parameters of ${\mathrm{U}}_2{\mathrm{Ni}}_2\mathrm{Sn}, {\mathrm{U}}_2{\mathrm{Fe}}_2\mathrm{Sn}$ becomes magnetic. To understand deeper the dependence of the magnetic states on the lattice parameters, we model quantum phase transitions in both parent systems. We find that a drastic difference of the $3d-5f$ hybridization in the two systems leads to fundamentally different types of the magnetic states. ${\mathrm{U}}_2{\mathrm{Ni}}_2\mathrm{Sn}$ has well-defined U atomic moments and can be mapped on the Heisenberg-type Hamiltonian of interacting U moments. In ${\mathrm{U}}_2{\mathrm{Fe}}_2\mathrm{Sn}$, strong $5f-3d$ hybridization leads to both the Pauli paramagnetism for the equilibrium lattice and the simultaneous appearance of comparable in value U and Fe spin moments for larger lattice parameters. The presence of the Fe moments is shown to be essential for the magnetism of ${\mathrm{U}}_2{\mathrm{Fe}}_2\mathrm{Sn}$, which imposes strong constraint on the magnetic structure of the U sublattice requesting it to be ferromagnetic. The established correlation between U and Fe spin moments is crucial for the explanation of the ferromagnetism of the hydrogenated ${\mathrm{U}}_2{\left({\mathrm{Ni}}_{1-x}{\mathrm{Fe}}_x\right)}_2\mathrm{Sn}$.

• Received 7 December 2021
• Revised 31 March 2022
• Accepted 1 April 2022

DOI:https://doi.org/10.1103/PhysRevB.105.134411