Zero-temperature transition between antiferromagnetic and ferromagnetic states driven by varying chemical composition in hydrogenated U-2(Ni1-xFex)(2)Sn
Abstrakt
The experiment shows that hydrogenated U-2(Ni1-xFex)(2)Sn is antiferromagnetic for x = 0. With increasing Fe content, the Neel temperature decreases and tends to 0 K at x similar to 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 U2Ni2Sn and Pauli paramagnet U2Fe2Sn 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 DFT-PU calculations. It begins with the calculation of U2Ni2Sn and U2Fe2Sn in their experimental lattices.
Next, we show that for the lattice parameters of U2Ni2Sn, U2Fe2Sn 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. U2Ni2Sn has well-defined U atomic moments and can be mapped on the Heisenberg-type Hamiltonian of interacting U moments.
In U2Fe2Sn, 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 U2Fe2Sn, 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 U-2 (Ni1-xFex)(2)Sn.