Topochemical nitridation of Sr2FeMoO6

Roberta Ceravola, Carlos Frontera, Judith Oro ́-Solé, Ashley P. Black, Clemens Ritter,  Ignasi Mata, Elies Molins, Josep Fontcuberta* and  Amparo Fuertes

Chem.Commun. 55, 3105 (2019)

DOI: 10.1039/c8cc09845j

ABSTRACT

The topotactic nitridation of cation ordered, tetragonal Sr₂FeMoO₆ in NH₃ at moderate temperatures leads to cubic, Fmm double perovskite oxynitride Sr₂FeMoO_4.9N_1.1 where double-exchange interactions determine ferromagnetic order with T_C ≈ 100 K. Substitution of oxide by nitride induces bond asymmetries and local electronically driven structural distortions, which combined with Fermi level lowering restricts charge itinerancy to confined regions and preclude spontaneous long-range magnetic order. Under a magnetic field, ferromagnetic correlations expand, favoring charge delocalization and a negative magnetoresistance is observed.