Stabilisation of magnetic ordering in La3Ni2-xCuxB’O9 (B’ = Sb, Ta, Nb) by the introduction of Cu2+

Abstract La 3 Ni 2- x Cu x B ’O 9 ( x  = 0.25; B ’ = Sb, Ta, Nb: x  = 0.5; B ’ = Nb) have been synthesized and characterised by transmission electron microscopy, neutron diffraction and magnetometry. Each adopts a perovskite-like structure (space group P 2 1 / n ) with two crystallographically-distinct six-coordinate sites, one occupied by a disordered arrangement of Ni 2+ and Cu 2+ and the other by a disordered ∼1:2 distribution of Ni 2+ and B ′ 5+ , although some Cu 2+ is found on the latter site when x  = 0.5. Each composition undergoes a magnetic transition in the range 90 ≤  T /K ≤ 130 and shows a spontaneous magnetisation at 5 K; the transition temperature always exceeds that of the x  = 0 composition by ≥ 30 K. A long-range ordered G-type ferrimagnetic structure is present in each composition, but small relaxor domains are also present. This contrasts with the pure relaxor and spin-glass behaviour of x  = 0, B ’ = Ta, Nb, respectively.