Structural and Magnetic Properties of the B -Site-Ordered Double Perovskites Ln 2NiTiO6 ( Ln = La, Pr, and Nd)

Structural and magnetic properties of B-site-ordered double perovskites Ln2NiTiO6 (Ln = La, Pr, and Nd) were investigated. The charge formulas were revealed to be Ln23+Ni2+Ti4+O6, which gave a geometrically frustrated face-centered cubic lattice consisting of magnetic Ni2+ (S = 1) cations. In spite of the geometrical spin frustration of Ni2+ spins, the samples show an antiferromagnetic-like magnetic transition at temperatures TN close to their absolute values of the Weiss temperature θ, giving small frustration indices f = |θ|/TN ∼ 1. The small f values are considered to be due to some amount of anti-site disorder between Ni2+ and Ti4+ originating in the small valence difference. The suppression of magnetic ordering in the geometrically frustrated system is strongly affected by the B-site cation ordering in the double perovskites.