Substitution effects and magnetic order in the sulfide spinels MnLu2S4 and MnLu1.8Me0.2S4 (Me = Ho, Er and Cr)

Abstract

The synthesis, crystallochemical and magnetic properties of sulfide spinels based on manganese and lutetium are reported. The stoichiometric non-substituted compound MnLu₂S₄ is a normal spinel, with manganese at the tetrahedral sites and lutetium at the octahedral sites. The experimental magnetic moment indicates a 2+ oxidation state for Mn. Partial substitution of lutetium by Er and Ho slightly weakens the antiferromagnetic character of the Weiss parameter (Θ = −15 K for MnLu₂S₄) due to a larger separation of the Mn²⁺ ions, but it does not create any magnetic interaction, neither between the RE ions nor between the manganese spins. Inversely, 10% substitution of lutetium by chromium Cr³⁺ (MnLu_1.8Cr_0.2S₄) triggers long-range ferromagnetic interactions below T_c = 67 K, although antiferromagnetic components still predominate. The ordered state, ferrimagnetic or AF-canted type, is studied by ZFC/FC cycles under different fields and temperatures.