Structural and Magnetic Studies of O-Type Ruthenium and Osmium Oxides.

Oxides of the form O with = K, Rb, Cs and = Ru and Os have been synthesized and characterized by diffraction and magnetic techniques. For = K the oxides adopted the tetragonal (4/) scheelite structure. RbOsO, which crystallizes as a scheelite at room temperature, underwent a continuous phase transition to 4/ near 550 K. RbRuO and CsOsO were found to crystallize in the orthorhombic () pseudoscheelite structure, and both displayed discontinuous phase transitions to 4/ at high temperatures. CsOsO was determined to undergo a phase transition to a 2/ structure below 140 K. CsRuO crystallizes with a baryte-type structure at room temperature. Upon heating CsRuO a first order phase transition to the scheelite structure in 4/ is observed at 400 K. A continuous phase transition is observed to 222 below 140 K. DC magnetic susceptibility data is consistent with long-range antiferromagnetic ordering at low temperatures for all compounds except for CsOsO, which is paramagnetic to 2 K. The effective magnetic moments are in agreement with the spin only values for an = 1/2 quantum magnet. Effective magnetic moments calculated for Os compounds were lower than their Ru counterparts, reflective of an enhanced spin orbit coupling effect. A magnetic structure is proposed for RbRuO consisting of predominately antiferromagnetic (AFM) ordering along the 001 direction, with canting of spins in the 100 plane. A small ordered magnetic moment of 0.77 μ was determined.