Crystal structures and magnetic properties of rare earth tantalates RE 3TaO7 (Re = rare earths)

Abstract

The crystal structures and magnetic properties of rare earth tantalates RE3aO7 (RE = rare earths) are reported. Their crystal structures were grouped into three types: La3NbO7-type, Y3TaO7-type, and defect-fluorite-type. For the Ho 3TaO7y compound, two different phases (Y 3sTaOy-type and defect-fluorite-type) were prepared. At around room temperature, Nd3TaO7 was found to transform from the Y3TaO7-type phase to LaaNbOv-type phase with increasing temperature. Temperature dependences of the magnetic susceptibilities and specific heats indicated that the Nd and Tb compounds undergo a 'two-step' antiferromagnetic transition with separate ordering of ions on different crystallographic sites below 2.6 and 3.6 K, respectively. The Dy3+ ion was found to be in an antiferromagnetic state below 2.3 K. The Ho 3TaO7 with the Y3TaO7-type structure showed an antiferromagnetic-like transition, while no magnetic ordering was observed down to 1.8 K for the defect-fluorite-type Ho3TaO 7.