Magnetic ground state of the ordered double-perovskite Sr2YbRuO6 : Two magnetic transitions

Abstract

Comprehensive muon-spin-rotation/relaxation (μSR) and neutron powder-diffraction (NPD) studies supported via bulk measurements have been performed on the ordered double-perovskite Sr 2 YbRu O 6 to investigate the nature of the magnetic ground state. Two sharp transitions at T N 1 ∼ 42 K and T N 2 ∼ 36 K have been observed in the static and dynamic magnetization measurements, coinciding with the heat-capacity data. In order to confirm the origin of the observed phase transitions and the magnetic ground state, microscopic evidences are presented here. An initial indication of long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate near T N 1 . NPD confirms that the magnetic ground state of Sr 2 YbRu O 6 consists of an antiferromagnetic (AFM) structure with interpenetrating lattices of parallel Y b 3 + and R u 5 + moments lying in the a b plane and adopting an A-type AFM structure. Intriguingly, a small but remarkable change is observed in the long-range ordering parameters at T N 2 confirming the presence of a weak spin reorientation (i.e., change in spin configuration) transition of Ru and Yb moments, as well as a change in the magnetic moment evolution of the Y b 3 + spins at T N 2 . The temperature-dependent behavior of the Y b 3 + and R u 5 + moments suggests that the 4 d electrons of R u 5 + play a dominating role in stabilizing the long-range-ordered magnetic ground state in the double-perovskite Sr 2 YbRu O 6 whereas only the Y b 3 + moments show an arrest at T N 2 . The observed magnetic structure and the presence of a ferromagnetic interaction between Ru and Yb ions are explained with use of the Goodenough-Kanamori-Anderson rules. Possible reasons for the presence of the second magnetic phase transition and of a compensation point in the magnetization data are linked to competing mechanisms of magnetic anisotropy.