Professor Stephen Blundell

Abstract:

The magnetic ground states of the isostructural double perovskites Ba 2NaOsO6 and Ba2LiOsO6 are investigated with muon-spin relaxation. In Ba2NaOsO6 long-range magnetic order is detected via the onset of a spontaneous muon-spin precession signal below Tc=7.2±0.2K, while in Ba 2LiOsO6 a static but spatially disordered internal field is found below 8 K. A probabilistic argument is used to show from the observed precession frequencies that the magnetic ground state in Ba 2NaOsO6 is most likely to be low-moment (≈0.2μB) ferromagnetism and not canted antiferromagnetism. Ba2LiOsO6 is antiferromagnetic and we find a spin-flop transition at 5.5T. A reduced osmium moment is common to both compounds, probably arising from a combination of spin-orbit coupling and frustration. © 2011 American Physical Society.

Abstract:

We present a muon-spin relaxation study of local magnetism in the molecule-based metamagnet [Ru2(O2CMe)4] 3[Cr(CN)6]. We observe magnetic order with T N=33 K, although above 25 K the sublattice spins become less rigid and a degree of static magnetic disorder is observed. The comparison of measurements in applied magnetic field with simulations allows us to understand the origin of the muon response across the metamagnetic transition and to map out the phase diagram of the material. Applied hydrostatic pressures of up to 6 kbar lead to an increase in the local magnetic field along with a complex change in the internal magnetic-field distribution. © 2011 American Physical Society.