Professor Stephen Blundell

Abstract:

Polycrystalline samples of Sr3MnRuO7 and Sr2Mn0.5Ru0.5O4 have been synthesized and characterized by neutron diffraction, dc magnetometry, and magnetotransport measurements. They are, respectively, n = 2 and n = 1 members of the Ruddlesden-Popper (RP) An+1BnO3n+1 family; both have tetragonal (I4/mmm) symmetry and a disordered distribution of Ru and Mn over the six-coordinate sites within the perovskite layers of the RP structure. Neither compound shows long-range magnetic order at 2 K, but a spin-glass transition is observed at 16 K (n = 1) or 25 K (n = 2). In the case of the n = 2 compound only, the magnetic transition is accompanied by a reduction in the zero-field electrical conductivity. A maximum magnetoresistance of ∼8% in 14 T is found in both compounds.

Abstract:

The interlayer transfer integrals of various organic superconductors have been deduced using high-magnetic-field techniques. The measurements demonstrate the inappropriateness of criteria used to denote incoherent interlayer transport.

Abstract:

The magneto-optical absorption of the quantum Ising ferrornagnet LiHoF4 has been measured in the frequency range 38 to 140 GHz, the temperature range 0.5 to 20 K and magnetic fields of tip to 15 T. The sample was studied in two orientations, with the external magnetic field aligned perpendicular or parallel to the uniaxial direction, i.e., along the quantum and classical directions. In each case, several families of resonances are observed, including linear EPR branches and a series of non-linear fast moving resonances. We present this data and propose all interpretation for the origin of these resonances.