Crystal structure and electronic properties of Ca4Mn2TiO9.93, an n=3 Ruddlesden-Popper compound
J MATER CHEM 11:1 (2001) 160-167
Abstract:
Traditional solid state synthetic methods were used to prepare a polycrystalline sample of the n = 3 Ruddlesden-Popper phase Ca4Mn2TiO9.93. The crystal structure (space group Pbca, a = 5.31411(5), b = 5.31148(5), c = 26.9138(2)Angstrom) was determined by the simultaneous analysis of neutron and X-ray diffraction data, with near-edge anomalous scattering being used to provide contrast between Mn and Ti cations. The latter show a small preference for the octahedral sites at the centre of the three-layer perovskite blocks within the structure. Neutron diffraction data collected at 5 K show no evidence for long-range magnetic ordering, although an enhanced magnetisation with a weak remanence is observed at low temperature; this is ascribed to the presence of antisymmetric exchange interactions. Ca4Mn2TiO9.93 is a semiconductor with a temperature-dependent activation energy of similar to 100 meV. Only weak (rho (B)/rho (0) > 0.9 in 14 T at 75 K) magnetoresistance was observed.Fermi surface shape and angle-dependent magnetoresistance oscillations
JOURNAL OF PHYSICS-CONDENSED MATTER 13:10 (2001) 2271-2279
Organic magnetic materials studied by positive muons
HYPERFINE INTERACT 133:1-4 (2001) 169-177
Abstract:
Positive muons can be implanted into organic and molecular magnets in order to study their internal magnetic field distribution and any associated dynamics. The muon behaves essentially as a "microscopic magnetometer", sensitive to local magnetic order and magnetic fluctuations. We describe some recent experiments using this technique which were performed on a variety of organic systems, including nitronyl nitroxide magnets and materials with spin-Peierls ground states, MF-M(TCNQ)(2) and DEM(TCNQ)(2), and demonstrate how the technique can give information concerning their ground states.Enhancement of the magnetoresistance at the curie temperature of the ferromagnetic insulator La1.5 Sr0.5 MnRhO6
Physical Review B - Condensed Matter and Materials Physics 62:10 (2000) R6077-R6080
Abstract:
We report a study of the magnetic and electrical properties of the ferromagnetic insulator La1.5Sr0.5MnRhO6. A significant magnetoresistance is found in this system which is largest at the Curie temperature (Tc) even though there is no metal-insulator transition. The electrical transport is found to be activated above Tc and described by a variable range hopping law below Tc. Above Tc the carriers are magnetic polarons with a size which increases as the temperature approaches the magnetic transition. Rh substitution preserves ferromagnetic ordering, in contrast with the effect of other dopants on the B sites, but modifies the electrostatic potential leading to carrier localization. We attribute the peak in the magnetoresistance at Tc to the field-induced suppression of critical spin fluctuations which modulate the energetic barriers seen by the carriers.A mu SR study of high oxidation state iron oxides displaying large magnetoresistance
PHYSICA B 289 (2000) 89-93