Magnetism in the complex cobaltates Y1−xSrxCoO3−δ (0.7 ≤ x ≤ 0.95) and Ca3Co2O6

The magnetic phases in the complex cobaltates Y1−xSrxCoO3−δ (0.7 ≤ x ≤ 0.95) and Ca3Co2O6 have been investigated by susceptibility, heat capacity, X-ray and neutron scattering techniques. These measurements have shown that the super- structure ordering in the perovskite cobaltate Y1−xSrxCoO3−δ which evolves as a function of temperature heavily influences the ferrimagnetic behaviour of this mate- rial. Neutron scattering has also been used to probe the unusual time and magnetic field dependent behaviour of the spin-chain compound Ca3Co2O6, and to further our understanding of the magnetic phase diagram of this system. Both polycrystalline and single crystal samples have been used in this study. High quality single crystals of the A-site (Sr/Y) and oxygen vacancy ordered form of the perovskite Y1−xSrxCoO3−δ have been produced using the floating zone technique and characterised using EDAX and TGA. The single crystals produced were large enough to perform polarised and inelastic neutron scattering experiments on this compound for the first time, revealing anisotropic quasi-elastic scattering above the magnetic transition temperature. In addition, diffraction experiments on these samples found evidence of coincident structural and magnetic transitions in Y1−xSrxCoO3−δ at both 370 and 280 K. Neutron diffraction measurements were also performed on the geometrically frustrated compound Ca3Co2O6. The low temperature magnetisation process was found to be accompanied by clearly visible steps in the intensity of the ferromagnetic and antiferromagnetic Bragg peaks. Detailed measurements have shown that the presence of short-range correlations cannot account for the reduction in intensity of the antiferromagnetic Bragg peaks at low temperatures. Instead, the origin of this drop in intensity was found to be a slow time-dependent magnetic transition from one long-range ordered antiferromagnetic state to another. This transition occurs over a timescale of hours and is never complete. The experimental work detailed in this thesis provides new information about the phase diagrams of Y1−xSrxCoO3−δ and Ca3Co2O6 and contributes to our overall understanding of the physics of these complex cobaltate compounds

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

On the growth and properties of high quality single crystals of the yttrium doped strontium cobaltates, Y1−xSrxCoO3−δ (0.7 ≤x≤ 0.95)

High quality single-crystals of the A-site and oxygen vacancy ordered variant of yttrium-doped strontium cobaltates Y(1-x)Sr(x)CoO(3-delta) (0.7 <= x <= 0.95) have been produced via the floating zone technique. These materials have been the subject of recent research because of their potential applications in solid state devices and for the unusual sensitivity of their magnetic and transport properties to oxygen content. Initial characterisation measurements show the magnetic susceptibility is nearly isotropic and indicative of a weak ferromagnetic response. The large single crystals we have produced are ideal for experiments with the microscopic probes necessary to understand the true nature of the structural and magnetic properties of these compounds