ABSTRACT
The unusual anisotropy of the spin glass (SG) transition in the pseudobrookite system Fe2TiO5has been interpreted as arising from an induced, van der Waals-like, interaction among magnetic clusters. Here we present susceptibility (χ) and specific heat data (C) for Fe2TiO5diluted with non-magnetic Ga, (Fe1-pGap)2TiO5, for disorder parameterp= 0, 0.11, and 0.42, and elastic neutron scattering data forp= 0.20. A uniform suppression ofTgis observed upon increasingp, along with a value ofχTgthat increases asTgdecreases, i.e.dχ(Tg)/dTg<0We also observeCTâT2in the low temperature limit. The observed behavior places (Fe1-pGap)2TiO5in the category of a strongly geometrically frustrated SG.
ABSTRACT
The recent reports of superconductivity in Nd1-x Sr x NiO2/SrTiO3 heterostructures have reinvigorated interest in potential superconductivity of low-oxidation state nickelates. Synthesis of Ni1+-containing compounds is notoriously difficult. In the current work, a combined sol-gel combustion and high-pressure annealing technique was employed to prepare polycrystalline perovskite Nd1-x Sr x NiO3 (x = 0, 0.1, and 0.2). Metal nitrates and metal acetates were used as starting materials, and the latter were found to be superior to the former in terms of safety and reactivity. The Nd1-x Sr x NiO3 compounds were subsequently reduced to Nd1-x Sr x NiO2 using calcium hydride in a sealed, evacuated quartz tube. To understand the synthesis pathway, the evolution from NdNiO3 to NdNiO2 was monitored using in situ synchrotron x-ray diffraction during the reduction process. Electrical transport properties were consistent with an insulator-metal transition occurring between x = 0 and 0.1 for Nd1-x Sr x NiO3. Superconductivity was not observed in our bulk samples of Nd1-x Sr x NiO2. Neutron diffraction experiments at 3 and 300 K were performed on Nd0.9Sr0.1NiO2, in which no magnetic Bragg reflections were observed, and the results of structural Rietveld refinement are provided.
