PNNL

Abstract

Mn1.68Co0.24Ni0.48Cu0.6O4 was produced by slip casting and sintering of spray-pyrolysis produced powders. Magnetic properties of this composition were measured for the first time, as a function of processing temperature (900 or 1000°C sintering), to study the effects of Cu and Mn valence and site preference. Quantitative x-ray photoelectron spectroscopy showed that Cu+ site occupancy changed from tetrahedral to a mix of tetrahedral and octahedral with increasing sintering temperature. X-ray diffraction demonstrated that the materials had a cubic spinel structure devoid of tetragonal Jahn-Teller distortion. AC magnetic susceptibility indicated ferrimagnetic behavior below ~109 K and spin glass behavior below ~66-74 K depending on measurement frequency. Magnitudes of the AC magnetic susceptibility, DC magnetization, and Curie-Weiss temperature were lower for samples sintered at 1000°C than for those sintered at 900°C. AC susceptibility freezing temperatures were modeled with the Vogel-Fulcher law and showed characteristics intermediate between canonical spin glasses and cluster glasses. For the sample sintered at 1000°C, the activation energy for magnetic relaxation was decreased and the interaction parameter temperature was increased compared to the 900°C sample. These materials show promise for advancing fundamental understanding of consequences of multivalent, mixed site occupancy cations on magnetic properties.