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Free keywords:
spinels; magnetic ordering; superexchange
Abstract:
We will present here results on the magnetic properties of two
compounds, GeCo2O4 and GeNi2O4, obtained by magnetic susceptibility and
high magnetic field magnetization measurements. GeCo2O4 shows an
antiferromagnetic behaviour with an ordering temperature T-N = 23 K and
a Curie-Weiss temperature theta = +81 K. There is no apparent magnetic
frustration. From the value of the Curie constant, we deduce that Co2+
ions are in high spin S = 3/2 state and that they are bounded in pairs.
We will discuss the possible origin of these pairs. In GeNi2O4, we
observe a negative Curie-Weiss temperature (theta = -15 K). In this
compound the ferromagnetic Ni-Ni direct interaction present in GeCo2O4
cannot exist. Moreover, the nickel cations are not bounded in pairs as
in the cobalt compound. We show that GeNi2O4 is a good candidate for
magnetic frustration. (C) 2003 Elsevier B.V. All rights reserved.
