Theoretical treatment of the mixed ferro-ferrimagnets composed of ternary-metal Prussian blue analogs in a paramagnetic region

摘要

Our objective in the series of the present work is to obtain a type of magnet in which the weight average of ferromagnetic and ferrimagnetic characters is precisely controlled by fine tuning of the composition. For this attempt, we have prepared the ((NixMn1-xII)-Mn-II)(1.5)[Cr-III(CN)(6)]. zH(2)O system, incorporating both ferromagnetic Ni-II-Cr-III (J(NiCr)) and antiferromagnetic Mn-II-Cr-III (J(MnCr)) exchange interactions. In this work, its magnetic properties in a paramagnetic region, such as magnetic susceptibility (chi) and Weiss temperature (theta(C)), were studied. In general, the chi(-1) Value for typical ferromagnets and ferromagnets should be zero at Curie temperature (T-C). However, the observed chi(-1) value for x = 0.30 of this system did not drop off at T-C. The theoretical analysis based on a molecular-field theory considering both ferromagnetic (J(NiCr) > 0) and antiferromagnetic (J(MnCr) < 0) exchange interactions showed that this phenomenon occurred because a compensation temperature is close to T-C. In addition, it showed that the variation of the theta(C), value is not due to changes in the magnitudes of superexchange interactions but due to changes in the weighted average of J(NiCr) and J(MnCr) as a function of x. [S0163-1829(99)09941-5]. [References: 33]