New low-temperature ferrimagnets

The ferrimagnetic properties of three new Cr(III)/Fe(III) bimetallic salts, namely [Cr(NH3)5(H2O)][FeCl6], [Cr(NH3)4(H2O)2][FeCl6] and [Cr(en)3]3[FeCl6]Cl6.H2O, are reported. The respective ordering temperatures are Tc = 2.32, 2.31 and 0.91 K. The ac susceptibility data on the three compounds at temperatures above Tc can be fit to a Néel hyperbola.The research in Zaragoza and Barcelona has been supported respectively by Grants 3380/83 and 409/84, from the Comision Asesora de Investigacion Cientifica y Tecnica of the Ministerio de Educacion y Ciencia. The research in Chicago has been supported by Grant DMR-85 15224 fromthe SolidState Chemistry Program, Division of Materials Research of the National Science Foundation. Cooperative work has been supported by Grant CCB-8504/001 from the American—Spain Joint Committee for Technical and Scientific Cooperation. One of us (MCM) wants also to acknowledge a postgraduate student fellowship fromthe Ministerio de Educacion y Ciencia.Peer Reviewe