Three-dimensional antiferromagnetism in triamminodiperoxychromate, Cr(NH3)(3)(O-2)(2): a precursor to a new class of Cr(IV) magnets

This study presents the first observation of long-range antiferromagnetic o rder in a simple Cr(IV)-peroxo, S = 1 complex. Magnetic susceptibility, chi , and heat capacity, C-p, results are presented for both powders and single crystals of triamminodiperoxychromate, Cr(NH3)(3)(O-2)(2). For the investi gated compound, the spin state of S = 1 was determined by analysis of chi f rom 2 to 200 K, and correlated with the entropy expected for such a system as determined by C-p measurements from 2.5 to 20 K. Sharp lambda -like tran sitions were observed in both chi and C-p, with maxima at 8.80 and 8.46 K, respectively; characteristic of three-dimensional long-range antiferromagne tic ordering. The chi and C-p results correlated well using the Fisher heat capacity relationship. Further analysis of C-p determined that the majorit y of the spin entropy is engaged at temperatures below 8.46 K. This class o f compounds might serve as precursors for CrO2 related materials. (C) 2001 Elsevier Science Ltd. All rights reserved.