Three-dimensional antiferromagnetism in triamminodiperoxychromate, Cr(NH3)3(O2)2: a precursor to a new class of Cr(IV) magnets

This study presents the first observation of long-range antiferromagnetic order in a simple Cr(IV)-peroxo, S=1 complex. Magnetic susceptibility, χ, and heat capacity, Cp, results are presented for both powders and single crystals of triamminodiperoxychromate, Cr(NH3)3(O2)2. For the investigated compound, the spin state of S=1 was determined by analysis of χ from 2 to 200 K, and correlated with the entropy expected for such a system as determined by Cp measurements from 2.5 to 20 K. Sharp λ-like transitions were observed in both χ and Cp, with maxima at 8.80 and 8.46 K, respectively; characteristic of three-dimensional long-range antiferromagnetic ordering. The χ and Cp results correlated well using the Fisher heat capacity relationship. Further analysis of Cp determined that the majority of the spin entropy is engaged at temperatures below 8.46 K. This class of compounds might serve as precursors for CrO2 related materials.