Magnetic properties of the clinopyroxenes aegirine and hedenbergite: A magnetic susceptibility study on single crystals

Two natural clinopyroxene single crystals were investigated, an aegirine-augite (AEC) and a magnesian hedenbergite (HED). Both samples were carefully characterized by electron microprobe, X-ray diffraction, and Mossbauer spectroscopy. Magnetic susceptibility measurements of powdered samples reveal low temperature antiferromagnetic coupling and Curie-Weiss behaviour with T-N=7.5(5) K, Theta(p)= -19(1) K for AEG, and T-N= 31 (1) K, Theta(p)= +21 (1) K for HED, respectively. Low temperature Mossbauer spectra exhibit relaxation phenomena. Magnetic susceptibility measurements of the single crystals show the direction of the magnetic moments to be lying within the a/c plane for both samples: 50(+/- 2)degrees from a and 57 (+/- 2)degrees from c in AEG, and 45 (+/- 2)degrees from a and 60 (+/- 2)degrees from c in HED, respectively. The antiferromagnetic interchain interaction competes with the ferromagnetic intrachain interaction in both pyroxenes. In the magnesian hedenbergite a field induced magnetic transition is found. Its dependence on temperature, magnetic field and crystallographic direction is investigated and described.