MAGNETIC-PROPERTIES OF THE CLINOPYROXENES AEGIRINE AND HEDENBERGITE -A MAGNETIC-SUSCEPTIBILITY STUDY ON SINGLE-CRYSTALS

Two natural clinopyroxene single crystals were investigated, an aegiri ne-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 powde red samples reveal low temperature antiferromagnetic coupling and Curi e-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 temperatu re Mossbauer spectra exhibit relaxation phenomena. Magnetic susceptibi lity measurements of the single crystals show the direction of the mag netic 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 ferromagnet ic intrachain interaction in both pyroxenes. In the magnesian hedenber gite a field induced magnetic transition is found. Its dependence on t emperature, magnetic field and crystallographic direction is investiga ted and described.