Abstract

Magnetic properties of six Ca-free P21/c clinopyroxenes along the clinoenstatite-clinoferrosilite join were studied by transmission 57Fe Mössbauer spectroscopy (0.3–4.2 K) and SQUID magnetization measurements (2–300 K). The FexMg1−xSiO3 members were synthesized in a multi-anvil press, and samples with x = 1.00, 0.91, 0.87, 0.78, 0.61, and 0.09 have been considered in this study. The magnetic order-disorder transition temperatures TN were determined by Mössbauer thermoscanning with zero source velocity. The magnetic Mössbauer spectra were refined using a full hyperfine-interaction Hamiltonian approach assuming different Fe2+-Mg2+ next-nearest-neighbor configurations of the probe nuclei to give a distinct spectral component. The different strengths of the M1 and M2 hyperfine fields can be related to the different 5D electronic level schemes as earlier determined from the paramagnetic Mössbauer spectra. The magnetic susceptibility measurements indicate a positive paramagnetic Curie temperature 𝛉P for FeSiO3 (x = 1) above 50 K and a negative 𝛉P for x ≤ 0.91 above 200 K. The Néel temperatures as determined from the susceptibility curves are equal to those obtained from the thermoscanning, indicating that spin relaxation effects can be ruled out. The macroscopic magnetic results further suggest ferromagnetic ordering of Fe2+ ions within ribbons consisting of two linear bands of M2 sites that enclose chains of M1 sites, and antiferromagnetic coupling between neighboring ribbons. Generally spoken the magnetic behavior of Ca-free P21/c clinopyroxenes are similar to that of orthopyroxenes with similar (Mg,Fe) compositions.

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