Magnetic properties of synthetic P2(1)/c (Mg-Fe)SiO3 clinopyroxenes as observed from their low-temperature Mossbauer spectra and from SQUID magnetization measurements

Magnetic properties of six Ca-free P2(1)/c clinopyroxenes along the clinoen statite-clinoferrosilite join were studied by transmission Fe-57 Mossbauer spectroscopy (0.3-4.2 K) and SQUID magnetization measurements (2-300 K). Th e 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 th is study. The magnetic order-disorder transition temperatures T-N were dete rmined by Mossbauer thermoscanning with zero source velocity. The magnetic Mossbauer spectra were refined using a full hyperfine-interaction Hamiltoni an approach assuming different Fe2+-Mg2+ next-nearest-neighbor configuratio ns 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 differen t D-5 electronic level schemes as earlier determined from the paramagnetic Mossbauer spectra. The magnetic susceptibility measurements indicate a posi tive paramagnetic Curie temperature theta (p) for FeSiO3 (x = 1) above 50 K and a negative thetap for x less than or equal to 0.91 above 200 K. The Ne el temperatures as determined from the susceptibility curves are equal to t hose obtained from the thermoscanning, indicating that spin relaxation effe cts can be ruled out. The macroscopic magnetic results further suggest ferr omagnetic ordering of Fe2+ ions within ribbons consisting of two linear ban ds of M2 sites that enclose chains of M1 sites, and antiferromagnetic coupl ing between neighboring ribbons. Generally spoken the magnetic behavior of Ca-free P2(1)/c clinopyroxenes are similar to that of orthopyroxenes with s imilar (Mg,Fe) compositions.