The magnetic anomaly and NRM directions of Odessa octahedrite

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The magnetic anomaly of the Odessa octahedrite (3.7 kg, a single crystal) was measured at 1, 5, 10, and 40 cm from the surface using a uniaxial fluxgate magnetometer in a μ-metal magnetic shield environment. The NRM directions of cubic subsamples were measured to take into consideration the role of the octahedron crystallography during AF demagnetization. These results indicated that the observed anomalies are strongly controlled by the shape anisotorpy of the sample rather than the crystallography of the octahedrite, although weak complicated anomalies which may be related to structure appeared above 1 cm from the surface. The natural remanent magnetization of cubic subsamples was controlled by the octahedral γ(111) planes, as demagnetized directions occurred along these planes. Namely, the preferable direction of NRM is the intersection among the great circles of γ(111) crystallographic planes which are consistent with the result obtained by A. Brecher and L. Albright (J. Geomagn. Geoelectr., 29, 379, 1977). The origin of the stable NRM component was investigated using the results of microscopic analysis, thermomagnetic curve and hysteresis parameters. Consequently, we concluded that small amounts of taenite grains and lamellae carry the stable component which is distributed along the octahedral γ(111) planes.
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