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The spin pinning in the oxide surface layer has been observed directly, and it is considered a possible reason why the oxide layer leads to the decrease of the specific saturation magnetization for fine iron particles. The pinning depth has been estimated by means of a Mössbauer effect under an applied field of 6 T in a thermal-cycle process. The Debye temperature of the oxide layer and the temperature dependence of f2/f1 have been obtained, where f1 and f2 are the Mössbauer recoilless fractions for the inner α-Fe core and the oxide layer, respectively. Furthermore, the estimation for the thickness of an oxide layer has been improved.

Magnetite chains of spheres with different radii and lengths were prepared by aging ferrous hydroxide gel with 0.2M KNO3 under different external magnetic fields which induced the ultra-fine magnetite particles to combine into chain structure. The magnetite particle size and the chain length could be adjusted by varying the field intensity. The chains could be deposited on silicon substrates to form aligned structure in magnetic field. The hysteresis loops were measured in different directions by a vibrating sample magnetometer (VSM). The structure and magnetic properties were discussed.

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