Formation of single-magnetic-domain iron particles via vapor-phase nucleation: Implications for the solar nebula

We report experimental evidence of the production of single-magnetic-domain iron grains via vapor-phase nucleation even in the absence of an ambient m agnetic field. These single domain grains are thermodynamically stable as f ully saturated magnetic dipoles, The spontaneous formation of fully magneti zed single-domain iron grains, and by inference a variety of other single-d omain particles such as taenite or magnetite, could greatly increase the co agulation efficiency of submicrometer-sized grains in the primitive solar n ebula. An important test of this hypothesis is proposed: an examination of 20- to 50-nm diameter iron grains in the matrix of very primitive chondrite s should reveal an interconnected, three-dimensional string or web-like str ucture within the matrix.