Effect of aligning field on easy-axis orientation of directly synthesized L10 nanoparticles

In this research, the improved synthesis and alignment of L1₀ FePt nanoparticles and the measured dependence of alignment on the orienting field are investigated. From the in-plane hysteresis loops of the particles after aligning and drying with a 20-kOe field, the normalized remanence values in the parallel and perpendicular in-plane directions are found to be 0.72 and 0.33 respectively. Also from the loops, the coercivities in the parallel and perpendicular directions are 1.48 kOe and 0.87 kOe, respectively. For comparison, a model for the easy-axis alignment is done assuming that the nanoparticles can freely rotate and achieve a Boltzmann orientation distribution during the drying process. Also, the anisotropy energy is assumed to be sufficiently large so that the easy axis and moment of each particle are nearly parallel during the drying process. Using an appropriate distribution of particle sizes, the model gives semiquantitative agreement with the measured field dependence of the orientation.