We investigate ferromagnetism of two-dimensional Pd nanoparticle superlattice by a magnetoresistance measurement. Magnetoresistance increases at a coercive field with hysteretic behavior, which is consistent with the result of a magnetization-field curve. This indicates that the ferromagnetism of the Pd nanoparticle superlattice is electrically detected. From the maximum magnetoresistance change, the conduction-electron polarization of the Pd nanoparticle superlattice is estimated to be ∼4%. The ferromagnetism of Pd nanoparticles is evolved ferromagnetism without protective agents; therefore, the origin of ferromagnetism in the chemically prepared Pd nanoparticles is associated with the intrinsic characteristic of the Pd nanoparticles, but not the effect of the existence of a protective agent.
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