Observation of 4d ferromagnetism in free-standing Pd fine particles

We report on observation of 4d ferromagnetic ordering in pure Pd fine particles. Results of our dc magnetic measurements as a function of Pd particle size show that the magnetization increases rapidly with decreasing particle size; a sample with 59 Å median radius at 1.8 K under 4 kOe shows a factor of nineteen larger magnetization than that of Pd bulk. We suggest that only the surface monolayers of Pd particles are magnetic. The ferromagnetic moment we deduced based on this assumption is 0.23 ± 0.19_μB per atom which is comparable to the value predicted by the ab initio calculation.