Ferromagnetism in fcc Twinned 2.4 nm Size Pd Nanoparticles

Abstract

The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to 0:02 emu=g seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported.

Magnetic and microstructural analysis of palladium nanoparticles with different capping systems

“…However, the magnetization reached at the high field branch of the loop is far from saturation as it is probably due to the coexistence of blocked ferromagnetic entities with superparamagnetic particles and paramagnetic atoms. 1 The same behavior is found for Pd-NR 4 ͑C12͒ for a temperature range between 100 and 275 K ͑Fig. 5͒, with magnetization and coercivity values similar to those obtained for Pd-NR 4 ͑C4͒.…”

“…Local symmetry changes at twin boundaries, as well as surface anisotropy induced by reduction in coordination number were proposed as factors that could contribute to this magnetic behavior. 1 On the other hand, we have also reported permanent magnetism, in small thiol capped gold 8 clusters that cannot be explained by the above-mentioned criterion. In such a system, the large amount of sulfur atoms covalently bonded to the metal cluster, tend to induce "d hole localization" in the metal core, due to charge transfer processes.…”

“…In particular, the study of magnetism in clusters of palladium and in general 4d elements has attracted special attention as these elements are nonmagnetic in bulk. 1,2 Bulk palladium ͑fcc structure͒ presents a high paramagnetic susceptibility value, and it is close to fulfilling the Stoner criterion of magnetism, N͑E F ͒I Ͼ 1, where N͑E F ͒ is the density of states just below the Fermi level ͑E F ͒, and I stands for the Stoner parameter ͑typically 0.71 eV for Pd͒. 3 Accordingly, the factors that can affect the onset of ferromagnetism in Pd are those increasing N͑E F ͒ in order to accomplish the Stoner criterion.…”

Permanent Magnetism, Magnetic Anisotropy, and Hysteresis of Thiol-Capped Gold Nanoparticles

“…An induced magnetic moment has been recently reported for gold at Au-Co interfaces [9], while in Ref. [10] (and references therein) the onset of ferromagnetism in Pd nanoparticles is discussed.…”

Giant magnetic anisotropy at the nanoscale: Overcoming the superparamagnetic limit

“…For 1.4 nm thiol capped gold nanoparticles ͑NPs͒ a permanent magnetism was detected up to room temperature 2,3 whereas a similar behavior had been previously reported for 2.4 nm palladium NPs. 4,5 For the case of gold the appearance of magnetism was completely amazing provided the diamagnetic character of bulk samples and the low value of its density of states at the Fermi level. However, more unexpected was that NPs with sizes smaller than 2.4 nm could exhibit blocked magnetism at 300 K. [2][3][4][5] Moreover, the thermal dependence of magnetization for Pd and Au NPs is very weak between 5 and 300 K. By assuming a first order kinetics for the relaxation of the magnetic moments and an attempted frequency factor equal to approximately 10 10 s −1 , the anisotropy constant for a particle 2 nm size with blocking temperature above 300 K should be at least of10 9 J m −3 that corresponds to approximately 0.4 eV per atom.…”