Magnetization of Pt13 clusters supported in a NaY zeolite: A XANES and XMCD study

X-ray absorption and x-ray magnetic circular dichroism (XMCD) spectra have been recorded at the Pt L-2,L-3 edges of Pt-13 and hydrogenated Pt13Hm clusters dispersed in NaY zeolite. A Pt foil was also measured as reference for comparison with bulk Pt. From the x-ray absorption near edge structure measurements the average number of holes n(h) in the 5d band of these systems is found. In the Pt13Hm sample the Pt-H antibonding state increases n(h) with respect to the Pt-13 sample. It gives rise to a shape resonance with energy E-res=2.3 eV. The average orbital and spin moments m(L) and m(S) for the Pt atom have been determined from the XMCD measurements. The total magnetic-moment field dependence XMCD(H) was determined and scaled to the absolute value of the average moment per Pt atom. The fit of XMCD(H) to a Langevin function yields a magnetic moment per cluster of mu=3.7 +/- 0.4 and 3.0 +/- 0.4 mu(B), for Pt-13 and Pt13Hm, respectively. It is shown that nonmagnetic clusters coexist with those giving magnetic signal. The amount of Pt constituting the magnetic Pt-13 clusters is 15-20% of the total Pt content. The XMCD data are compared with superconducting quantum interference device magnetization measurements. The moment found indicates that the cluster spin of Pt-13 and Pt13Hm is in the range S approximate to 2-3. They are compared to predictions calculated by density-functional methods.