Spin-polarized photoelectron diffraction of nanoscale manganese structures

Magnetic ordering in bulk Mn and nanoscale Mn islands deposited on highly oriented pyrolytic graphite has been investigated with spin-polarised photoelectron diffraction (SPPED). Results for the bulk film show the expected step in the ratio of intensities of the Mn 3s core level S-5 and S-7 multiplets. This occurs at a temperature of 505 +/- 20 K or 5.3 times T-N, the bulk Neel temperature and compares well with similar data from Mn compounds. In contrast the equivalent step observed with mesoscopic Mn islands of mean size 6 nm is found to occur at 85 +/- 15 K, that is, at about T-N. The high proportion of surface atoms (similar to 25%) in the nanoscale system produced an enhanced photoemission signal from the surface allowing a deconvolution of surface and interior contributions to the 3s spectra. We thus show that the step in the ratio of multiplet intensities arises entirely from the surface component of the 3s spectrum. This supports a recent interpretation that the step is due to a surface specific transition in long-range magnetic order that can be well above T-N,T-bulk for antiferromagnets and T-C,T-bulk for ferromagnets. (C) 1998 Elsevier Science Ltd. All rights reserved.