Spin-polarized photoelectron diffraction of nanoscale manganese structures

Abstract

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 3 s core level 5 S and 7 S multiplets. This occurs at a temperature of 505 ± 20 K or 5.3 times T N , the bulk Néel 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 (∼25%) in the nanoscale system produced an enhanced photoemission signal from the surface allowing a deconvolution of surface and interior contributions to the 3 s spectra. We thus show that the step in the ratio of multiplet intensities arises entirely from the surface component of the 3 s spectrum. This supports a recent interpretation that the step is due to a surface specific transition in longrange magnetic order that can be well above T N,bulk for antiferromagnets and T C,bulk for ferromagnets.