Effects of ion-beam irradiation on the L1\u3csub\u3e0\u3c/sub\u3e phase transformation and their magnetic properties of FePt and PtMn films (Invited)

In this paper, we illustrate how to modify the structure and magnetic properties of L10 FePt and PtMn films using ion-beam irradiation. Highly ordered L10 FePt and PtMn phases were achieved directly by using 2 MeV He-ion irradiation without conventional post-annealing. A high ion-beam current density (~μA/cm2 ) was used to achieve direct beam heating on samples. This irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered L10 phase. In-plane coercivity of FePt films greater than 5700 Oe could be obtained after disordered FePt films were irradiated with a He-ion dose of 2.4x1016 ions/cm2. The direct ordering of FePt took place by using ion-irradiation heating at a temperature as low as 230 ℃. In PtMn-based spin valves, an L10 PtMn phase, a large exchange field and a high giant magnetoresistance (GMR) ratio (11%) were simultaneously obtained by using He-ion irradiation. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and the GMR of PtMn-based spin valves, respectively

Synthesis and characterization of comb-shaped polyesters based on 2-octadecyl-1,3-propanediol and phthalic acids

Three isomeric poly(2-octadecyl-1,3-trimethylene phthalate)s were prepared by melt transesterification of the corresponding diphenyl ester and 2-octadecyl-1,3-propanediol. Intrinsic viscosity, size exclusion chromatography and light scattering determinations yielded weight-average molecular masses of 110 000 and higher. High-resolution, solution C-13 n.m.r. spectroscopy analysis of both the diphenyl ester precursors and polyesters identified the main-chain units, the isomeric aromatic acid residue and glycol carbons, the linking and the terminal ends of the octadecyl side chain, and finally allowed detection of phenyl ester end groups at 1-2% level. No absorption band due to hydroxyl end groups was monitored in the i.r. polyester spectra. I.r. spectroscopy, d.s.c. and powder X-ray diffractometry provided a clear indication of the crystallinity of the prepared polyesters. The relevant melting enthalpy values and X-ray diffraction patterns were typical of comb-shaped polymers in which the paraffinic side chains crystallize independently with their characteristic hexagonal packing