RESUMO
The antiferromagnetic to ferromagnetic phase transition in FeRh can be induced globally by either heating the material above its phase transition temperature or applying a combination of external stimuli (such as mechanical strain, electric/magnetic fields) on the material preheated close to its transition temperature. On the other hand, to locally induce this phase transition is more desirable for applications and requires a confined source of energy such as a focused laser beam. Here we combine laser excitation with X-ray magnetic imaging to determine the effect of laser heating on the local and transient magnetization of FeRh using time-resolved photoelectron emission microscopy. Excitation by an ultrashort laser pulse generates a local ferromagnetic state within 0.6ns which recovers its initial antiferromagnetic state after a further 2ns. The form of the domains during the growth and diminution of ferromagnetic ordering suggests an intrinsic speed limit for magnetic and structural changes.
RESUMO
The development of a useful chemistry for the construction of polyfunctional heterocycles--first through solution and solid phase (resins) and then library production via SynPhase crowns--is reported. Bead-based synthetic work was done on Merrifield resin where treatment with benzylamine in the presence of DBU followed by reaction with 4-chloromethylbenzoyl chloride afforded amide-linked resin 9. Finally, TFA.NH2-polystyrene macro crowns were derivatized with 4-(hydroxymethyl)benzoic acid to afford pin 14 which was coupled with Boc-protected amino acid 2 in the presence of DIC to deliver pin 15. Deprotection and reaction with phenyl isocyanate afforded urea functionalized pin 17 which underwent 1,3-dipolar cycloaddition reaction to give pin 19. Finally, compound 20 was obtained with moderate diastereoselectivity (20:21::8:1) by the reaction of pin 19 with a catalytic amount of Et3N.
