Spin-dependent electron dynamics in front of a ferromagnetic surface

Exchange splitting and dynamics of image-potential states in front of a 3 monolayer iron film on Cu(100) have been studied with time-, energy-, and spin-resolved bichromatic two-photon photoemission. For the first image-potential state n=1 we observe an exchange splitting of 56 +/- 10 meV and spin-dependent lifetimes of 16 +/- 2 fs for majority-spin and of 11 +/- 2 fs for minority-spin electrons, respectively. The time-resolved studies of both the population and the linewidth of image-potential states manifest that at the magnetic surface not only inelastic but also quasielastic scattering processes are spin dependent.     

Probing depth of the low energy cascade electrons from a transition metal

A surface probing depth of only 2 layers for low energy cascade electrons excited with a 3.2 keV primary electron beam is clearly demonstrated by model experiments with non-magnetic overlayers of Ta on magnetic substrates of Fe/Ni₈₀Fe₂₀. This result establishes a short probing depth of low energy electrons in transition metals generalizing the previously observed short magnetic probing depth for spin-polarized electrons in ferromagnets. The short probing depth sheds new light on a number of spectroscopic observations on ferromagnetic transition metals, and has important implications concerning surface magnetic properties and scattering processes of hot electrons in transition metals.     

The μSR facilities at PSI

TheSR Facility Instruments presently available at PSI and the envisaged medium- and long-term developments are presented. The plans focus on further upgrades of the existing instruments and the development of new techniques using the very high fluxes becoming available at PSI, in particular the setup of a beamline with a fast kicker for muons on request (MORE) and the development of very low energy muon beams.     

Spin-resolved inverse photoemission of ferromagnetic surfaces

Inverse photoemission (IPE) with spin-polarized electrons provides a way to measure separately the exchange-split majority and minority bands in ferromagnets above the Fermi level. Consequently spin-resolved IPE turns out to be an outstanding technique for obtaining information on surface magnetism: the magnetization of the topmost atomic layer may be investigated by measuring the exchange splitting of electronic states that are localized within the surface layer. Theoretical models of ferromagnetism may be tested by observing the temperature behavior of bands which contribute to the ferromagnetism of the material. The magnetic coupling of an adsorbate to the ferromagnetic substrate may be studied by probing adsorbate-induced bands. Results for the Ni(110) surface serve as an illustration to discuss the status of spin-resolved IPE and its application to the field of surface magnetism.     

Ultrafast magnon generation in an Fe film on Cu(100)

We report on a combined experimental and theoretical study of the spin-dependent relaxation processes in the electron system of an iron film on Cu(100). Spin-, time-, energy- and angle-resolved two-photon photoemission shows a strong characteristic dependence of the lifetime of photoexcited electrons on their spin and energy. Ab?initio calculations as well as a many-body treatment corroborate that the observed properties are determined by relaxation processes involving magnon emission. Thereby we demonstrate that magnon emission by hot electrons occurs on the femtosecond time scale and thus provides a significant source of ultrafast spin-flip processes. Furthermore, engineering of the magnon spectrum paves the way for tuning the dynamic properties of magnetic materials.     

Beitrag zur Kenntniss des Kobalts

Ohne Zusammenfassung     

Fast and solvent-free microwave-assisted synthesis of thermoresponsive oligo(glycidyl ether)s

Low-molecular weight linear poly(glycidyl ether)s are typically synthesized via the “classical,” oxy-anionic ring-opening polymerization (ROP) of glycidyl ether monomers at elevated temperatures. To reduce reaction times, a fast process was developed to synthesize oligo(glycidyl ether)s (OGEs) in bulk at a gram-scale utilizing microwave heating. Well-defined thermoresponsive copolymers comprising glycidyl methyl ether and ethyl glycidyl ether with molecular weights of up to 3 kDa were synthesized via microwave-assisted ROP with reaction times of approximately 10 min. The fast reaction kinetics were attributed to the rapid and uniform heating and high temperatures reached during the reaction. Consequently, no significant microwave-specific acceleration of the oxy-anionic ROP was observed. The temperature-triggered phase transition of the OGEs in aqueous solution revealed cloud point temperatures that are highly dependent on the OGE molecular weight, concentration, and comonomer composition, which extends previously reported data. Furthermore, oligo(glycidyl ether) acrylates (OGEAs) with reactive, functional end groups were directly accessible via in situ quenching of the anionic, microwave-assisted ROP with acrylic acid chloride. The obtained thermoresponsive OGEA macromonomers represent a promising material for the functionalization of surfaces via radical grafting methods to obtain functional, thermoresponsive coatings with potential application in cell culture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2496–2504     

Reaction of Dithiophosphoric Acid Chloride Betaine with Bifunctional Compounds - A New Route to Cyclic Dithiophosphates

Abstract

Dithiophosphoric acid chloride pyrididium betaine, Py. PS₂Cl (1)¹, can be widely used for the synthesis of various organophosphorus compounds. 1 reacts in the presence of a base with an excess of nucleophiles like amines, alcohols or thiols to the corresponding disubstituted thiophosphoric acid derivatives^2–3.