Exchange bias measurements of ferromagnetic/antiferromagnetic (F/AF) bilayers are typically performed with the magnetization of the F layer parallel to the AF interface. We describe measurements of Co/Pt multilayers with out-of-plane magnetic easy axis that are exchange biased with CoO. Field-cooling experiments with the applied field perpendicular and parallel to the sample plane exhibit loop shifts and enhanced coercivities. Modeling and comparison to biasing of samples with planar easy axis suggests such measurements provide a way to probe the spin projections at F/AF interfaces.

We have studied the magnetic switching behavior of exchange-coupled Fe 55 Pt 45 /Ni 80 Fe 20 films. On top of magnetically hard Fe 55 Pt 45 films having coercive fields up to 10 kOe were deposited soft magnetic NiFe films of different thickness values to form exchange-spring magnet structures. Magnetometry measurements exhibit the loop shapes characteristic of the exchange coupling between hard and soft magnetic phases; a reversible switching of the soft layer at low fields and an irreversible switching of the hard layer at higher fields. To investigate the switching behavior in more detail we prepared samples with 20-Å Co layers either deposited on top of the soft magnetic NiFe film or at the NiFe-FePt interface. Soft-x-ray magneto-optical Kerr effect measurements performed at the Co L-edge resonance allows us to use the Co layer as a local probe of the reversal process. The element-specific Kerr loops reveal that the reversible twist in the soft layer is not pinned rigidly at the interface but rather propagates significantly into the hard magnetic layer. As a consequence the reversible magnetization is not only stored in the soft layer, as often assumed. Additionally the major loops do not exhibit any well-defined switching field of the hard layer. Instead the results indicate that the irreversible switching of the hard phase evolves continuously with increasing external field in this materials system.

The polymerization of three vinylthiophene derivatives, 2-vinylthiophene (2VT), 3-vinylthiophene (3VT), and 2,5-dibromo-3-vinylthiophene (DB3VT), was carried out by reversible addition-fragmentation chain transfer (RAFT) process using six different chain transfer agents (CTAs). The novel doubly polymerizable monomer, DB3VT, undergoes controlled radical polymerization via the RAFT process, followed by Suzuki coupling reaction. Two dithiobenzoate-type RAFT agents, phenylethyl dithiobenzoate (CTA 2) and cumyl dithiobenzoate (CTA 3), were the most efficient to obtain poly(DB3VT) with controlled molecular weights and low polydispersities (M w /M n =1.05-1.15). Good control of the polymerization of DB3VT was confirmed by the linear increase in the molecular weight with the conversion and the ability to extend the chain by a second addition of the monomer. Chain extension from poly(methyl methacrylate) to DB3VT could be well controlled under suitable conditions and provided block copolymers having crosslinkable poly(DB3VT) segments with as-designed chain structures and low polydispersities. The block copolymers were also synthesized by RAFT polymerization of DB3VT using poly(methyl acrylate) as a macro-chain transfer agent (macro-CTA). Modifications of the 2,5-dibromide group of poly(DB3VT) by Suzuki coupling reaction using difunctional boronic acid afforded a network material, whereas a soluble composite having an extended π-structure was obtained by the coupling reaction of the block copolymer, poly(methyl methacrylate)-b-poly(DB3VT).

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