We have studied the evolution of the magnetic state of a nanometer thick antiferromagnetic (AFM) FeO layer during its formation using nuclear resonant scattering of synchrotron radiation. In contact to ferromagnetic Fe, the FeO layer does not show magnetic order at room temperature (RT). Once embedded between two Fe layers, magnetic coupling to the adjacent ferromagnets leads to a drastic increase of the Néel temperature far above RT, while the blocking temperature remains below 30 K. The presented results evidence the role that the ferromagnetic surrounding plays in modifying the magnetic state of ultrathin AFM layers. DOI: 10.1103/PhysRevLett.103.097201 PACS numbers: 75.70.Cn, 75.25.+z, 75.75.+a, 76.80.+y Magnetic data storage technology is reaching the bottom of the nanoscale. The stabilization of magnetic order in low-dimensional structures becomes a key issue. Below a critical thickness, ferromagnets undergo a superparamagnetic relaxation where spins are thermally excited, and the system does not show magnetic hysteresis anymore. Exchange bias bilayer systems composed of a ferromagnet (FM) and an antiferromagnet (AFM) have been recently reported to substantially reduce the critical thickness under which the ferromagnet undergoes superparamagnetic relaxation [1,2]. Layered FM/AFM systems, where an AFM layer (with high anisotropy) is used to pin the magnetization of the FM, are used to create reference magnetic layers in devices. Below a certain temperature (the blocking temperature T B ) the spins in the antiferromagnet are frozen and exchange coupling at the FM/AFM interface leads to a shift of the hysteresis loop and an increase of the coercivity, this phenomenon being known as the exchange bias effect [3,4].In the ultrathin film limit, the thermal stability of these FM/AFM bilayers is strongly modified [5,6]. In exchange bias systems, one usually distinguishes the Néel (ordering) temperature T N of the antiferromagnet and the blocking temperature T B below which exchange bias occurs [7]. For thick AFM layers (> 50 nm), T N and T B are usually found to be equivalent. Field cooling the system below T N directly leads to the freezing of spins (and the appearance of exchange bias). Early studies showed that T B was usually decreasing with decreasing thickness of the AFM layer, and it was assumed that T N was decreasing accordingly due to a finite size effect [5]. Recently, Vallejo-Fernandez et al. found out that the evolution of the exchange bias field H e and T B for polycrystalline films was in fact linked to the average grain volume of the AFM [6], which typically decreases with the layer thickness. This results in a decreased stability against thermal excitation and a decrease of T B . It should be noted that there is still an underlying physics problem as data on epitaxially grown AFM/FM bilayers also show a reduction of T B with a decreasing AFM layer thickness [8,9]; this is still the subject of different theoretical considerations [5,10]. The evolution of T N relative to T B was investigated by Va...

We present a detailed study of the magnetic and structural properties of L1 0 -FePt thin films. The films are prepared via molecular beam epitaxy directly onto MgO͑001͒ substrates, i.e., without buffer layer. Despite the large lattice misfit between the in-plane lattice parameters of L1 0 FePt and MgO, highly ordered thin films are obtained with the easy magnetization c axis perpendicular to the film plane. Via high resolution transmission electron microscopy and Rutherford backscattering measurements we focus on the FePt/MgO interface to study the misfit relaxation and the defect density. Further, the influence of elevated substrate temperatures and of postgrowth high temperature annealing on the structural and magnetic properties is discussed.

We studied the exchange-spring behavior in FePt-Fe hard-soft magnetic heterostructures. We present a study of the spin structure of the soft Fe layer of Fe-FePt bilayers by nuclear forward scattering of synchrotron radiation. The orientation of the Fe moments close to the top of the soft layer was determined quantitatively as a function of the soft-layer thickness. We show that for a few monolayers of Fe, the magnetically hard FePt layer pins the magnetization in the soft Fe layer to the out-of-plane direction. With increasing Fe-layer thickness, the influence of the FePt diminishes and the magnetization cants toward the in-plane Fe͓001͔ direction. The significance of the exchange coupling constant as the relevant parameter for the exchange-spring behavior is demonstrated by one-dimensional micromagnetic simulations.

We employed nuclear inelastic scattering of synchrotron radiation to measure the anisotropy in the phonon density of states of an FePt thin film ordered in the L1 0 phase and compared our results with ab initio calculations. We find a strong anisotropy in the phonon density of states along the a and c axes of the crystal, which induces a difference in the calculated thermodynamic and elastic parameters along these axes. Calculations of surface-related effects show that a strong deviation from the bulk vibrational spectrum is observed for an Fe-terminated surface. We deduce by comparison with our surface sensitive measurement that the FePt͑100͒-oriented surface is Pt terminated. This contrasts with a recent measurement on FePt nanoparticles, where additional low-energy modes are observed. The findings are expected to be representative of the lattice dynamics of L1 0 intermetallics.

This paper describes the principle and performance of FlexRay, a fully programmable illuminator for high NA immersion systems. Sources can be generated on demand, by manipulating an array of mirrors instead of the traditional way of inserting optical elements and changing lens positions. On demand (freeform) source availability allows for reduction in R&D cycle time and shrink in k1. Unlimited tuning allows for better machine to machine matching. FlexRay has been integrated in a 1.35NA TWINSCAN exposure system. We will present data of FlexRay using measured traditional and freeform illumination sources. In addition system performance qualification data on stability, reproducibility and imaging will be shown. The benefit of FlexRay for SMO enabling shrink is demonstrated using an SRAM example.