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 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.

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 present a critical comparison between conventional Mössbauer spectroscopy on the one hand and energy and time resolved nuclear resonant scattering on the other hand. The three Mössbauer techniques are evaluated by the characterization of the complex magnetic structure of an Fe3Al alloy. It is shown how the different scattering processes and detection schemes, which are involved in the respective configurations, determine the specific strengths of the three techniques and how they are optimally suited for the characterization of materials of varying complexity and reduced sizes.

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