D. G. Merkel

Modification of local order in FePd films by low energy He+ irradiation

Owing to their strong perpendicular magnetic anisotropy, FePd, CoPd, and their Co(Fe)Pt counterparts are candidate materials for ultrahigh density magnetic recording. The stability and magnetic properties of such films are largely dependent on the orientation and local distribution of the L10 FePd phase fraction. Therefore, the formation and transformation of the L10 phase in such thin films have been the subject of continued interest. Highly ordered epitaxial FePd(001) thin films (with an L10 phase fraction of 0.81) were prepared by molecular-beam epitaxy on a MgO(001) substrate. The effect of postgrown room temperature, 130 keV He+ irradiation was investigated at fluences up to 14.9×1015 ions/cm2. X-ray diffraction and conversion electron Mossbauer spectroscopy revealed that with increasing fluence, the L10 FePd phase decomposes into the face centered cubic phase with random Fe and Pd occupation of the sites. A partially ordered local environment exhibiting a large hyperfine magnetic field also develops...

Disentangling magnetic order on nanostructured surfaces

We present a synchrotron-based X-ray scattering technique which allows disentangling magnetic properties of heterogeneous systems with nanopatterned surfaces. This technique combines the nmrange spatial resolution of surface morphology features provided by Grazing Incidence Small Angle X-ray Scattering and the high sensitivity of Nuclear Resonant Scattering to magnetic order. A single experiment thus allows attributing magnetic properties to structural features of the sample; chemical and structural properties may be correlated analogously. We demonstrate how this technique shows the correlation between structural growth and evolution of magnetic properties for the case of a remarkable magnetization reversal in a structurally and magnetically nanopatterned sample system.

Isotope-periodic multilayer method for short self-diffusion paths - A comparative neutron and synchrotron Mössbauer reflectometric study of FePd alloys

FePt, FePd, CoPt, and CoPd in equilibrium exhibit the L10 structure with high perpendicular magnetic anisotropy making them attractive candidates for high-density magnetic recording. Magnetic properties of these films depend on the distribution and orientation of the L10 fraction controlled by diffusion on atomic scale. Epitaxial isotope-periodic natFePd/57FePd alloy films were prepared by molecular beam epitaxy and heat treated at 500?C for various retention times. Isotope-sensitive non-destructive methods, neutron reflectometry and synchrotron M?ssbauer reflectometry were applied to follow very short diffusion paths normal to the film plane. Squared diffusion lengths and diffusion profiles were obtained from the fitting of experimental reflectivity curves for each annealing treatment steps. The somewhat different diffusion lengths obtained for the neutron and synchrotronM?ssbauer reflectograms of the same samples are explained by the larger footprint of the sample in the neutron experiment for which interface inhomogeneities are to be averaged. Diffusion in the microscopically different local environments were modelled by piecewise constant diffusion coefficients in the regions identified as different species by conversion electron M?ssbauer spectroscopy.

Realizing total reciprocity violation in the phase for photon scattering

Reciprocity is when wave or quantum scattering satisfies a symmetry property, connecting a scattering process with the reversed one. While reciprocity involves the interchange of source and detector, it is fundamentally different from rotational invariance, and is a generalization of time reversal invariance, occurring in absorptive media as well. Due to its presence at diverse areas of physics, it admits a wide variety of applications. For polarization dependent scatterings, reciprocity is often violated, but violation in the phase of the scattering amplitude is much harder to experimentally observe than violation in magnitude. Enabled by the advantageous properties of nuclear resonance scattering of synchrotron radiation, we have measured maximal, i.e., 180-degree, reciprocity violation in the phase. For accessing phase information, we introduced a new version of stroboscopic detection. The scattering setting was devised based on a generalized reciprocity theorem that opens the way to construct new types of reciprocity related devices.

Erratum: Lattice Dynamics of EuO: Evidence for Giant Spin-Phonon Coupling [Phys. Rev. Lett. 116 , 185501 (2016)]

This corrects the article DOI: 10.1103/PhysRevLett.116.185501.