F. Tanczikó

Magnetic patterning perpendicular anisotropy FePd alloy films by masked ion irradiation

The nanopatterning of magnetic films by ion implantation is reported. Highly L10-ordered Fe47Pd53 epitaxial alloy films on a MgO(001) substrate were covered by a monolayer of silica spheres in a Langmuir film balance. Using this sphere layer as an implantation mask, the samples were irradiated by Ne+ or Fe+ ions with energies of 35 keV and 100 keV, respectively. After the silica mask was removed, the samples were characterized via conversion electron Mossbauer spectroscopy, longitudinal and polar magneto-optical Kerr effect, and atomic force and magnetic force microscopy. We find that the magnetic stripe domains observed in the nonirradiated sample were converted into a regular 2D magnetic pattern of hcp character upon 1 × 1015/cm2 35 keV neon or 1 × 1014/cm2 100 keV iron irradiation, with the direction of magnetization remaining out of plane in the nodes of the hcp lattice and relaxed into the film plane in the inter-node region, resulting in an overall in-plane magnetic softening of the film.

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...

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.

Angular dependence, blackness and polarization effects in integral conversion electron Mössbauer spectroscopy

Abstract General expressions of the electron yield in 57Fe integral conversion electron Mossbauer spectroscopy were derived depending on the glancing angle of the γ photons, on the source polarization and on the isotopic abundance of the source and the absorber (blackness effects) using an exponential escape function of the electrons originating from all Mossbauer-resonance-related processes. The present approach provides a firm theoretical basis to determine the alignment and direction of magnetization in the absorber. The intensity formulae were justified by least squares fits of α-57Fe spectral intensities measured in linearly and elliptically polarized source and absorber geometries. The fits reproduce the experimentally set angles with high accuracy. Limits of the current approach and its relation to other, less complete treatments in the literature are discussed.

Temperature dependence of the high-field magnetization in Fe-Ag granular alloys and discontinuous multilayers

Fe-Ag co-deposited granular alloy and discontinuous multilayer samples with 10-36 at% Fe average compositions were prepared by vacuum evaporation onto Si(111) single crystal substrates at room temperature. The magnetic properties of the samples were studied by SQUID and in-field Mossbauer spectroscopy. Superparamagnetic behaviour was observed for all the samples with blocking temperatures (TB) steeply increasing with increasing Fe concentration. The bulk magnetization (M) measured in 5 T shows linear temperature dependence for both types of samples, and the relative decrease with temperature is much larger for a granular alloy than for a multilayer sample of equal TB. The Mossbauer spectroscopy results indicate that the faster decrease of the high field magnetization in granular alloys is explained by the larger amount of small grains that are not aligned by the 5 T field.