B. Stahl

Structure and magnetic properties of iron nanoparticles stabilized in carbon

Nanoparticles composed of iron and carbon have been produced by chemical vapor synthesis. A detailed structural, electronic, and magnetic characterization has been performed by several methods. The atomic arrangement in the as-prepared particles is strongly affected and stabilized by excess carbon. Small clusters of different ferrous phases are the building blocks of the particles. Due to the in situ formation of a carbonaceous shell the particles are stable against oxidation at ambient conditions. The magnetic properties are influenced by the exceptionally small particle size. The particles exhibit superparamagnetic behavior with a blocking temperature of 30K and the temperature dependence of the magnetization is governed by the finite size of the system.

Depth selective CEMS in the energy range 0 to 20 keV

Abstract The “depth selectivity” can be expressed by weight functions TE,Θ(x) giving the probability that electrons, starting in depth x, reach and leave the surface with an energy E, and an emission angle Θ relative to the surface normal. TE,Θ(x) was available up to now only for K conversion electrons of iron in the energy range 6.3–7.3 keV. To extend the available depth range for 57Fe DCEMS, we calculated TE,Θ(x) for energies down to about 2 keV, and up to 14.4 keV, including K, L and M conversion and KLL Auger electrons. Based on these results a program has been developed to simulate for a given sample composition DCEMS and also ICEMS spectra. First results of electron transport calculations for the 19.6 keV L conversion electrons of 119Sn indicate a reduced surface sensitivity in comparison to 57Fe, but the depth resolution seems to be reasonably good for deep layers.

Interface contribution to giant magnetoresistance in granular AgFe studied with Mössbauer spectroscopy

The magnetotransport properties of granular thin AgFe films, prepared by codeposition of the constituent metals in an ultrahigh vacuum have been investigated. Mossbauer spectroscopy was employed to investigate the role of scattering of conduction electrons at the interface between the magnetic Fe particles and the Ag matrix. It is possible to determine the ratio of Fe atoms located at the Ag/Fe interface and in the particles (bulk atoms). The giant magnetoresistance effect correlates with the ratio of interface/bulk atoms.

Implantation induced phase formation in stainless steel

Abstract After Eu implantation, the phase formation in a surface region of 150 nm of stainless steel was studied non-destructively by a depth resolved Mossbauer technique (DCEMS). The observed iron phases are characterized by the hyperfine interaction of the 57 Fe nuclei. Their characteristics and depth distributions strongly depend on fluence and ion energy. A newly formed martensitic phase accompanies the implantation profile of the Eu atoms into a depth of up to about 120 nm. In a near-surface region of 15 nm, the observed phases differ from those found in larger depths. This reveals the substantial role of the surface, where implantation induced diffusion and segregation processes are effective. Concerning the DCEMS analysis, special emphasis is laid on the determination of systematic and statistical errors of the phase depth profiles.

DEPTH RESOLVING PHASE ANALYSIS OF ION IMPLANTED STAINLESS STEEL

Abstract For a better understanding of the complex process of ion implantation the information on the composition in phases as a function of depth within the implanted area is needed. In the present work a high austenitic stainless steel of composition Fe62Ni20Cr18 was implanted with 400 keV 151Eu ions with different doses up to 1.2 × 1017 ions/cm2. The depth profile of phases was determined by depth selective conversion electron Mossbauer spectroscopy (DCEMS). We observed a martensitic phase within a region of depth, that coincides with the elemental depth profile of the implanted Eu measured by Rutherford backscattering spectroscopy. Furthermore in connection with the DCEMS results the strong influence of adsorbate layers on the formation of the depth profile and phases will be discussed.

Micromagnetic Aspects of Magnetoreception of Homing Pigeons Based on Iron Minerals

The identification of ferrimagnetic iron minerals in the skin of the upper beak of homing pigeons poses fundamental questions on the principles at work in magnetoreception. Aspects concerning the type of mineral, the size, shape and arrangement of the particles are discussed on grounds of micromagnetic simulations.

Antiferromagnetic exchange coupling in amorphous Fe–Sc alloys

AbstractResults of 57Fe Mössbauer, AC and DC susceptibility, grazing incidence X-ray diffraction, resistivity and Rutherford-backscattering measurements on the amorphous alloys % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbWexLMBb50ujbqeguuD% JXwAKbqee0evGueE0jxyaibaieYlf9irVeea0dXdh9vqqj-hEeea0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciGacaqaaeaadiqaaqaaaO% qaaiaabAeacaqGLbWaaSbaaSqaaiaaigdacaaIWaGaaGimaiabgkHi% TGWaciab-Hha4bqabaGccaqGtbGaae4yamaaBaaaleaacqWF4baEae% qaaOGaaeiiaiaacIcacaaI4aWexLMBbXgBd9gzLbvyNv2CaeXbtLwB% tvNBaGqbaiaa+rMicqWF4baEcaGFKjIaaG4naiaaicdacaGGPaaaaa!5255!

GMR in Granular CuFe with a Face Centered Tetragonal Structure of Iron

{\text{Fe}}_{100 - x} {\text{Sc}}_x (8 \leqslant x \leqslant 70)