Magnetic and Transport Properties of Fe-Ag granular multilayers

Results of magnetization, magnetotransport and Mossbauer spectroscopy measurements of sequentially evaporated Fe-Ag granular composites are presented. The strong magnetic scattering of the conduction electrons is reflected in the sublinear temperature dependence of the resistance and in the large negative magnetoresistance. The simultaneous analysis of the magnetic properties and the transport behavior suggests a bimodal grain size distribution. A detailed quantitative description of the unusual features observed in the transport properties is given

Dipole–dipole interaction in superparamagnetic nanocrystalline Fe63.5Cr10Si13.5B9Cu1Nb3

Cr-substituted Finemet-type nanocrystalline alloy (Fe63.5Cr10Si13.5B9Cu1Nb3) has been studied by differential scanning calorimetry, x-ray diffraction, Mo¨ssbauer spectroscopy, and magnetic measurements. The Curie temperature of the remaining amorphous phase decreases as the crystalline volume fraction increases, reaching values below room temperature. This feature makes the alloy adequate for studying the magnetic decoupling of the ~Fe,Si! nanocrystals at moderated temperatures and, in particular, the superparamagnetic relaxation in broad temperature and crystalline fraction ranges. It was shown that the anomalous dependence of the coercive field on the annealing temperature can be satisfactorily explained assuming a dipolar-type interaction between the crystallites.DGES del Gobierno español-PB97-1119-CO2-01Fondo de investigación del gobierno húngaro-OTKA T-030753Academia de Ciencias de Hungría-AKP 98-25 2,

Tailoring Fe/Ag Superparamagnetic Composites by Multilayer Deposition

The magnetic properties of Fe/Ag granular multilayers were examined by SQUID magnetization and Mossbauer spectroscopy measurements. Very thin (0.2 nm) discontinuous Fe layers show superparamagnetic properties that can be tailored by the thickness of both the magnetic and the spacer layers. The role of magnetic interactions was studied in novel heterostructures of superparamagnetic and ferromagnetic layers and the specific contribution of the ferromagnetic layers to the low field magnetic susceptibility was identified.Comment: 5 pages and 3 figure

Memory effect in Fe-Ag granular multilayers

Magnetic memory effect was measured in Fe-Ag granular multilayers by employing the so-called stop-and-wait protocol in order to reveal super-spin glass (SSG) behavior and explore the role of intra- and interlayer interactions which can influence the superparamagnetic (SPM) behavior of Fe particles separated by Ag layers. Calculations based on the relaxation of two-level systems are made to obtain the evolution of the magnetization of interaction-free SPM particles as a function of temperature and time for arbitrary annealing procedures, e.g., zero-field-cooled (ZFC) and field-cooled (FC) susceptibility (low-field magnetization) or temperature-cycling measurements. In samples with a single Fe layer of different nominal thicknesses, both the observed memory effect and the low-temperature deviation of the measured FC magnetization from the calculated interaction-free FC curve are attributed to the effect of dipolar interactions. Estimates on the anisotropy energy suggest the importance of the surface anisotropy of the Fe particles in the magnetic behavior

Average Magnetization and Fe Hyperfine Fields in Co₂FeSi-based Heusler Alloys

In the present study SQUID magnetic and $\text{}^{57}Fe$ Mössbauer measurements were performed on bulk $Co₂FeAl_{1-x}Siₓ$, $Co₂Fe_{0.9}TM_{0.1}Si$ (TM = Ti, V, Cr, Mn, Co, Ni, Cu), $Co_{2-y}Fe_{1+y}Si$ and $Co₂Fe_{1+z}Si_{1-z}$ samples prepared by induction melting. The $Co₂FeAl_{1-x}Siₓ$ shows the L2₁ crystal structure only for x ≥ 0.5, between x = 0 and 0.3 it has the B2 structure (Fe-Al, Si disorder). The average magnetization of these alloys does not follow the expected Slater-Pauling trend (on the Si side saturation is observed around 5.75 $μ_{B}$/f.u.) and similar deviation is observed for the replacement of Fe by transition metal (TM) atom. The effect of the antisite disorder (Fe-Si) on the magnetization and Fe hyperfine parameters was determined and significant decrease in the Co magnetic moment for excess Si neighbourhood is extrapolated. The formerly reported large ≈ 6 $μ_{B}$/f.u. magnetization for Co₂FeSi was observed only in samples having Fe excess and Si deficiency