J. Zukrowski

Magnetoresistance in FeCoZr–Al2O3 nanocomposite films containing ‘metal core–oxide shell’ nanogranules

Temperature and magnetic field dependences of electrical conductivity are systematically studied in granular films (Fe45Co45Zr10)x(Al2O3)100?x (28???x???64) containing crystalline metallic ?-FeCo-based nanoalloy cores encapsulated in an amorphous oxide shell embedded in an amorphous Al2O3 matrix. Formation of ?metallic core?oxide shell? nanogranules is confirmed by transmission electron microscopy (TEM) and HRTEM. The structure of core and shell is governed with the difference in the oxidation states of Fe and Co ions investigated with EXAFS, XANES and M?ssbauer spectroscopy. A considerable negative magnetoresistance (MR) effect of spin-dependent nature is observed in the whole range of x values. Its increase with decreasing temperature is correlated with the magnetic saturation of superparamagnetic metallic nanogranules. The enhanced MR effect in ?core?shell? granular films is related to the percolation of oxide shells and their influence through spin filtering processes. A considerable high field MR at low temperatures and the resulting deviation of MR and squared magnetization are attributed to a magnetic randomness and/or strong magnetic anisotropy of the magnetic oxide shell.

Growth-induced non-planar magnetic anisotropy in FeCoZr-CaF2 nanogranular films: Structural and magnetic characterization

The relation between nanoscale structure, local atomic order and magnetic properties of (FeCoZr)x(CaF2)100−x (29 ≤ x ≤ 73 at. %) granular films is studied as a function of metal/insulator fraction ratio. The films of a thickness of 1–6 μm were deposited on Al-foils and glass-ceramic substrates, by ion sputtering of targets of different metal/insulator contents. Structural characterization with X-ray and electron diffraction as well as transmission electron microscopy revealed that the films are composed of isolated nanocrystalline bcc α-FeCo(Zr) alloy and insulating fcc CaF2 matrix. They grow in a columnar structure, where elongated metallic nanograins are arranged on top of each other within the columns almost normal to the substrate surface. Mossbauer spectroscopy and magnetometry results indicate that their easy magnetization axes are oriented at an angle of 65°–74° to the surface in films with x between 46 and 74, above the electrical percolation threshold, which is attributed to the growth-induced sh...

Spin reorientation in Er2Fe17−xMnx - Mössbauer effect study

The polycrystalline samples of Er2Fe17−xMnx compounds have been studied by57Fe Mossbauer spectroscopy in the temperature range between 4.2K and 200K. A reorientation of the easy axis of magnetization has been evidenced for compound with x=4 in the measurements on magnetically oriented powdered sample. Spin reorientation from the c-axis to the basal plane is observed when temperature is increased above 105K.

The influence of interstitial N, C and H atoms on the hyperfine fields at the yttrium and cobalt sites in Y2Co17

Abstract The spin echo nuclear magnetic resonance spectra of Y 2 Co 17 A x (A≡N, C, H) are presented. On the basis of the satellite pattern of the 89 Y spectra, we have deduced that N and C atoms occupy the 9e sites (rhombohedral compounds) or 6h sites (hexagonal compounds) around the yttrium site. A decrease in the hyperfine fields at the yttrium and cobalt sites caused by neighbouring interstitial atoms is observed, with a magnitude dependent on the site and the type of interstitial atom. The effect is discussed in terms of the influence of N, C and H atoms on the local electronic structure at the yttrium and cobalt sites and compared with the effect observed in the RE 2 Fe 17 -based compounds (RE, rare earth).

The influence of hydrogen on55Mn hyperfine fields in YMn2 hydrides

The NMR spin ccho measurements at 4.2 K for YMn2Hx (x=1, 2, 3) compounds are reported. The obtained values of55Mn hyperfine fields are analysed in dependence on the by hydrogen atoms and flips of neighbouring manganese moments. The strong increase of hyperfine field with increasing number of the nearest hydrogen atoms is explained by the change of orbital contribution to hyperfine field.