Jolanta Stankiewicz

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.2 nm (25\char21{}7000 atoms) prepared by sequential sputtering of Co and

GIANT MAGNETORESISTANCE NEAR THE MAGNETOSTRUCTURAL TRANSITION IN GD5(SI1.8GE2.2)

{\mathrm{Al}}_{2}{\mathrm{O}}_{3}.

Magnetotransport through the spin-reorientation transition in Tm2Fe14B

The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared with previous structural characterizations. The distribution of activation energies has been independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant

Study of the phase transitions in

{K}_{\mathrm{eff}}.

p-type conduction in sputtered indium oxide films

We find that

The metal - insulator transition in perovskites

{K}_{\mathrm{eff}}

Electroreflectance and wavelength‐modulated reflectivity spectra of Zn1−xMnxSe alloys

is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal process is shown to proceed classically down to the lowest temperature investigated (1.8 K).

Kondo physics in a rare earth ion with well localized 4f electrons

Zero-field electrical resistivity over the temperature range of 4–300 K and magnetoresistance in magnetic fields of up to 12 T have been measured in Gd5(Si1.8Ge2.2). This system undergoes a first-order magnetostructural transition at TC≅240 K, from a high-temperature paramagnetic to a low-temperature ferromagnetic phase, accompanied by a large drop in the resistivity. The application of an external magnetic field above TC can induce this transition, and a giant negative magnetoresistance effect (Δρ/ρ≅−20%) is observed associated with this first-order field-induced transition.

Temperature and composition dependence of the energy gap in Cd1−xFexSe

The electrical resistivity and Hall effect for a single crystal of Tm2Fe14B have been measured over the range of temperature (T) from 4 to 600 K in magnetic fields of up to 5 T. The resistivity exhibits a small step-like rise at the spin-reorientation temperature Ts, which is 311 K, and a broad minimum at 535 K. In addition, the Hall coefficient shows an anomaly at Ts, and drops sharply as T approaches the Curie temperature (549 K) from below. The lower-temperature anomalies, both in the resistivity and in the Hall coefficient, show that the spin-reorientation transition in Tm2Fe14B is of first order. The high-temperature Hall anomaly is probably produced by critical spin fluctuations near the Curie point. Dominant scattering mechanisms that underlie the Hall effect and magnetoresistance in Tm2Fe14B are inferred.

PHOTOCONDUCTIVITY STUDIES IN CD1-XFEXSE

has been synthesized under high oxygen pressure from a precursor prepared by means of a sol-gel method. The material obtained is of single phase and has an orthorhombic crystal structure at room temperature. The magnetic, electrical and thermal properties have been measured over a wide temperature range. This compound exhibits a metal-insulator and a paramagnetic-antiferromagnetic transition at 400 K and at 220 K, respectively. The metal-insulator transition is of first order while the magnetic ordering is a second order transition as can be inferred from calorimetric measurements. In addition, we observe an anomaly in the resistivity near the Neel temperature indicating a change in the conduction mechanism at this temperature. Our results support local antiferromagnetic correlations above the Neel temperature for this compound.