Effective collective barrier for magnetic relaxation in frozen ferrofluids

Magnetic relaxation and frequency response were measured in frozen ferrimagnetic colloids of different concentrations. A crossover from reversible to irreversible behavior is observed for concentrated colloids. In irreversible state, magnetic relaxation is time-logarithmic over seven orders of magnitude of experimental time windows. A master curve construction within mean field phenomenological model is applied to extract effective collective barrier as a function of the irreversible magnetization. The barrier logarithmically diverges, providing evidence for self-organized critical behavior during magnetic relaxation in frozen ferrofluids

Sonochemical Modification of the Superconducting Properties of MgB2

Ultrasonic irradiation of magnesium diboride slurries in decalin produces material with significant inter-grain fusion. Sonication in the presence of Fe(CO)5 produces magnetic Fe2O3 nanoparticles embedded in the MgB2 bulk. The resulting superconductor-ferromagnet composite exhibits considerable enhancement of the magnetic hysteresis, which implies an increase of vortex pinning strength due to embedded magnetic nanoparticles

Characteristic temperatures of exchange biased systems

Characteristic temperatures in ferromagnetic - antiferromagnetic exchange biased systems are analyzed. In addition to usual blocking temperature of exchange bias $T_{B}$, and the N\'{e}el temperature of an antiferromagnet $T_{N}$, the inducing temperature $T_{ind}$, i.e., the temperature, at which the direction of exchange anisotropy is established, has been recently proposed. We demonstrate that this temperature is in general case different from $T_{B}$ and $T_{N}$. Physics and experimental approaches to measure the inducing temperature are discussed. Measurements of $T_{ind}$, in addition to $T_{B}$, and $T_{N}$, provide important information about exchange interactions in ferromagnetic - antiferromagnetic heterostructures

Effects of High Intensity Ultrasound on BSCCO-2212 Superconductor

Slurries of powdered Bi2Sr2CaCu2O8+x superconductor in low volatility alkanes were treated with intense ultrasound. Significant enhancements of magnetic irreversibility as well as transport critical current are reported. The effects are dependent on the concentration of the slurry and are optimal for 1.5% wt. slurry loading. Electron microscopy shows that ultrasonic treatment leads to a change in grain morphology and intergrain welding. The observed enhancement of superconducting properties is consistent with the limitations in critical currents in BSCCO superconductor being due to intergrain coupling rather than intragrain pinning strength.Comment: 3 page