282 research outputs found
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 , and the N\'{e}el temperature of an antiferromagnet
, the inducing temperature , 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 and . Physics and experimental approaches to measure the
inducing temperature are discussed. Measurements of , in addition to
, and , provide important information about exchange interactions
in ferromagnetic - antiferromagnetic heterostructures
Meissner-London susceptibility of superconducting right circular cylinders in an axial magnetic field
Magnetic susceptibility of non-ellipsoidal samples is a long-standing problem
in experimental studies of magnetism and superconductivity. Here the
quantitative description of the Meissner-London response (no Abrikosov
vortices) of right circular cylinders in an axial magnetic field is given. The
three-dimensional adaptive finite-element modeling was used to calculate the
total magnetic moment, m, in a wide range of London penetration depth, \lambda,
to sample size ratios. By fitting the numerical data, the closed-form universal
magnetic susceptibility is formulated involving only sample dimensions and
\lambda, thus providing a recipe for determining the London penetration depth
from the accurate magnetic susceptibility measurements. Detailed examples of
the experimental data analysis using the developed approach are given. The
results can be extended to the frequently used cuboid-shaped samples
Linear magnetic susceptibility of anisotropic superconductors of cuboidal shape
A simplified model of anisotropic magnetic susceptibility in the
Meissner-London vortex-free state of cuboidal superconducting samples is
presented. Using this model, precision measurements of the magnetic response in
three perpendicular directions of a magnetic field with respect to primary
crystal axes, can be used to extract the components of the London penetration
depth, thus enabling the evaluation of the general superfluid density tensor,
which is needed in the analysis of the superconducting gap structure.Comment: Accepted in Journal of Applied Physics: Methods. arXiv admin note:
text overlap with arXiv:2101.0648
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
Superconducting Nanocomposites: Enhancement of Bulk Pinning and Improvement of Intergrain Coupling
Heterogeneous sonochemical method was applied for synthesis of novel
superconducting nanocomposites consisting of magnetic (and/or nonmagnetic)
nanoparticles embedded into the bulk of ceramic superconductors. In addition to
in-situ production of the efficient pinning centers, this synthesis method
considerably improves the interbrain coupling. Significant enhancement of the
magnetic irreversibility is reported for Fe2O3 nanoparticles embedded into the
bulk of MgB2 superconductor. Nonmagnetic Mo2O5 nanoparticles also increase
pinning strength, but less than magnetic Fe2O3. Detailed magnetization and
electron microscopy characterization is presented. Theory of bulk magnetic
pinning due to ferromagnetic nanoparticles of finite size embedded into the
superconducting matrix is developed
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
Effective Demagnetizing Factors of Diamagnetic Samples of Various Shapes
Effective demagnetizing factors that connect the sample magnetic moment with the applied magnetic field are calculated numerically for perfectly diamagnetic samples of various nonellipsoidal shapes. The procedure is based on calculating the total magnetic moment by integrating the magnetic induction obtained from a full three-dimensional (3D) solution of the Maxwell equations using an adaptive mesh. The results are relevant for superconductors (and conductors in ac fields) when the London penetration depth (or the skin depth) is much smaller than the sample size. Simple but reasonably accurate approximate formulas are given for practical shapes including rectangular cuboids, finite cylinders in axial and transverse fields, as well as infinite rectangular and elliptical cross-section strips
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
- …