arXiv subjects

Nurit Avraham

Publications and source records attributed to Nurit Avraham.

23 records · Page 2Linked to original sources

arXiv2007

Angular dependence of the melting of the porous vortex matter in $\mathrm{Bi_{2}Sr_{2}CaCu_{2}O_{8}}$

The behavior of vortex matter in $\mathrm{Bi_{2}Sr_{2}CaCu_{2}O_{8}}$ in the presence of a low concentration of tilted columnar defects (CDs) was studied using magneto-optical measurements and molecular dynamics simulations. We find that while the dynamic properties are significantly affected by tilting the field away from CDs, the thermodynamic lines are angle independent. Our simulations reveal that vortex pancakes remain localized along CDs even at large tilting angles thus preserving the thermodynamic features, while suppression of irreversible properties is caused by vortex kink sliding.

cond-mat.supr-con↗

arXiv2005

Propagation of Avalanches in Mn$_{12}$-acetate: Magnetic Deflagration

Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly two orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.

cond-mat.other↗

arXiv2005

Local Measurements of Magnetization in Mn12 Crystals

The spatial profile of the magnetization of Mn12 crystals in a swept magnetic field applied along the easy axis is determined from measurements of the local magnetic induction along the sample surface using an array of Hall sensors. We find that the magnetization is not uniform inside the sample, but rather shows some spatial oscillations which become more prominent around the resonance field values. Moreover, it appears that different regions of the sample are at resonance at different values of the applied field and that the sweep rate of the internal magnetic induction is spatially non-uniform. We present a model which describes the evolution of the non-uniformities as a function of the applied field. Finally we show that the degree of non-uniformity can be manipulated by sweeping the magnetic field back and forth through part of the resonance.

cond-mat.mes-hall↗

arXiv2002

First-order disorder-driven transition and inverse melting of the vortex lattice

Vortex matter phase transitions in the high-temperature superconductor Bi2Sr2CaCu2O8 were studied using local magnetization measurements combined with a vortex 'shaking' technique. The measurements revealed thermodynamic evidence of a first-order transition along the second magnetization peak line, at temperatures below the apparent critical point Tcp. We found that the first-order transition line does not terminate at Tcp, but continues down to at least 30 K. This observation suggests that the ordered vortex lattice phase is destroyed through a unified first-order transition that changes its character from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures. At intermediate temperatures the transition line shows an upturn, which implies that the vortex matter displays 'inverse' melting behavior.

cond-mat.supr-con↗

arXiv2001

Inverse melting of the vortex lattice

Inverse melting, in which a crystal reversibly transforms into a liquid or amorphous phase upon decreasing the temperature, is considered to be very rare in nature. The search for such an unusual equilibrium phenomenon is often hampered by the formation of nonequilibrium states which conceal the thermodynamic phase transition, or by intermediate phases, as was recently shown in a polymeric system. Here we report a first-order inverse melting of the magnetic flux line lattice in Bi2Sr2CaCu2O8 superconductor. At low temperatures, the material disorder causes significant pinning of the vortices, which prevents observation of their equilibrium properties. Using a newly introduced 'vortex dithering' technique we were able to equilibrate the vortex lattice. As a result, direct thermodynamic evidence of inverse melting transition is found, at which a disordered vortex phase transforms into an ordered lattice with increasing temperature. Paradoxically, the structurally ordered lattice has larger entropy than the disordered phase. This finding shows that the destruction of the ordered vortex lattice occurs along a unified first-order transition line that gradually changes its character from thermally-induced melting at high temperatures to a disorder-induced transition at low temperatures.

cond-mat.supr-con↗