arXiv subjects

D. S. F. Crothers

Publications and source records attributed to D. S. F. Crothers.

3 recordsLinked to original sources

arXiv2000

Pair production and electron capture in relativistic heavy-ion collisions

Results are presented for simulations of electron-positron pair production in relativistic heavy-ion collisions leading to electron capture and positron ejection. We apply a two-center relativistic continuum distorted-wave model to represent the electron/positron dynamics during the collision process. The results are compared with experimental cross-section data for ${\rm La}^{57+}$ and ${\rm Au}^{79+}$ impact on Gold, Silver and Copper targets. The theory is in very good agreement with experiment, verifying the result that the process increases in importance with both collision energy and target atomic number, and improves upon previous simulations of this process.

physics.atom-ph↗

arXiv2000

Thermally activated escape rates of uniaxial spin systems with transverse field

Classical escape rates of uniaxial spin systems are characterized by a prefactor differing from and much smaller than that of the particle problem, since the maximum of the spin energy is attained everywhere on the line of constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is applied, a saddle point of the energy is formed, and high, moderate, and low damping regimes (similar to those for particles) appear. Here we present the first analytical and numerical study of crossovers between the uniaxial and other regimes for spin systems. It is shown that there is one HD-Uniaxial crossover, whereas at low damping the uniaxial and LD regimes are separated by two crossovers.

cond-mat.stat-mech↗

arXiv2000

Field dependence of the temperature at the peak of the ZFC magnetization

The effect of an applied magnetic field on the temperature at the maximum of the ZFC magnetization, $M_{ZFC}$, is studied using the recently obtained analytic results of Coffey et al. (Phys. Rev. Lett. {\bf 80}(1998) 5655) for the prefactor of the Néel relaxation time which allow one to precisely calculate the prefactor in the Néel-Brown model and thus the blocking temperature as a function of the coefficients of the Taylor series expansion of the magnetocrystalline anisotropy. The present calculations indicate that even a precise determination of the prefactor in the Néel-Brown theory, which always predicts a monotonic decrease of the relaxation time with increasing field, is insufficient to explain the effect of an applied magnetic field on the temperature at the maximum of the ZFC magnetization. On the other hand, we find that the non linear field-dependence of the magnetization along with the magnetocrystalline anisotropy appears to be of crucial importance to the existence of this maximum.

cond-mat↗