Showing papers by "Myriam P. Sarachik published in 1996"

Macroscopic measurement of resonant magnetization tunneling in high-spin molecules

Abstract: We report the observation of steps at regular intervals of magnetic field in the hysteresis loop of a macroscopic sample of oriented M${\mathrm{n}}_{12}$${\mathrm{O}}_{12}$(C${\mathrm{H}}_{3}$COO${)}_{16}$(${\mathrm{H}}_{2}$O${)}_{4}$ crystals. The magnetic relaxation rate increases substantially when the field is tuned to a step. We propose that these effects are manifestations of thermally assisted, field-tuned resonant tunneling between quantum spin states, and attribute the observation of quantum-mechanical phenomena on a macroscopic scale to tunneling in a large (Avogadro's) number of magnetically identical molecules.

Electric Field Scaling at a B=0 Metal-Insulator Transition in Two Dimensions.

Abstract: The nonlinear (electric field-dependent) resistivity of the 2D electron system in silicon exhibits scaling as a function of electric field and electron density in both the metallic and insulating phases, providing further evidence for a true metal-insulator transition in this 2D system at $B\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$. Comparison with the temperature scaling yields separate determinations of the correlation length exponent, $\ensuremath{ u}\ensuremath{\approx}1.5$, and the dynamical exponent, $z\ensuremath{\approx}0.8$, close to the theoretical value $z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$.

Steps in the hysteresis loops of a high-spin molecule

Abstract: We report the first observation of steps in the hysteresis loop of a high‐spin molecular magnet. We propose that the steps, which occur every 0.46 T, are due to thermally assisted resonant tunneling between different quantum spin states. Magnetic relaxation increases dramatically when the field is in the neighborhood of a step. A simple model accounts for the observations and predicts a value for the anisotropy barrier consistent with that inferred from the superparamagnetic blocking temperature.

Magnetic-field-induced crossover from Mott variable-range hopping to weakly insulating behavior

Abstract: In three-dimensional n-CdSe samples that obey Mott variable-range hopping, \ensuremath{\rho}=${\mathrm{\ensuremath{\rho}}}_{0}$exp(${\mathit{T}}_{0}$/T${)}^{1/4}$, in the absence of a magnetic field, we report a field-induced crossover at low temperatures to a resistivity that exhibits a weak power-law divergence, \ensuremath{\rho}=${\mathrm{\ensuremath{\rho}}}_{0}$${\mathit{T}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\alpha}}}$, with an exponent \ensuremath{\alpha} that decreases slowly with increasing field. \textcopyright{} 1996 The American Physical Society.

Resonant tunneling of magnetization in Mn12 acetate complex

Abstract: Based on low-temperature measurements on oriented crystallites of Mn12 acetate complex, we report strong evidence for resonant tunneling of magnetization for these high spin molecules: we observed periodic steps in the hysteresis loops, periodic marked peaks in the magnetic relaxation rate at the fields corresponding to these steps, and a concomitant periodic decrease of the blocking temperature with magnetic field. We attribute these observations to thermally assisted resonant tunneling of the magnetization in a double well potential and propose a detailed model to account for our results.