  Static and dynamic behavior of short-range Ising-spin glass
Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compounds
(GBIC) has been studied with SQUID DC and AC magnetic susceptibility. The $T$
dependence of the zero-field relaxation time $\tau$ above a spin-freezing
temperature $T_{g}$ (= 3.92 $\pm$ 0.11 K) is well described by critical slowing
down. The absorption $\chi^{\prime\prime}$ below $T_{g}$ decreases with
increasing angular frequency $\omega$, which is in contrast to the case of 3D
Ising spin glass. The dynamic freezing temperature $T_{f}(H,\omega)$ at which
d$M_{FC}(T,H)/$d$H=\chi^{\prime}(T,H=0,\omega)$, is determined as a function of
frequency (0.01 Hz $\leq \omega/2\pi \leq$ 1 kHz) and magnetic field (0 $\leq H
\leq$ 5 kOe). The dynamic scaling analysis of the relaxation time $\tau(T,H)$
defined as $\tau = 1/\omega$ at $T = T_{f}(H,\omega)$ suggests the absence of
SG phase in the presence of $H$ (at least above 100 Oe). Dynamic scaling
analysis of $\chi^{\prime \prime}(T, \omega)$ and $\tau(T,H)$ near $T_{g}$
leads to the critical exponents ($\beta$ = 0.36 $\pm$ 0.03, $\gamma$ = 3.5
$\pm$ 0.4, $\nu$ = 1.4 $\pm$ 0.2, $z$ = 6.6 $\pm$ 1.2, $\psi$ = 0.24 $\pm$
0.02, and $\theta$ = 0.13 $\pm$ 0.02). The aging phenomenon is studied through
the absorption $\chi^{\prime \prime}(\omega, t)$ below $T_{g}$. It obeys a
$(\omega t)^{-b^{\prime \prime}}$ power-law decay with an exponent $b^{\prime
\prime}\approx 0.15 - 0.2$. The rejuvenation effect is also observed under
sufficiently large (temperature and magnetic-field) perturbations.
