Experimental study of the spin freezing in an insulating spin-glass: Static and dynamical aspects

We present here a detailed study of the ac susceptibility and nonlinear dc magnetization in the vicinity of $T_f$ in an insulating spin-glass with short-range magnetic interactions, manganese amorphous aluminosilicate. The variation of the freezing temperature $T_f$ with the measuring frequency $\nu$ between 13.5 Hz and 4 MHz can be interpreted by a Fulcher law, but in a wide range of the characteristic parameters ${\tau }_0$ and $T_0$. The behavior of the in-phase and out-of-phase components ${\chi }^{\prime }$ and ${\chi }^{\prime \prime }$ of the ac susceptibility is consistent with a large distribution of relaxation times. The dc magnetizations were studied by means of a superconducting quantum interference device and a fluxmeter in applied fields ranging from 0.01 to 1000 Oe. The rapid increase of the nonlinear susceptibility when approaching $T_f$ is in agreement with the mean-field theory of spin-glasses. We then show that the experimental results can be described by the scaling relation ${\chi }_S(H,\epsilon )=H^{\frac{2}{\delta }}F\left(\frac{\epsilon }{H^{\frac{2}{\phi }}}\right)$ and determine the scaling exponents $\delta =5\mathrm{}\pm 1$ and $\phi =1.1\mathrm{}\pm 0.2$.