Non-mean-field interpretation of the irreversibility line in spin-glasses

Susceptibility data on an amorphous GdAl spin-glass show an irreversibility onset line t=-A H2φ - and a susceptibility crossover line t=+A H2φ++ (t is reduced temperature; H is field). The exponents φ are both close to 3, and the amplitudes A differ only by a factor of 2. In contrast to earlier explanations of the irreversibility in terms of a de Almeida-Thouless mean-field instability, here both crossovers are explained in terms of a non-mean-field scaling theory.