Effective exponents for de almeida-thouless line

Abstract

The experimental irreversibility line at the magnetic phase diagram H-T of spin glasses is often approximated using a power law H (x( Tc -T)"*. The mean field theory of de Almeida and Thouless predicts 9=3 for temperatures T close to the spin-glass transition temperature Tc. For a range of reduced temperature involved in an experiment one should use, however, effective exponents (9>3) obtained by fitting the power law to the exact expression for de Almeida-Thouless line. These compare favorably with experimental values of 9 obtained for different spin glasses. The increase of effective exponent up to 9=7 on approaching the spin-glass-ferromagnetism multicritical point is also considered.