Memory and Chaos Effects in Spin Glasses
  New low frequency ac susceptibility measurements on two different spin glasses show that cooling/heating the sample at a constant rate yields an essentially reversible (but rate dependent) X(T) curve; a downward relaxation of X occurs during a temporary stop at constant temperature (ageing). Two main features of our results are: (i)when cooling is resumed after such a stop, X goes back to the reversible curve (chaos) (ii) upon re-heating, X perfectly traces the previous ageing history (memory). We discuss implications of our results for a real space (as opposed to phase space) picture of spin glasses. 
K. Jonason, E. Vincent, J. Hammann, J.P. Bouchaud, P. Nordblad (SPEC,   CEA Saclay, France, and Department of Material Scien...