Almeida-Thouless Line in BiFeO3: Is Bismuth Ferrite a mean field spin   glass?
  Low-temperature magnetic properties of epitaxial BiFeO3 thin films grown on (111)-SrTiO3 substrates have been studied. ZFC and FC magnetization curves show a large discrepency beginning at a characteristic temperature Tf that is dependent on the magnetic-field strengh. Tf(H) varies according to the well known de Aleimda-Thouless line (varies in Hexp(2/3)) suggesting an acentric long rnage spin-glass behavior and mean field system. 
Manoj K. Singh, Ram S. Katiyar, W. Prellier and J.F. Scott