ABSENCE OF HYSTERESIS IN THE HEAT-CAPACITY OF THE 3-DIMENSIONAL RANDOM-FIELD ISING-MODEL

Heat capacity measurements on the prototypical three-dimensional rando m-field Ising model compound Fe0.58Zn0.42F2 have been performed using both the field cooling (FC) and zero-field cooling (ZFC) procedures. T here is no evidence of hysteresis between the FC and ZFC protocols wit hin the experimental accuracy. The absence of hysteresis is interprete d based on a magnetic field-temperature (H-T) phase dia,sram in which a metastability region exists between the Neel temperature line T-N(H) and H-c((1))(T), the latter being the lowest critical field line for the local spin flips.