RANDOM-FIELD EFFECTS AT THE SPIN-FLOP TRANSITION OF DILUTED AND MIXED(K1-XRBX)2FE1-YINY(CL1-ZBRZ)5.H2O

The magnetization of the diluted and mixed low anisotropy antiferromag nets (K1-xRbx)2Fe1-yIny(Cl1-zBrz)5H2O was measured as a function of an applied magnetic field 0 < H < 4.0 T in the temperature range 1.5 < T < 15 K. The focus of this work is on the effects that random fields, generated by an external field applied along the easy axis, have on th e spin-flop transition. The sharp first order transition that occurs i n K2FeCl5H2O has its width increased by almost an order of magnitude w hen substitution is introduced in any of the K, Fe, or Cl sites. In K2 Fe1-yInyCl5H2O and K2Fe(Cl1-zBrz)5H2O hysteseris is also observed. Hys teresis is not observed in (K1-xRbx)2FeCl5H2O.