ANOMALOUS FIELD-DEPENDENT PHENOMENA AT THE SPIN-FLOP TRANSITION IN K2FE(CL1-XBRX)5.H2O SOLID-SOLUTIONS

Hysteresis phenomena associated with the magnetic field is found at the first order spin-flop transition in antiferromagnets K2Fe(Cl1-xBrx)5.H2O (x = 0.1, 0.2 and 0.3). From measurements of the ac susceptibility (chi) and from a study of the dependence of chi with the modulation field (h) at the transition the hysteresis field (DELTA-H*) is determined. DELTA-H* decreases with increasing temperature along the first order line. Magnetization measurements also show an anomalous behavior in presence of a magnetic field (H). No hysteresis was observed in undiluted (x = 0) samples.