LOW-FIELD REMANENT MAGNETIZATION IN RB2FECL5.H2O AND IN ITS SITE-DILUTED SOLID-SOLUTIONS RB2FE1-XINXCL5.H2O (X=0.04, 0.08, 0.15, AND 0.35)

The observation of remanent magnetization M-r in single crystals of th e easy-axis low-anisotropy antiferromagnet Rb2FeCl5 . H2O and in its s ite-diluted solid solutions Rb2Fe1-xInxCl5 . H2O (x=0.04, 0.08, 0.15, and 0.35) is reported. The anomaly is observed when the easy axis of t he antiferromagnetic alignment in the crystal is oriented parallel to the applied magnetic field. The values of M, depend on the field in wh ich the sample has been cooled and saturates at values as low as 1 Oe. The observed behavior is compared with anomalies previously reported for Mn1-xZnxF2 and K2Fe1-xInxCl5 . H2O. The saturation values of M-r f or the Rb2Fe1-xInxCl5 . H2O solid solutions are found to be up to two and five orders of magnitude higher than for, respectively, the K2Fe1- xInxCl5 . H2O and Mn1-xZnxF2 ones. For most of the Rb-based samples as well as for all of the other ones the values of M-r can be scaled to collapse into a single universal curve. Such a curve is independent of the applied magnetic filed, of the value of x, and of the compound. T he scaling of some samples of the Rb-based system, however, deviates f rom the universal curve. These samples exhibit M, values that are high er by one order of magnitude than those that follow the scaling and ye t possess the same concentration of nonmagnetic ions. An explanation b ased on the pinning of antiferromagnetic domain walls by nonmagnetic i mpurities and lattice defects is given.