Low-field remanent magnetization in Rb 2 FeCl 5 ⋅ H 2 O and in its site-diluted solid solutions Rb 2 Fe 1 − x In x Cl 5 ⋅ H 2 O ( x = 0.04 , 0.08, 0.15, and 0.35)

The observation of remanent magnetization ${M}_{r}$ in single crystals of the easy-axis low-anisotropy antiferromagnet Rb${}_{2}$FeCl${}_{5}\ensuremath{\cdot}$H${}_{2}$O and in its site-diluted solid solutions Rb${}_{2}$Fe${}_{1\ensuremath{-}x}$In${}_{x}$Cl${}_{5}\ensuremath{\cdot}$H${}_{2}$O $(x=0.04$, 0.08, 0.15, and 0.35) is reported. The anomaly is observed when the easy axis of the antiferromagnetic alignment in the crystal is oriented parallel to the applied magnetic field. The values of ${M}_{r}$ depend on the field in which the sample has been cooled and saturates at values as low as 1 Oe. The observed behavior is compared with anomalies previously reported for Mn${}_{1\ensuremath{-}x}$Zn${}_{x}$F${}_{2}$ and K${}_{2}$Fe${}_{1\ensuremath{-}x}$In${}_{x}$Cl${}_{5}\ensuremath{\cdot}$H${}_{2}$O. The saturation values of ${M}_{r}$ for the Rb${}_{2}$Fe${}_{1\ensuremath{-}x}$In${}_{x}$Cl${}_{5}\ensuremath{\cdot}$H${}_{2}$O solid solutions are found to be up to two and five orders of magnitude higher than for, respectively, the K${}_{2}$Fe${}_{1\ensuremath{-}x}$In${}_{x}$Cl${}_{5}\ensuremath{\cdot}$H${}_{2}$O and Mn${}_{1\ensuremath{-}x}$Zn${}_{x}$F${}_{2}$ 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. The scaling of some samples of the Rb-based system, however, deviates from the universal curve. These samples exhibit ${M}_{r}$ values that are higher by one order of magnitude than those that follow the scaling and yet possess the same concentration of nonmagnetic ions. An explanation based on the pinning of antiferromagnetic domain walls by nonmagnetic impurities and lattice defects is given.